Effects of a quercetin-rich onion skin extract on 24h ...We investigated the effects of quercetin after regular intake on blood pressure (BP) in overweight-to-obese patients with pre-hypertension

Effects of a quercetin-rich onion skin extract on 24 h ambulatory bloodpressure and endothelial function in overweight-to-obese patients with (pre-)hypertension a randomised double-blinded placebo-controlled cross-over trial

Verena Bruumlll1 Constanze Burak1 Birgit Stoffel-Wagner2 Siegfried Wolffram3 Georg Nickenig4Cornelius Muumlller4 Peter Langguth5 Birgit Alteheld1 Rolf Fimmers6 Stefanie Naaf7 Benno F Zimmermann78Peter Stehle1 and Sarah Egert11Department of Nutrition and Food Sciences Nutritional Physiology University of Bonn 53115 Bonn Germany2Institute of Clinical Chemistry and Clinical Pharmacology University Hospital Bonn 53127 Bonn Germany3Institute of Animal Nutrition and Physiology Christian-Albrechts-University Kiel 24118 Kiel Germany4Department of Cardiology Angiology and Pneumology University Hospital Bonn 53127 Bonn Germany5Department of Biopharmaceutics and Pharmaceutical Technology Institute of Pharmacy and Biochemistry JohannesGutenberg University Mainz 55099 Mainz Germany6Institute of Medical Biometry Informatics and Epidemiology University Hospital Bonn 53127 Bonn Germany7Institut Prof Dr Georg Kurz GmbH 50933 Koumlln Germany8Department of Nutrition and Food Sciences Food Technology and Biotechnology University of Bonn 53117 Bonn Germany

(Submitted 11 March 2015 ndash Final revision received 25 June 2015 ndash Accepted 7 July 2015 ndash First published online 2 September 2015)

AbstractThe polyphenol quercetin may prevent CVD due to its antihypertensive and vasorelaxant properties We investigated the effects of quercetinafter regular intake on blood pressure (BP) in overweight-to-obese patients with pre-hypertension and stage I hypertension In addition thepotential mechanisms responsible for the hypothesised effect of quercetin on BP were explored Subjects (n 70) were randomised to receive162mgd quercetin from onion skin extract powder or placebo in a double-blinded placebo-controlled cross-over trial with 6-week treatmentperiods separated by a 6-week washout period Before and after the intervention ambulatory blood pressure (ABP) and office BP weremeasured urine and blood samples were collected and endothelial function was measured by EndoPAT technology In the total groupquercetin did not significantly affect 24 h ABP parameters and office BP In the subgroup of hypertensives quercetin decreased 24 h systolicBP by minus3middot6mmHg (P= 0middot022) when compared with placebo (mean treatment difference minus3middot9 mmHg P= 0middot049) In addition quercetinsignificantly decreased day-time and night-time systolic BP in hypertensives but without a significant effect in inter-group comparison In thetotal group and also in the subgroup of hypertensives vasoactive biomarkers including endothelin-1 soluble endothelial-derived adhesionmolecules asymmetric dimethylarginine angiotensin-converting enzyme activity endothelial function parameters of oxidation inflammationlipid and glucose metabolism were not affected by quercetin In conclusion supplementation with 162mgd quercetin from onion skin extractlowers ABP in patients with hypertension suggesting a cardioprotective effect of quercetin The mechanisms responsible for the BP-loweringeffect remain unclear

Key words Quercetin Blood pressure Endothelial function Hypertension Cardiovascular diseases

Quercetin (33prime4prime57-pentahydroxyflavone) is one of the pre-dominant flavonoids ubiquitously distributed in (edible) plantsand one of the most potent antioxidants of plant origin(1) Richsources of dietary quercetin are onions kale unpeeled applesberries citrus fruits and tea (Camellia sinensis) In Westernpopulations crude estimates of mean dietary intake appear to

be 10ndash30 mgd(23) As demonstrated in cohort studies dietaryintake of flavonoids in general and of quercetin in particular isassociated with a decreased risk for CVD(24) Although thephysiological mechanisms accounting for this benefit remainincompletely defined animal studies and human interventionstudies have identified many relevant effects ndash for example

Corresponding author S Egert fax +49 228 733217 email segertuni-bonnde

Abbreviations ABP ambulatory blood pressure ACE angiotensin-converting enzyme ADMA asymmetric dimethylarginine BP blood pressure DBP diastolicblood pressure IsoP isoprostanes MAP mean arterial pressure oxLDL oxidised LDL PAT peripheral arterial tonometry RHI reactive hyperaemia indexSBP systolic blood pressure sICAM-1 soluble intercellular adhesion molecule 1 sVCAM-1 soluble vascular cell adhesion molecule 1

British Journal of Nutrition (2015) 114 1263ndash1277 doi101017S0007114515002950copy The Authors 2015 This is an Open Access article distributed under the terms of the CreativeCommons Attribution licence (httpcreativecommonsorglicensesby30) which permits unrestrictedre-use distribution and reproduction in any medium provided the original work is properly cited

supplementation of quercetin may reduce platelet aggrega-tion(56) and plasma concentrations of atherogenic oxidised LDL(oxLDL)(7) In vitro studies suggest that high concentrations ofquercetin (gt1 microM) have anti-inflammatory effects(89) Studies inanimal models (eg obese Zucker rats) suggest beneficialeffects of quercetin on obesity-associated metabolic disordersincluding insulin resistance and dyslipidaemia(10ndash12) Werecently showed that in patients with high CVD risk phenotypechronic supplementation with a supra-nutritional dose of150mgd quercetin significantly reduced systolic blood pres-sure (SBP)(7) Similar findings have been reported by Edwardset al(13) in hypertensive patients and recently by Zahediet al(14) in women with type 2 diabetes mellitus although withpharmacological quercetin doses (500 and 730 mgd) Althoughseveral pathways have been suggested the mechanisms bywhich quercetin possibly affects blood pressure (BP) are notwell-understood These pathways include (i) improvement ofvascular function in an endothelium-dependent orendothelium-independent manner (ii) decrease in oxidativestress andor (iii) interference with the reninndashangiotensinndashaldosterone system(15)One limitation in the interpretation of the BP-lowering effect

of chronic quercetin supplementation is that all human studiespublished to date including our own trial(7) only measured theoffice (clinic) BP in the resting state (typically in the morningwhile fasting) and did not integrate an ambulatory bloodpressure (ABP) monitoring ABP monitoring is considered thegold standard for BP measurement compared with clinic BPmeasurements as it is superior in terms of reliability andvalidity(1617) The superior predictive power of ABP monitoringis probably not only due to its higher number of readingswhich increases the reliability of the measurement but alsodue to its ability to capture the impact of stressors and otherenvironmental factors that occur in daily life and are likely toaffect BP(16) To the best of our knowledge no previous studyhas examined the effects of quercetin on 24 h ABP profiles thusfar Therefore the aim of the present double-blinded placebo-controlled cross-over trial was to systematically investigate theeffects of quercetin on arterial BP (office BP and 24 h ABPprofiles) in adults with pre-hypertension and stage I hyperten-sion and to explore mechanisms involved in the BP-loweringefficacy of quercetin Furthermore effects of quercetin on lipidand glucose metabolism were investigated

Methods

Subjects

Overweight-to-obese subjects were recruited from the com-munity of the city of Bonn Germany via public postings flyersand advertisements in the local newspaper From a total of 500interested subjects 154 individuals aged 25ndash65 years with a BMIof 25ndash35 kgm2 attended a screening which included physicalassessments (body height and weight resting BP heart ratewaist and hip circumference) clinical assessments (liver func-tion serum lipids and lipoproteins glucose and uric acidhaematology high-sensitive C-reactive protein (hs-CRP))medical history and a dietary questionnaire

Participants were included if they had the following traits ofthe metabolic syndrome (i) central obesity (waist circumferencege94 cm for men and ge80 cm for women) (ii) pre-hypertension(ge120ndash139mmHg SBP andor ge80ndash89mmHg diastolic bloodpressure (DBP)) or stage I hypertension (ge140ndash159mmHgSBP andor ge90ndash99mmHg DBP) (iii) dyslipidaemia (fastingserum TAG concentrations ge1middot7mmoll andor serumconcentrations of HDL-cholesterol lt1middot0mmoll for men andlt1middot3mmoll for women) andor a proinflammatory state(hs-CRPge 2mgl)(1819) Main exclusion criteria were as followssmoking diagnosed type 2 diabetes mellitus liver gastro-intestinal or diagnosed inflammatory diseases a history ofcardiovascular events untreated thyroid dysfunction cancerrecent major surgery or illness pregnancy or breast feedingalcohol abuse consumption of polyphenol-rich supplementsparticipation in a weight loss programme and Raynaudrsquossyndrome

A total of seventy subjects (thirty-five male thirty-five female)were included into the study During the first interventionperiod two subjects dropped out for personal reasons Onlydata from the remaining sixty-eight subjects (thirty-four malethirty-four female) who completed the entire interventionstudy were included in the analysis and are subsequentlyreported The participant flow from the initial screening to finalanalysis is shown in Fig 1

The study protocol was explained in detail to all the participantswho gave their written informed consent at the beginning of thestudy The study protocol was approved by the ethics committee ofthe Medical Faculty of the Rheinische Friedrich-Wilhelms-Universitaumlt Bonn Germany and was in accordance with theHelsinki declaration The trial was registered at wwwgermanctrde and httpappswhointtrialsearch as DRKS00000555

The subjects were instructed to maintain their habitualdiet physical activity levels lifestyle factors and body weightParticipants taking oral contraceptives (n 4 women) orantihypertensive (n 12) or thyroid drugs (n 9) were instructed tocontinue taking their medication without changes

Study design

This study was a double-blinded randomised placebo-controlled cross-over trial with 6-week treatment periodsseparated by a 6-week washout period Subjects were instruc-ted to take a total of three capsules per d one capsule with eachprincipal meal Two kinds of hard gelatin capsules ndash quercetinand placebo ndash were manufactured at the Institute of Pharmacyand Biochemistry Johannes Gutenberg University MainzQuercetin capsules were filled with onion skin extract powder(132 mgcapsule) placebo capsules contained mannitol(approximately 170mgcapsule) For the production of theonion skin extract powder onion skins were washed with waterand then extracted using ethanol Thereafter the extractionsolvent was removed by evaporation The resulting suspensionwas decanted and subsequently vacuum-dried The flavonoidcontents of the onion skin extract and of quercetin capsuleswere determined by HPLC with diode-array detection Theidentity of the flavonoids was confirmed by MSMS The resultsof quantification are shown in Table 1 The quercetin content of

1264 V Bruumlll et al

the onion skin extract powder (Allium cepa L Rudolf WildGmbH amp Company KG) was 41middot25 (dry mass 95middot94 ) Eachquercetin capsule contained 54 mg quercetin Hard gelatincapsules (Coni-Snapreg) size 0 were supplied by CapsugelQuercetin and placebo capsules were identical in shape andtaste Capsule filling was carried out using a Dott Bonapacesemi-automatic capsule filling machine Mannitol was obtainedfrom Fagron Quality was checked by determining the homo-geneity of weight distributions of a sample of twenty rando-mised capsules taken from each batch Furthermore themicrobiological burden of the capsules was determined fol-lowing manufacture and before release Primary packaging wasinto blister packages The primary investigators all study per-sonnel and all the participants were blinded to the treatmentsA quercetin dosage of 162mg per d (three capsules) wasselected to represent the 10- to 15-fold of the estimated mean

daily quercetin intake in Germany(20) and other Europeanpopulations(21) Plasma kinetics of this quercetin dosage afterbolus intake was examined previously(2223)

Subjects were assigned to quercetin or placebo treatmentaccording to a block-wise randomisation scheme Separatecomputer-generated randomisation schedules for men andwomen were created to stratify subjects by sex with an attemptto achieve a distribution between men and women of 5050 ineach treatment group Randomisation allocation to either oneof the capsules and capsule handling were carried out by anindependent researcher (B A) Capsules were handed out ondays 0 and 21 of each treatment period with a surplus of 20 Leftovers and empty blisters were collected on days 21 and 42Compliance was monitored by determining quercetin plasmaconcentrations after the treatment periods (see below) bycounting capsules at the end of the study and by instructing

Assessed for eligibility bytelephone (n 500)

Complete screening withphysical and clinical

assessment medical historyand dietary questionnaire

(n 154)

Excluded (n 346) diams Not meeting inclusion criteria (n 206) diams Declined to participate (n 31) diams Other reasons (n 109)

Randomly assigned tocrossover trial (n 70)

Excluded (n 84) diams Not meeting inclusion criteria (n 74) diams Withdrew (n 6) diams Other reasons (n 4)

Allocated to receive quercetin(n 35)

Allocated to receive placebo(n 35)

Washout (n 34) Washout (n 34)

Drop out (n 1) Drop out (n 1)

Analysed for outcomes in the total study group (n 68)

diams Office BP and heart rate

diams 24 h ABP monitoring

diams Anthropometric data

diams Bloodurine analyses

diams Dietary intake of energy nutrients and quercetin

Analysed for outcomes in subgroups

diamsOffice BP heart rate and 24 h ABP monitoring in hypertensive patients selected according to BP classification (17 24)

diams Vascular testing (n 48)

Enrolment

Crossover

Allocation

Analyses

- office BP and heart rate (n 59 and n 55 for quercetin and placebo) - 24 h ABP monitoring (n 31 and n 29 for quercetin and placebo)

Fig 1 Flow diagram of participants ABP ambulatory blood pressure BP blood pressure

Effects of quercetin on blood pressure 1265

subjects to document capsule consumption potentialobserved side-effects deviations from their normal physicalactivity and any other observations considered relevant in astudy diarySubjects were instructed to keep 3-d food records at the

beginning and at the end of each treatment period Each recordrepresented the food and beverage intake of 2 weekdays and1 weekend day These dietary records were used to calculatethe habitual dietary intake of energy nutrients and quercetinSample size was calculated based on office BP data from our

previous trial(724) and expected changes in SBP The calculationrevealed that forty-nine subjects had to complete the study toreach a 90 power with a significance level of 0middot01 to detect a3 mmHg difference in BP between the quercetin and placebogroups (SD of the within-subject was different from the SBP3middot8 mmHg) With the assumption of a 30 dropout rate weaimed to randomly assign approximately seventy participantsThe measurements of 24 h ABP office BP heart rate vascular

testing and anthropometric measurements were conducted atthe beginning and at the end of the two intervention periods

Measurements

Office blood pressure and heart rate Measurements ofoffice BP and heart rate were obtained using an automatic BPmeasurement device (boso carat professional Bosch+Sohn) understandardised conditions according to the recommendations of theAmerican Heart Association Council on High Blood PressureResearch(25) Each participant sat quietly for 5ndash10min after whichtheir arm was placed at heart level and SBP and DBP weremeasured at least twice in 3- to 5-min intervals If BP measurementsvaried by 10mmHg an additional measurement was performedThe accumulated measurements were then averaged to determineoverall SBP and DBP The mean arterial pressure (MAP) wascalculated as follows (DBP+13 (SBPminusDBP))

24 h ambulatory blood pressure monitoring The 24 h ABPand heart rate recordings were taken every 15min between0600 and 2200 hours (day-time) and every 30 min between2200 and 0600 hours (night-time) using an ABP monitor(Spacelabs monitor type 90207) on the non-dominant arm Onthe day of measurement subjects were instructed to maintain

their habitual activity level and to refrain from strenuousexercise We assessed the following BP parameters 24 hday-time and night-time SBP DBP MAP heart rate and thenocturnal dip in SBP and DBP

Vascular testing For vascular testing we used the noninvasiveperipheral arterial tonometry (PAT) technology to assess thereactive hyperaemia index (RHI) and the augmentation index (AI)using the EndoPAT plethysmographic device (Endo-PAT2000)Details have been described elsewhere(26) In brief the PAT signalindicates changes of the peripheral arterial tone in peripheralarterial beds by recording the arterial pulsatile volume changesfrom the fingertip For that purpose we placed a pair ofplethysmographic biosensors on both index fingers and a BP cuffon the upper arm of the study arm (left arm) whereas the rightarm served as the control arm (without a cuff) The recording ofthe PAT signal started after a resting period of at least 15min witha 1min standby-test period If the signal recording was free frominterferences the test period started with a 5min baselinerecording of the pulse wave amplitude Subsequently the BP cuffwas inflated for 5min to supra-systolic values to induce ischaemiawhereupon the cuff was deflated This resulted in reactivehyperaemia while further recording for 5min PAT signals wereanalysed with automated software (Itamar Medical) and RHI wascalculated as the ratio of the average PAT signal amplitude over a1min period starting 1min after cuff-deflation divided by theaverage PAT signal amplitude over a 3middot5min period at thebaseline recording followed by normalisation of the values fromthe study arm to the control arm The RHI correlates with brachialartery flow-mediated dilatation(27) and is significantly influencedby nitric oxide (NO)(28) A lower RHI was found in subjects withcoronary endothelial dysfunction(29) and in the presence of CVDrisk factors(30)

Anthropometrics Body height was determined on a stadiometerto the nearest 0middot1 cm Body weight was determined to the nearest100 g Waist circumference was measured midway between thelowest rib and the ilial crest while the subject was at minimalrespiration Hip circumference was measured at the height oftrochanteres majores Body composition was measured by bioe-lectrical impedance analysis (Nutrigard-M Multi Frequency Phase-Sensitive Bioelectrical Impedance Analyzer Data Input) Fat-freemass (FFM) was calculated in accordance with Sun et al(31)fat mass was calculated by subtracting FFM from body weight

Bloodurine sample processing and analysis

Fasting venous blood samples were collected on the first andthe last visit of each intervention period between 0630 and0900 hours under standardised conditions The subjects wereinstructed to abstain for 24 h from alcoholic beverages and weretold not to engage in strenuous exercise on the day beforeblood sampling The last capsule was taken in the eveningbefore blood sampling Blood was drawn into tubes containingEDTA lithium heparin fluoride or a coagulation activator(Sarstedt) Plasmaserum was obtained by centrifugation at3000 g for 15 min at 8degC Plasmaserum aliquots were

Table 1 Flavonoid analysis in onion skin extract powder(Mean values and standard deviations)

(g100 g)

Compound Mean SD

Quercetin 44middot2 0middot15Quercetin dihexoside 0middot04523 0middot00027Quercetin hexoside 1 0middot1557 0middot0072Quercetin hexoside 2 1middot79 0middot017Methylquercetin hexoside 0middot0481 0middot00030Kaempferol 0middot122 0middot0017Methylquercetin 0middot0740 0middot00033

Analyses were conducted in duplicate

immediately frozen in cryovials and stored at minus80degC until ana-lysis All the laboratory measurements were performed withoutknowledge of the treatment All serum and plasma samples ofone subject were analysed in the same assay runSerum concentration of total cholesterol was measured using

polychromatic endpoint-measurement whereas serum con-centrations of LDL-cholesterol HDL-cholesterol TAG and plasmaconcentrations of glucose were measured using bichromaticendpoint-measurement with a Dimension Vista 1500 analyser(Siemens Healthcare Diagnostics) Serum concentrations of apoB A1 and hs-CRP were determined using nephelometric methodswith a Dimension Vista 1500 analyserSerum insulin concentration was measured using a chemilumi-

nescentndashimmunometric assay with the Immulite 2000 analyser(Siemens Healthcare Diagnostics) Insulin resistance was measuredusing the homoeostatic model assessment (HOMA) and calculatedas the product of the fasting plasma insulin concentration (in μUml)and the fasting plasma glucose concentration (in mmoll) dividedby 22middot5(32) HbA1c was measured using an HPLC-method witha Variant II analyser (Bio-Rad Laboratories) Serum concentrationsof angiotensin-converting enzyme (ACE) were measured using aphotometric method (Buehlmann Laboratories) with a DimensionVista 1500 analyserPlasma ADMA (Immundiagnostik) plasma oxLDL (Immundiag-

nostik) serum endothelin-1 and serum-soluble adhesion moleculesE-selectin soluble intercellular adhesion molecule 1 (sICAM-1)and soluble vascular cell adhesion molecule 1 (sVCAM-1) (RampDsystems) were determined in duplicate using commerciallyavailable enzyme-linked immunoassay kits according to themanufacturerrsquos instructions and quality controls Plasmaconcentration of L-arginine was determined using reversed-phaseHPLC as described previously(33)Analyses of plasma concentrations of quercetin its

monomethylated derivatives tamarixetin (4prime-O-methyl quercetin)and isorhamnetin (3prime-O-methyl quercetin) as well as of thedehydroxylated quercetin metabolite kaempferol were carriedout using HPLC with fluorescence detection as describedpreviously(34) All the samples were treated enzymatically withβ-glucuronidasesulphatase before the extraction of the flavonolsTotal plasma flavonols were calculated as follows total flavonols(nmoll)=quercetin (nmoll) +kaempferol (nmoll) + isorhamnetin(nmoll) + tamarixetin (nmoll)First morning urine samples were collected on the first and

the last visit of the intervention periods 0middot002 of butylatedhydroxytoluene was added and the urine was frozen at minus80 degCuntil analysis From these urine samples 8-iso-PG F2α (8-iso-PGF2α) and 23-dinor-15-F2t-IsoP were measured by UHPLC-MSMS Urinary creatinine levels were determined using abichromatic kinetic method (Jaffeacute method)

Self-reported dietary intake of energy nutrients andquercetin

The self-reported intakes of energy macronutrients dietaryfibre and antioxidant pro-vitaminsvitamins were calculatedusing the computer-based nutrient calculation programmeEBISpro (University of Hohenheim) based on the German

Nutrient Database Bundeslebensmittelschluumlssel (Max Rubner-Institute) The quercetin intake was estimated using the USDAflavonoid database(35)

Statistical analyses

All the statistical analyses were performed using IBM SPSSstatistical software package (version 20) Differences betweensexes at screening were tested using the unpaired Studentrsquost test or the MannndashWhitney U test Baseline values werecompared between groups using paired Studentrsquos t tests orWilcoxon signed-rank tests Intra-group (baseline v endpoint)and inter-group comparisons (changes during quercetin vchanges during placebo treatment) of normally distributed datawere performed using paired Studentrsquos t tests Intra-group andinter-group comparisons of data that were not normally dis-tributed which was mainly the case for serum TAG plasmaglucose serum insulin HOMA IR index plasma oxLDL serumhs-CRP and urinary IsoP were conducted by Wilcoxon signed-rank tests (for details see footnotes in Tables)

Interaction effects between the stage of hypertension andtreatment assignment were tested using a univariate ANOVAwith the respective variables as fixed factors In all cases avalue for Ple 0middot05 (two-sided) was taken to indicate significanteffects Pearsonrsquos correlation coefficient was used to assessrelationships between BP variables (SBP and DBP) and bio-markers of inflammationendothelial function and also betweenBP variables and plasma flavonols A test for carry-over effectsaccording to Kenward and Jones(36) was used No carry-overeffects between the two treatment periods could be observedAll the analyses are presented on a per-protocol basis For allsixty-eight participants complete data sets were available

All data were analysed for the whole study group (n 68) andalso for the subgroup of patients with hypertension Office BPdata were classified according to Chobanian et al(18) Classifi-cation of ABP data was conducted as described by Pickeringet al(25) (for details see footnotes in Table 4)

Results

Subject characteristics at screening compliance and dietaryintake

Characteristics of the participants at screening are presented inTable 2 As planned all subjects were overweight (43 ) orobese (57 ) had a visceral fat distribution and were pre-hypertensive or stage 1 hypertensive We observed sex differ-ences with respect to body height body weight waist and hipcircumference waisthip ratio and fasting serum concentrationsof TAG total cholesterol HDL-cholesterol and plasma glucose(Table 2)

Count of returned capsules indicated an almost full com-pliance of 98middot2 (SD 2middot6) and 98middot0 (SD 4middot1) during quercetinand placebo consumption respectively Compliance to quer-cetin supplementation was objectively confirmed by a markedincrease in plasma concentrations of quercetin and total flavo-nols by 1149middot6 (Plt 0middot0001) and 828middot6 (Plt 0middot0001)respectively (Fig 2(a) and (b)) The increase was measurable in

all patients receiving quercetin In addition plasma concentra-tions of kaempferol isorhamnetin and tamarixetin significantlyincreased after quercetin but not after placebo supplementation(data not shown) There was a high inter-individual variation inplasma quercetin concentrations already at baseline (range forall study subjects 0middot2ndash330middot5 nmoll) and after quercetin sup-plementation (99middot1ndash1313middot1 nmoll)Analyses of 3-d dietary records indicated no significant inter-

group and intra-group differences in mean daily intakes ofenergy protein carbohydrates total fat fatty acids cholesterolantioxidants (eg vitamin E vitamin C) dietary fibre andquercetin (data not presented in Tables) Dietary quercetinintake was 11middot3 (SD 11middot9) mgd and 9middot0 (SD 8middot1) mgd at thebeginning and at the end of the quercetin treatment respec-tively and 11middot7 (SD 11middot2) mgd and 9middot2 (SD 8middot2) mgd at thebeginning and at the end of the placebo treatment respectivelyMain dietary quercetin sources were onions apples and tea

Body weight waist and hip circumference bodycomposition and potential side-effects

Quercetin supplementation did not significantly affect bodyweight waist and hip circumference relative fat mass or fat-freemass (data not shown) Participants did not report any side-effects neither during quercetin nor during placebo treatment

Ambulatory blood pressure monitoring and office bloodpressure

In the entire study group (n 68) quercetin and placebo sup-plements did not significantly affect mean 24 h day-time andnight-time ABP parameters (SBP DBP MAP nocturnal dip inSBP and DBP) In addition office BP (SBP and DBP MAP) was

not significantly changed by quercetin or placebo treatment asanalysed for the entire study group (Table 3) Resting SBP atbaseline and the change in SBP from baseline to after inter-vention were significantly correlated with those individualswith higher baseline SBP demonstrating greater reductions inSBP in response to the quercetin treatment (r minus 0middot508Plt 0middot0001 n 68) We also found a significant interaction effectbetween stage of hypertension and treatment assignment forthe decreases in mean 24 h SBP (P= 0middot008) and in day-time SBP(P= 0middot024) but not for the decrease in night-time SBP(P= 0middot568) (data not shown) There were also significantinteraction effects between stage of hypertension and treatmentassignment for decreases in mean 24 h MAP (P= 0middot014) and inday-time MAP (P= 0middot032) but not for decreases in night-timeMAP (P= 0middot176) (data not shown)

Effects of supplementation with quercetin or placebo on ABPprofiles and office BP in the subgroup of hypertensive patientsare presented in Table 4 Note that there are different n valuesfor quercetin and placebo treatment because the initial BP ofthe participants at the beginning of the quercetin and placeboperiod slightly differed In some cases this physiological dif-ference led to a different BP classification When comparedwith placebo (treatment difference minus3middot9 (SD 11middot1) mmHgP= 0middot049 Table 4) quercetin significantly decreased mean 24 hSBP by minus3middot6 (SD 8middot2) mmHg (P= 0middot022) from baseline in thesubgroup of stage 1 hypertensive subjects (n 31) Changes inday-time SBP and night-time SBP during quercetin treatmentwere not significantly different from placebo treatmentHowever quercetin significantly decreased day-time SBPby minus4middot6 (SD 9middot0) mmHg (P= 0middot014) and night-time SBP by minus6middot6(SD 9middot9) mmHg (P= 0middot007) (Table 4) In addition changes in24 h MAP day-time MAP and night-time MAP during quercetindid not differ significantly from placebo However quercetinsignificantly reduced mean 24 h MAP day-time MAP and night-

Table 2 Subject characteristics and blood parameters at screening(Mean values and standard deviations)

Total (n 68) Women (n 34) Men (n 34)

Mean SD Mean SD Mean SD Women v men (P)

Age (years) 47middot4 10middot5 48middot2 10middot4 46middot6 10middot6 0middot396Body height (cm) 173middot8 9middot6 168middot2 9middot0 179middot3 6middot6 lt0middot0001Body weight (kg) 94middot4 16middot1 88middot8 15middot5 99middot9 14middot9 0middot021BMI (kgm2) 31middot1 3middot4 31middot3 3middot6 31middot0 3middot2 0middot677Overweight () 43 50 35Obese () 57 50 65Waist circumference (cm) 103middot9 10middot4 99middot0 8middot5 108middot7 10middot0 0middot008Hip circumference (cm) 111middot5 8middot7 115middot3 8middot8 107middot7 6middot7 0middot001Waisthip ratio 0middot93 0middot09 0middot86 0middot05 1middot01 0middot05 lt0middot0001Systolic BP (mmHg) 144middot4 12middot6 141middot7 13middot4 147middot2 11middot3 0middot077Diastolic BP (mmHg) 94middot2 8middot4 94middot2 8middot1 94middot3 8middot8 0middot687Heart rate (beats per min) 73middot0 9middot6 74middot1 9middot1 71middot8 10middot2 0middot496Serum TAG (mmoll) 1middot98 1middot04 1middot71 0middot82 2middot25 1middot17 0middot014Serum total cholesterol (mmoll) 5middot69 1middot15 5middot97 1middot21 5middot41 1middot03 0middot042Serum HDL-cholesterol (mmoll) 1middot46 0middot34 1middot64 0middot33 1middot27 0middot23 lt0middot0001Serum LDL-cholesterol (mmoll) 3middot59 0middot93 3middot72 0middot95 3middot45 0middot89 0middot232Plasma glucose (mmoll) 5middot19 0middot55 5middot00 0middot42 5middot38 0middot60 0middot013Serum insulin (pmoll) 67middot9 43middot4 57middot9 24middot5 77middot2 54middot4 0middot082Serum hs-CRP (mgl) 3middot19 6middot04 2middot93 3middot22 3middot45 7middot98 0middot690

BP blood pressure hs-CRP high-sensitive C-reactive protein

Table 3 Measurements of the 24 h ambulatory blood pressure and office blood pressure in the total study group during the 6-week dietary supplementation with quercetin or placebo(Mean values and standard deviations)

Quercetin (n 68) Placebo (n 68)

Baseline Endpoint Mean changeP intra-group

Baseline Endpoint Mean changeP intra-group P inter-group

Treatment difference

Mean SD Mean SD Mean SD comparison Mean SD Mean SD Mean SD comparison comparison Mean SD

24 h ABP monitoringSystolic BP (mmHg) 133middot3 10middot2 132middot4 9middot0 minus0middot9 7middot3 0middot329 132middot5 8middot4 132middot4 9middot6 minus0middot1 6middot0 0middot848 0middot460 minus0middot8 9middot1Diastolic BP (mmHg) 82middot0 8middot5 81middot4 7middot6 minus0middot7 5middot3 0middot304 81middot4 7middot1 80middot9 8middot5 minus0middot4 4middot5 0middot425 0middot711 minus0middot2 6middot8MAP (mmHg) 99middot5 8middot7 98middot6 7middot5 minus0middot9 6middot1 0middot227 98middot8 7middot0 98middot4 8middot3 minus0middot4 4middot7 0middot520 0middot977 minus0middot5 7middot7Heart rate (beats per min) 74middot3 8middot2 76middot3 8middot2 +2middot0 5middot3 0middot003 74middot5 9middot8 75middot1 8middot7 +0middot7 5middot9 0middot372 0middot189 +1middot3 8middot1Nocturnal dip in systolic BP () 11middot0 6middot6 11middot3 5middot7 +0middot3 6middot1 0middot726 10middot7 5middot6 12middot0 4middot8 +1middot3 6middot5 0middot105 0middot368 minus1middot1 9middot5Nocturnal dip in diastolic BP () 15middot9 7middot1 16middot9 6middot8 +1middot0 6middot4 0middot217 16middot0 6middot7 17middot5 6middot2 +1middot5 7middot3 0middot101 0middot669 minus0middot6 10middot6Day-time (0600ndash2200 hours)

Systolic BP (mmHg) 136middot6 10middot6 135middot7 9middot4 minus0middot9 7middot6 0middot347 135middot5 8middot5 136middot1 9middot7 +0middot6 6middot2 0middot440 0middot172 minus1middot6 9middot2Diastolic BP (mmHg) 85middot0 8middot7 84middot5 7middot9 minus0middot5 5middot6 0middot457 84middot3 7middot2 84middot2 8middot6 minus0middot0 4middot7 0middot932 0middot538 minus0middot5 6middot9MAP (mmHg) 102middot5 8middot8 101middot8 7middot9 minus0middot8 6middot4 0middot315 101middot4 7middot1 101middot7 8middot4 +0middot3 4middot9 0middot640 0middot257 minus1middot1 7middot8Heart rate (beats per min) 76middot2 8middot7 78middot2 8middot6 +1middot9 5middot6 0middot006 76middot7 10middot5 77middot5 9middot2 +0middot7 6middot4 0middot367 0middot202 +1middot3 8middot4Night-time (2200ndash0600 hours)

Systolic BP (mmHg) 121middot4 11middot7 120middot3 10middot4 minus1middot1 9middot0 0middot322 120middot9 10middot5 119middot6 9middot8 minus1middot3 9middot1 0middot238 0middot921 +0middot2 14middot0Diastolic BP (mmHg) 71middot4 9middot2 70middot1 8middot0 minus1middot3 6middot4 0middot106 70middot8 8middot7 69middot4 8middot5 minus1middot4 6middot4 0middot085 0middot946 +0middot8 9middot9MAP (mmHg) 88middot5 9middot9 87middot0 8middot0 minus1middot5 7middot4 0middot093 88middot1 9middot1 86middot7 8middot5 minus1middot4 7middot5 0middot139 0middot911 minus0middot2 11middot5Heart rate (beats per min) 66middot9 8middot7 69middot2 8middot8 +2middot4 6middot6 0middot004 67middot4 9middot8 68middot1 9middot1 +0middot7 7middot3 0middot459 0middot203 +1middot7 10middot7Office BP

Systolic BP (mmHg) 144middot4 16middot8 146middot9 17middot2 +2middot5 10middot7 0middot063 143middot9 14middot4 143middot8 17middot4 minus0middot1 10middot9 0middot937 0middot171 +2middot6 15middot3Diastolic BP (mmHg) 98middot2 11middot3 97middot2 9middot7 minus1middot0 8middot5 0middot338 97middot3 10middot0 96middot1 11middot0 minus1middot2 7middot3 0middot166 0middot863 +0middot2 11middot5MAP (mmHg) 113middot6 12middot5 113middot8 11middot6 +0middot2 8middot5 0middot879 112middot8 10middot7 112middot0 12middot6 minus0middot9 7middot7 0middot361 0middot472 +1middot0 11middot6Heart rate (beats per min) 64middot6 7middot9 65middot7 8middot3 +1middot1 5middot5 0middot112 63middot9 9middot1 65middot6 8middot0 +1middot6 6middot4 0middot040 0middot598 minus0middot5 8middot2

ABP ambulatory blood pressure BP blood pressure MAP mean arterial pressure The two groups did not differ significantly with regard to any of the variables at baseline (paired Studentrsquos t tests or Wilcoxon signed-rank tests)

Effects

ofquercetin

onbloodpressu

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time MAP from baseline by minus2middot8 (SD 7middot3) mmHg (P= 0middot043) byminus3middot3 (SD 8middot0) mmHg (P= 0middot042) and by minus6middot7 (SD 8middot3) mmHg(P= 0middot001) respectively (Table 4)Treatment with quercetin did not significantly change the

nocturnal dip in SBP and DBP In addition systolic and diastolicoffice BP were not significantly changed by quercetin or pla-cebo treatment in hypertensive patients (Table 4)

Serum lipids lipoproteins apolipoproteins glucose andinsulin

No significant inter-group differences were found for the effectsof quercetin or placebo on serum lipids lipoproteins apoli-poproteins glucose and insulin Furthermore quercetin sup-plementation did not significantly affect fasting serum totalcholesterol LDL-cholesterol HDL-cholesterol TAG apo B andA1 insulin plasma glucose and HbA1c neither in the total study

group nor in the subgroup of hypertensive patients (intra-groupcomparisons Table 5)

Soluble adhesion molecules asymmetric dimethylarginineangiotensin-converting enzyme C-reactive proteinendothelial function and oxidation

For the total study group quercetin supplementation did notsignificantly affect fasting serum concentrations of endothelin-1sE-selectin and sVCAM-1 (Table 6) When compared withplacebo quercetin did not significantly affect serum sICAM-1(treatment difference minus5middot3 (SD 30middot7) ngml P= 0middot219 Table 6)However quercetin decreased fasting serum sICAM-1 frombaseline by minus8middot2 (SD 17middot2) ngml (intra-group comparisonPlt 0middot001) Neither quercetin nor placebo significantly alteredfasting plasma concentrations of the endogenous NO synthaseinhibitor ADMA the corresponding ratio of L-arginine to ADMA

Week 0 Week 6

dagger

Fig 2 Fasting plasma concentrations of quercetin (a) (n 68) and total flavonols (b) (n 68) before and after the 6-week supplementation with quercetin (162mgd) orplacebo () Values are means and standard deviations represented by vertical bars Mean value was significantly different from baseline (Plt 0middot0001 intra-groupcomparison) dagger Change during quercetin treatment was significantly different from change during placebo treatment (Plt 0middot0001 inter-group comparison) Total plasmaflavonols were calculated as follows total flavonols (nmoll)= quercetin (nmoll) + kaempferol (nmoll) + isorhamnetin (nmoll) + tamarixetin (nmoll) The two groups didnot differ significantly with regard to plasma concentrations of quercetin and total flavonol at baseline (Wilcoxon signed-rank tests)

Table 4 Measurements of the 24 h ambulatory blood pressure and office blood pressure in the subgroup of hypertensive patients during the 6-week dietary supplementation with quercetin or placebo(Mean values and standard deviations)

Quercetin Placebo

24 h ABP monitoringdagger (n 31) (n 29)Systolic BP (mmHg) 141middot5 7middot3 137middot9 7middot3 minus3middot6 8middot2 0middot022 139middot7 5middot3 140middot2 6middot4 +0middot5 6middot4 0middot690 0middot049 minus3middot9 11middot1Diastolic BP (mmHg) 88middot7 6middot6 86middot6 5middot9 minus2middot1 6middot2 0middot074 86middot6 6middot1 86middot9 7middot3 +0middot3 3middot9 0middot680 0middot124 minus2middot8 8middot3MAP (mmHg) 106middot4 6middot5 103middot7 5middot9 minus2middot8 7middot3 0middot043 104middot4 5middot4 104middot7 6middot5 +0middot3 4middot4 0middot710 0middot151 minus3middot0 9middot7Heart rate (beats per min) 76middot1 8middot3 77middot9 8middot6 +1middot8 5middot5 0middot081 76middot6 10middot8 77middot5 9middot7 +0middot9 5middot9 0middot445 0middot435 +1middot3 7middot9Nocturnal dip in systolic BP () 12middot1 6middot5 12 6middot6 +0middot3 5middot4 0middot758 9middot6 5middot8 12middot5 5middot9 +2middot9 7middot1 0middot035 0middot142 minus2middot8 8middot7Nocturnal dip in diastolic BP () 16middot1 7middot7 16middot9 7middot6 +0middot8 5middot8 0middot477 13middot9 7middot6 17middot3 7middot8 +3middot3 8middot7 0middot051 0middot213 minus2middot5 9middot5

Day-time (0600ndash2200 hours)Dagger (n 27) (n 23)Systolic BP (mmHg) 146middot4 6middot7 141middot8 7middot7 minus4middot6 9middot0 0middot014 144middot5 4middot4 144middot6 6middot3 +0middot1 5middot9 0middot964 0middot109 minus4middot9 12middot1Diastolic BP (mmHg) 92middot9 5middot8 90middot4 6middot3 minus2middot5 6middot9 0middot070 90middot3 6middot5 90middot9 7middot4 +0middot5 2middot9 0middot399 0middot111 minus3middot6 9middot0MAP (mmHg) 110middot8 5middot9 107middot54 6middot5 minus3middot3 8middot0 0middot042 108middot4 5middot2 108middot8 6middot5 +0middot4 3middot6 0middot644 0middot110 minus4middot2 10middot6Heart rate (beats per min) 79middot2 9middot0 80middot8 9middot1 +1middot6 6middot3 0middot211 79middot0 9middot9 80middot5 9middot3 +1middot4 6middot7 0middot311 0middot793 minus0middot6 9middot1

Night-time (2200ndash0600 hours)sect (n 21) (n 27)Systolic BP (mmHg) 134middot7 8middot4 128middot1 9middot6 minus6middot6 9middot9 0middot007 131middot1 6middot7 126middot1 9middot8 minus5middot0 10middot6 0middot021 0middot667 minus2middot2 18middot8Diastolic BP (mmHg) 80middot6 9middot4 75middot8 8middot1 minus4middot9 7middot2 0middot006 78middot8 6middot5 75middot7 8middot2 minus3middot1 7middot6 0middot045 0middot289 minus3middot5 11middot8MAP (mmHg) 99middot7 8middot5 93middot0 7middot9 minus6middot7 8middot3 0middot001 96middot6 6middot9 92middot9 8middot6 minus3middot8 8middot9 0middot037 0middot345 minus3middot8 14middot4Heart rate (beats per min) 68middot7 8middot5 71middot6 9middot3 +2middot9 6middot3 0middot049 69middot5 11middot0 67middot5 8middot5 minus2middot0 8middot7 0middot235 0middot127 +4middot3 9middot8

Office BP (n 59) (n 55)Systolic BP (mmHg) 147middot1 16middot2 149middot3 17middot0 +2middot2 10middot9 0middot131 147middot8 12middot7 147middot2 16middot9 minus0middot6 11middot6 0middot685 0middot311 +2middot3 16middot3Diastolic BP (mmHg) 100middot3 10middot6 98middot6 9middot6 minus1middot7 8middot7 0middot138 100middot7 8middot0 98middot8 10middot2 minus1middot8 7middot5 0middot072 0middot972 minus0middot1 12middot4MAP (mmHg) 115middot9 11middot7 115middot5 11middot4 minus0middot4 8middot7 0middot718 116middot4 8middot6 114middot9 11middot8 minus1middot4 8middot0 0middot186 0middot676 +0middot7 12middot5Heart rate (beats per min) 65middot0 7middot6 65middot9 8middot0 +0middot8 5middot5 0middot256 64middot4 8middot9 65middot8 7middot9 +1middot3 6middot1 0middot109 0middot575 minus0middot6 8middot2

ABP Ambulatory blood pressure BP blood pressure MAP mean arterial pressure The two groups did not differ significantly with regard to any of the variables at baseline (paired Studentrsquos t tests or Wilcoxon signed-rank tests) All the subjects participated in both treatments There are different n values for quercetin and

placebo treatment because the initial blood pressure of the participants at the beginning of the quercetin and placebo treatment period slightly differed In some cases this physiological difference led to a different blood pressureclassification

dagger Systolic BPgt135 andor diastolic BPgt85mmHg (according to reference 25)Dagger Systolic BPgt140 andor diastolic BPgt90mmHg (according to reference 25)sect Systolic BPgt125 andor diastolic BPgt75mmHg (according to reference 25) Stage 1 hypertensive systolic BPge140 andor diastolic BPge90mmHg (according to reference 18)

Effects

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onbloodpressu

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Table 5 Fasting lipids lipoproteins apolipoproteins insulin glucose HbA1c and HOMA IR Index in the total study group (n 68) during the 6-week dietary supplementation with quercetin or placebo(Mean values and standard deviations)

Baseline EndpointMeanchange

P value intra-groupBaseline Endpoint

Meanchange

P value intra-group P value inter-group

Treatmentdifference

Serum TAG (mmoll) 1middot81 1middot09 1middot83 1middot37 +0middot03 0middot98 0middot848 1middot76 1middot25 1middot72 1middot37 minus0middot04 0middot68 0middot241 0middot628 +0middot07 1middot18Serum total cholesterol (mmoll) 5middot44 1middot12 5middot38 1middot12 minus0middot06 0middot58 0middot395 5middot45 1middot13 5middot38 1middot09 minus0middot08 0middot55 0middot257 0middot874 +0middot02 0middot89Serum HDL-cholesterol (mmoll) 1middot39 0middot38 1middot36 0middot37 minus0middot03 0middot19 0middot238 1middot38 0middot34 1middot38 0middot35 minus0middot00 0middot14 0middot929 0middot406 minus0middot03 0middot25Serum LDL-cholesterol (mmoll) 3middot45 0middot90 3middot41 0middot91 minus0middot04 0middot43 0middot459 3middot52 0middot95 3middot38 0middot88 minus0middot14 0middot41 0middot008 0middot193 +0middot10 0middot63Serum apo B (gl) 1middot05 0middot26 1middot04 0middot25 minus0middot02 0middot12 0middot257 1middot05 0middot26 1middot04 0middot25 minus0middot02 0middot12 0middot233 0middot864 +0middot00 0middot18Serum apo A1 (gl) 1middot63 0middot28 1middot60 0middot26 minus0middot03 0middot17 0middot128 1middot62 0middot26 1middot60 0middot27 minus0middot02 0middot13 0middot240 0middot824 minus0middot01 0middot23Plasma glucose (mmoll) 5middot08 0middot68 5middot11 0middot58 +0middot02 0middot47 0middot526 5middot18 0middot63 5middot13 0middot71 minus0middot03 0middot51 0middot671 0middot400 +0middot07 0middot71Serum insulin (pmoll) 47middot82 33middot62 46middot60 35middot86 minus1middot22 24middot48 0middot649 51middot15 38middot75 46middot39 38middot85 minus4middot75 26middot14 0middot079 0middot197 +3middot53 39middot16HOMA IR index 1middot57 1middot34 1middot51 1middot32 minus0middot05 0middot92 0middot911 1middot72 1middot42 1middot52 1middot41 minus0middot17 0middot99 0middot071 0middot226 +0middot13 1middot41HbA1c () 5middot66 0middot43 5middot68 0middot45 +0middot02 0middot19 0middot366 5middot70 0middot42 5middot66 0middot38 minus0middot03 0middot18 0middot146 0middot105 +0middot05 0middot27

HOMA IR homoeostasis model assessment of insulin resistance The two groups did not differ significantly with regard to any of the variables at baseline (paired Studentrsquos t tests or Wilcoxon signed-rank tests)

1272VBruumlllet

Table 6 Adhesion molecules parameters of oxidation and inflammation and vascular testing in the total study group (n 68) during the 6-week supplementation with quercetin or placebo(Mean values and standard deviations)

Serum endothelin-1 (pgml) 2middot22 0middot74 2middot25 0middot74 +0middot03 0middot46 0middot639 2middot09 0middot71 2middot25 0middot78 +0middot16 0middot52 0middot014 0middot129 minus0middot13 0middot71Serum sE-selektin (ngml) 36middot2 13middot6 37middot1 13middot7 +0middot9 5middot1 0middot144 36middot7 13middot8 36middot9 14middot0 +0middot2 4middot8 0middot712 0middot441 +0middot7 7middot3Serum sVCAM-1 (ngml) 581middot0 161middot9 571middot6 143middot4 minus9middot3 99middot7 0middot444 572middot5 152middot3 595middot4 155middot8 +22middot9 99middot9 0middot063 0middot055 minus32middot2 135middot8Serum sICAM-1 (ngml) 205middot7 54middot2 197middot5 48middot1 minus8middot2 17middot2 lt0middot001 202middot7 53middot0 199middot8 51middot6 minus2middot9 26middot7 0middot378 0middot219 minus5middot3 30middot7Plasma oxLDL (ngml) 408middot2 348middot8 406middot0 300middot8 minus2middot2 202middot7 0middot859 371middot9 236middot4 386middot9 221middot1 +15middot1 114middot7 0middot342 0middot352 minus17middot3 235middot7Plasma ADMA (micromoll) 0middot57 0middot16 0middot59 0middot15 +0middot01 0middot15 0middot530 0middot60 0middot21 0middot58 0middot15 minus0middot02 0middot18 0middot439 0middot266 +0middot03 0middot21L-ArginineADMA-ratio 146middot6 66middot8 147middot8 55middot3 +1middot2 73middot6 0middot896 141middot1 57middot8 144middot8 51middot8 +3middot7 54middot8 0middot577 0middot824 minus2middot6 94middot4Serum ACE (Ul) 38middot2 19middot2 38middot4 20middot2 +0middot2 7middot0 0middot800 38middot3 19middot5 39middot3 19middot8 +1middot1 6middot8 0middot198 0middot718 minus0middot9 10middot9Serum hs-CRP (mgl) 2middot20 1middot99 2middot21 2middot05 +0middot02 2middot17 0middot904 2middot24 2middot33 2middot81 3middot61 +0middot58 3middot33 0middot448 0middot283 minus0middot56 4middot04Urinary 8-iso-PGF2αcreatinine (pgmg)

198middot7 160middot5 216middot8 156middot7 +5middot8 177middot8 0middot183 236middot6 293middot6 187middot1 132middot9 minus56middot2 316middot3 0middot848 0middot552 ndash17middot9 300middot6

Urinary 23-dinor-15-F2t-IsoPcreatinine (pgmg)

644middot8 342middot4 645middot7 393middot6 +0middot9 257middot8 0middot608 664middot5 396middot0 669middot1 370middot4 +4middot3 259middot8 0middot788 0middot984 minus1middot0 390middot1

RHI (EndoPAT) 1middot90 0middot60 1middot89 0middot56 minus0middot01 0middot55 0middot911 1middot91 0middot57 1middot88 0middot48 minus0middot04 0middot66 0middot650 0middot762 +0middot03 0middot69AI (EndoPAT)dagger 8middot35 21middot89 8middot44 21middot91 +0middot08 10middot59 0middot957 6middot63 17middot35 7middot44 20middot98 +0middot81 10middot04 0middot578 0middot733 minus0middot73 14middot71

ACE angiotensin-converting enzyme ADMA asymmetric dimethylarginine AI augmentation index hs-CRP high-sensitive C-reactive protein IsoP isoprostanes oxLDL oxidised LDL RHI reactive hyperaemia index sICAM-1 solubleintercellular adhesion molecule 1 sVCAM-1 soluble vascular cell adhesion molecule 1

The two groups did not differ significantly with regard to any of the variables at baseline (paired Studentrsquos t tests or Wilcoxon signed-rank tests) EndoPAT data were obtained in a subgroup of forty-eight participantsdagger Corrected for heart rate and normed to 75 bpm

Effects

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re1273

(L-arginineADMA) serum ACE and serum CRP Quercetin andplacebo did not significantly affect endothelial function (RHIand AI) (Table 6) In addition plasma oxLDL and urinaryexcretion of 8-iso-PGF2α and 23-dinor-15-F2t-IsoP were notsignificantly changed by quercetin or placebo treatment in thetotal study group (Table 6)In the subgroup of hypertensive patients neither quercetin

nor placebo significantly affected serum endothelin-1 sE-selectin sVCAM-1 plasma ADMA serum ACE and CRP (datanot in Tables) In addition plasma oxLDL and urinary F2-IsoPwere not significantly changed by quercetin or placebo treat-ment in the subgroup of hypertensives (data not in Tables) Inthe subgroup of hypertensive patients quercetin and placebosignificantly decreased serum sICAM-1 concentrations frombaseline to a similar extent (quercetin minus9middot3 (SD 14middot8) ngmlP= 0middot002 placebo minus8middot6 (SD 15middot9) ngml P= 0middot007 treatmentdifference minus3middot5 (SD 17middot5) ngml P= 0middot584) (data not in Tables)

Correlations between blood pressure and biomarkers ofinflammationendothelial function

In the total study group and also in the subgroup of hypertensivepatients baseline SBP and DBP did not significantly correlatewith baseline biomarkers of inflammation and endothelial func-tion (CRP endothelin-1 sE-selectin sVCAM-1 sICAM-1 ADMARHI and AI) In addition changes in BP variables did not sig-nificantly correlate with changes in biomarkers of inflammationand endothelial function neither in the total study group nor inthe subgroup of hypertensives (data not shown)

Discussion

The aim of this double-blinded placebo-controlled cross-overintervention study was to systematically investigate the effectsof quercetin on arterial BP (primary variable) endothelialfunction and further CVD risk markers in overweight-to-obeseindividuals with hypertension Our major finding was thatquercetin supplementation for 6 weeks in a supra-nutritionaldosage significantly reduced 24 h systolic ABP in hypertensiveparticipants In contrast to our hypotheses we observed noeffect of quercetin supplementation on secondary variablessuch as endothelial function including RHI sE-selectinsVCAM-1 ADMA and endothelin-1 In addition no effects onparameters of inflammation oxidative stress and lipid andglucose metabolism were observed We used a moderate supra-nutritional but non-pharmacological dose of quercetin fromonion skin extract as these data should provide a rational basisfor the development of functional foods

Blood pressure

Quercetin significantly reduced the mean 24 h SBP by 3middot6(SD 8middot2)mmHg in hypertensive participants but not inpre-hypertensive individuals suggesting that a threshold ofelevated BP might be required to detect a BP-lowering effectof quercetin The significant interaction effect between stage ofhypertension and treatment assignment confirms this In contrast to

our previous trial(7) we found no significant effects of chronicquercetin supplementation on office SBP At first glance thisfinding is surprising Our study design (eg quercetin dose inter-vention period) was similar to our earlier study In addition ourparticipants (pre-hypertensive patients with abdominal fat dis-tribution) and sample size were well chosen in consideration withthe primary objective of the trial In accordance with our previousstudy(7) we observed a relatively high inter-individual variation inBP-lowering effects of quercetin In both studies only 44 to 51 ofthe participants showed a decrease in systolic office BP despitethe fact that compliance with supplementation in both trials wasvery high (94ndash98) Compliance was confirmed by a markedincrease in plasma quercetin concentrations (final concentrationsof both trials 0middot3ndash0middot45 micromoll) and also in the monomethylatedderivatives isorhamnetin and tamarixetin However in both trialschanges in BP were not significantly correlated with plasma totalquercetin isorhamnetin andor tamarixetin These findings indi-cate that in humans the BP-lowering effects of chronic quercetinsupplementation are difficult to predict In addition it is not pos-sible to deduce a minimum plasma concentration or quercetindose required for a specific biological activity In this regard it isvery likely that the plasma concentration of total quercetin doesnot necessarily reflect the concentration at the target sites Similarhigh inter-individual variance in BP-lowering effects of quercetincan be observed in the study of Edwards et al(13) in human sub-jects treated with pharmacological doses of 730mgd quercetin for4 weeks The authors illustrated individual subject responses dur-ing each supplementation phase (placebo quercetin) in theirpublication however they did not discuss these results

Overall the quercetin-induced reductions in SBP observed in thepresent trial and previously (range minus2middot6 to minus8middot8mmHg)(7131424)

are similar to those experienced following current recommendedlifestyle modifications to reduce elevated BP (eg reducing sodiumintake and body weight increasing physical activity)(3738) A 3middot6mmHg decrease in SBP as observed in the present trial would beclinically meaningful when considered at the population levelparticularly in view of the large population of people with pre-hypertension and stage I hypertension(39) In addition similareffects have been found for other dietary flavonoids especially forflavonols from cocoa products(4041)

Endothelial function inflammation and oxidation

The first mechanism of action we explored was that quercetin-induced reductions in BP are secondary to an improvement invascular endothelial function Rationale for this hypotheses wasbased on data from (i) normotensive humans wherein acuteadministration of 200 mg quercetin increased plasma quercetinand NO metabolite concentrations while decreasing endothelin-1(42) (ii) hypertensive rats in which quercetin attenuatedhypertension andor vascular dysfunction in a NO-dependentmanner(43ndash45) and (iii) in vitro studies wherein quercetindecreased cellular production of endothelin-1(4647) andendothelial-derived adhesion molecules(4849) In the presentstudy biomarkers of endothelial function (plasma endothelin-1sE-selectin sVCAM-1 ADMA RHI and AI) were unaffected bythe quercetin treatment Therefore these markers cannotexplain a possible relationship between quercetin and BP

However in view of the only modest decrease in SBP ourstudy was probably not suited to demonstrate small changes inthese markers In addition baseline PAT indices andendothelial-derived adhesion molecules did not correlate withBP emphasising that factors regulating endothelial functiondiffer at least in part from those regulating BPIn contrast to previous in vitro(89) and in vivo results

obtained in animal models(49ndash51) showing an anti-inflammatoryeffect of quercetin quercetin supplementation did not reduceserum concentrations of CRP This may in part be explained bythe duration of the intervention andor the quercetin dosageandor the low-grade inflammatory state of our participantswhich were insufficient to elicit measurable effects In agree-ment with this finding and consistent with earlier studies inhumans(132352) no changes in biomarkers of in vivo lipidperoxidation (plasma oxLDL and urinary IsoP) were observedfollowing quercetin administration This may be attributed to analready sufficient antioxidant defence status of our hypertensivesubjects All participants had an adequate dietary intake ofessential antioxidants (vitamins E C β-carotene) In additionthey did not report smoking or excessive physical exercise

Angiotensin-converting enzyme

The second mechanism we hypothesised was that chronicquercetin supplementation decreased arterial BP in hypertensivepatients by decreasing ACE activity Rationale for this hypotheseswas based on experimental studies demonstrating that quercetininhibits ACE in vitro(53) and on animal-based evidence showinga decrease in ACE activity after quercetin treatment in rats(5455)For example Mackraj et al(54) compared the long-termantihypertensive effects of captopril (ACE inhibitor) with those ofquercetin in Dahl salt-sensitive rats that were given daily injectionsof captopril quercetin or vehicle Although BP increased in vehicle-treated Dahl rats it was significantly decreased compared withbaseline in both quercetin- and captopril-treated groups Thedecrease in BP occurred in parallel with the down-regulation of theangiotensin-I receptor in the kidney increased urine volume andincreased urinary sodium excretion thus providing a potentialmechanism for the long-term BP-lowering effects of quercetin(15)However although chronic quercetin administration decreased24 h ABP in our hypertensive patients we found no decreasein plasma ACE activity Our results are in accordance withdata recently reported by Larson et al(56) showing that acutequercetin-induced reductions in BP in hypertensive individualswere not secondary to a reduced ACE activity

Lipid and glucose metabolism

In the present study chronic quercetin supplementation for6 weeks did not affect fasting serum concentrations of totalcholesterol LDL-cholesterol and HDL-cholesterol TAG andapolipoproteins supporting previous data in metabolicallyhealthy participants(2357) in overweight-to-obese patients withmetabolic syndrome traits(7) in men with different apoEisoforms(52) and in women with type 2 diabetes mellitus(14) Incontrast Lee et al(58) found that supplementation with quer-cetin (100mgd) for 10 weeks significantly reduced fasting

serum concentrations of total cholesterol and LDL-cholesteroland significantly increased serum HDL-cholesterol in malesmokers In addition supplements of quercetin-rich red grapejuice(59) and grape powder(60) favourably influenced plasmalipid profiles in human subjects These inconclusive results maybe attributed to the duration of quercetin administration thebaseline characteristics of the study participants and the dosageof the ingested quercetin Experimental studies in rat liver cellsdemonstrated that quercetin at high concentrations (eg 25micromoll) may be involved in lipid metabolism by reducinghepatic fatty acid TAG and cholesterol synthesis(6162)

In accordance with previous human studies(713245260) querce-tin did not affect fasting plasma glucose serum insulin HOMA IRor HbA1c in our hypertensive patients although Lee et al(58)

demonstrated a slight decrease (minus3middot9) in fasting serum glucoseafter quercetin treatment Our results are in contrast to experi-mental reports demonstrating the hypoglycaemic effects of highquercetin doses (ge10mgkg of body weight) in animal models(eg obese Zucker Rats)(10ndash12)

Strengths and limitations

The major strengths of our study are the double-blinded placebo-controlled cross-over design the relatively large sample size thehigh compliance to treatment the low dropout rate and theexamination of numerous markers of vascular function Howeverthis study also has a few potential limitations First we administereda quercetin-rich onion skin extract instead of pure quercetin(quercetin dihydrate) as we did in our previous trials(72324) Onionskins are rich in quercetin aglycone(63) and the bioavailability ofquercetin from capsules filled with onion skin extract powder wasshown to be significantly higher than that from capsules filled withquercetin dihydrate (C Burak V Bruumlll P Langguth BF Zimmer-mann B Stoffel-Wagner P Stehle S Wolffram S Egert unpublishedresults) Thus we decided to use a quercetin-rich onion skin extractfor the present trial We characterised the polyphenol spectrum ofthe extract (Table 1) but we cannot exclude that other unknowncomponents in the onion skin extract may have influenced ourfindings Thus strictly the conclusion of our study is only true forquercetin-rich onion skin extract but not for pure quercetinSecond we conducted an explorative data analysis All parameterswere analysed for the whole study group and also for the subgroupof patients with hypertension Due to the multiple test situationswe cannot fully exclude that the significant effect on 24 h SBP inthe subgroup of hypertensives was a chance finding On the otherhand we do not think that corrections for multiple testing aremeaningful in the context of explorative data analysis(64)

Conclusion

Regular ingestion of a supra-nutritional dose of 162mgd quercetinfrom onion skin extract did not affect BP and endothelial functionin the whole study population of pre-hypertensive and stage 1hypertensive overweight-to-obese subjects In the subgroup ofhypertensives quercetin was capable of decreasing 24 h SBPsuggesting a cardioprotective effect of quercetin but without effectson mechanistic parameters Thus the mechanisms responsible forthe BP-lowering effect of quercetin remain elusive

Acknowledgements

This study was supported by the German Research Foundation(S E grant no EG2923-1) The German Research Foundationhad no role in the design analysis or writing of this articleV B P S and S E designed the study together with G N

and C M who were the medical advisors V B C B and S Erecruited the subjects and conducted the study B A performedthe blinding procedure P L prepared the capsules V B C BB S-W S W S N B F Z and S E participated in datacollection and analysis V B C B and S E performed thestatistical calculations with support from R F V B P S and SE wrote the manuscript VB and S E had primary responsi-bility for the final content All authors read and approved thefinal manuscriptThere are no conflicts of interest

References

1 Crozier A Jaganath IB amp Clifford MN (2009) Dietary phenolicschemistry bioavailability and effects on health Nat Prod Rep26 1001ndash1043

2 Erdman JW Jr Balentine D Arab L et al (2007) Flavonoidsand Heart Health Proceedings of the ILSI North AmericaFlavonoids Workshop May 31-June 1 2005 Washington DCJ Nutr 137 718Sndash737S

3 Scalbert A amp Williamson G (2000) Dietary intake andbioavailability of polyphenols J Nutr 130 2073Sndash2085S

4 Wang X Ouyang YY Liu J et al (2013) Flavonoid intake andrisk of CVD a systematic review and meta-analysis of pro-spective cohort studies Br J Nutr 111 1ndash11

5 Hubbard GP Wolffram S Lovegrove JA et al (2004) Ingestionof quercetin inhibits platelet aggregation and essentialcomponents of the collagen-stimulated platelet activationpathway in humans J Thromb Haemost 2 2138ndash2145

6 Hubbard GP Wolffram S de Vos R et al (2006) Ingestion ofonion soup high in quercetin inhibits platelet aggregationand essential components of the collagen-stimulated plateletactivation pathway in man a pilot study Br J Nutr 96 482ndash488

7 Egert S Bosy-Westphal A Seiberl J et al (2009) Quercetinreduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects witha high-cardiovascular disease risk phenotype a double-blinded placebo-controlled cross-over study Br J Nutr 1021065ndash1074

8 Boots AW Wilms LC Swennen EL et al (2008) In vitro andex vivo anti-inflammatory activity of quercetin in healthyvolunteers Nutrition 24 703ndash710

9 Nair MP Mahajan S Reynolds JL et al (2006) The flavonoidquercetin inhibits proinflammatory cytokine (tumor necrosisfactor alpha) gene expression in normal peripheral bloodmononuclear cells via modulation of the NF-kappabeta system Clin Vaccine Immunol 13 319ndash328

10 Rivera L Moron R Sanchez M et al (2008) Quercetinameliorates metabolic syndrome and improves theinflammatory status in obese zucker rats Obesity (SilverSpring) 16 2081ndash2087

11 Jeong SM Kang MJ Choi HN et al (2012) Quercetinameliorates hyperglycemia and dyslipidemia and improvesantioxidant status in type 2 diabetic dbdb mice Nutr ResPract 6 201ndash207

12 Kobori M Masumoto S Akimoto Y et al (2011) Chronicdietary intake of quercetin alleviates hepatic fat accumulation

associated with consumption of a Western-style diet in C57BL6J mice Mol Nutr Food Res 55 530ndash540

13 Edwards RL Lyon T Litwin SE et al (2007) Quercetinreduces blood pressure in hypertensive subjects J Nutr 1372405ndash2411

14 Zahedi M Ghiasvand R Feizi A et al (2013) Does quercetinimprove cardiovascular risk factors and inflammatory bio-markers in women with type 2 diabetes a double-blind ran-domized controlled clinical trial Int J Prev Med 4 777ndash785

15 Larson AJ Symons JD amp Jalili T (2012) Therapeutic potential ofquercetin to decrease blood pressure review of efficacy andmechanisms Adv Nutr 3 39ndash46

16 Zawadzki MJ Graham JW amp Gerin W (2012) Increasing thevalidity and efficiency of blood pressure estimates usingambulatory and clinic measurements and modern missingdata methods Am J Hypertens 25 764ndash769

17 Myers MG amp Godwin M (2007) Automated measurement ofblood pressure in routine clinical practice J Clin Hypertens(Greenwich) 9 267ndash270

18 Chobanian AV Bakris GL Black HR et al (2003) The SeventhReport of the Joint National Committee on PreventionDetection Evaluation and Treatment of High Blood Pressurethe JNC 7 report JAMA 289 2560ndash2572

19 Alberti KG Zimmet P amp Shaw J (2005) The metabolic syn-dromendasha new worldwide definition Lancet 366 1059ndash1062

20 Linseisen J Radtke J amp Wolfram G (1997) Flavonoid intake ofadults in a Bavarian subgroup of the national foodconsumption survey Z Ernahrungswiss 36 403ndash412

21 Zamora-Ros R Forouhi NG Sharp SJ et al (2014) Dietaryintakes of individual flavanols and flavonols are inverselyassociated with incident type 2 diabetes in Europeanpopulations J Nutr 144 335ndash343

22 Egert S Wolffram S Schulze B et al (2012) Enrichedcereal bars are more effective in increasing plasma quercetincompared with quercetin from powder-filled hard capsulesBr J Nutr 107 539ndash546

23 Egert S Wolffram S Bosy-Westphal A et al (2008) Dailyquercetin supplementation dose-dependently increasesplasma quercetin concentrations in healthy humans J Nutr138 1615ndash1621

24 Egert S Boesch-Saadatmandi C Wolffram S et al (2010)Serum lipid and blood pressure responses to quercetin vary inoverweight patients by apolipoprotein E genotype J Nutr140 278ndash284

25 Pickering TG Hall JE Appel LJ et al (2005) Recommenda-tions for blood pressure measurement in humans andexperimental animals Part 1 blood pressure measurement inhumans a statement for professionals from the Subcommitteeof Professional and Public Education of the American HeartAssociation Council on High Blood Pressure ResearchHypertension 45 142ndash161

26 Axtell AL Gomari FA amp Cooke JP (2010) Assessing endothelialvasodilator function with the Endo-PAT 2000 J Vis Exp issue44 2167

27 Kuvin JT Patel AR Sliney KA et al (2003) Assessment ofperipheral vascular endothelial function with finger arterialpulse wave amplitude Am Heart J 146 168ndash174

28 Nohria A Gerhard-Herman M Creager MA et al (2006)Role of nitric oxide in the regulation of digital pulsevolume amplitude in humans J Appl Physiol (1985) 101545ndash548

29 Bonetti PO Pumper GM Higano ST et al (2004) Noninvasiveidentification of patients with early coronary atherosclerosisby assessment of digital reactive hyperemia J Am Coll Cardiol44 2137ndash2141

30 Hamburg NM Keyes MJ Larson MG et al (2008) Cross-sectionalrelations of digital vascular function to cardiovascular risk factorsin the Framingham Heart Study Circulation 117 2467ndash2474

31 Sun SS Chumlea WC Heymsfield SB et al (2003) Developmentof bioelectrical impedance analysis prediction equations for bodycomposition with the use of a multicomponent model for use inepidemiologic surveys Am J Clin Nutr 77 331ndash340

32 Matthews DR Hosker JP Rudenski AS et al (1985) Home-ostasis model assessment insulin resistance and beta-cellfunction from fasting plasma glucose and insulinconcentrations in man Diabetologia 28 412ndash419

33 Fuumlrst P Pollack L Graser TA et al (1990) Appraisal of fourpre-column derivatization methods for the high-performanceliquid chromatographic determination of free amino acids inbiological materials J Chromatogr 499 557ndash569

34 Bieger J Cermak R Blank R et al (2008) Tissue distributionof quercetin in pigs after long-term dietary supplementationJ Nutr 138 1417ndash1420

35 USDepartment of Agriculture (2013) USDA database for theflavonoid content of selected foods release 31 httpwwwars usda govServicesdocs htmdocid=6231

36 Kenward MG amp Jones B (1987) The analysis of data from2times2 cross-over trials with baseline measurements Stat Med 6911ndash926

37 Appel LJ Brands MW Daniels SR et al (2006) Dietaryapproaches to prevent and treat hypertension a scientificstatement from the American Heart Association Hypertension47 296ndash308

38 Whelton PK Appel LJ Sacco RL et al (2012) Sodium bloodpressure and cardiovascular disease further evidence sup-porting the American Heart Association sodium reductionrecommendations Circulation 126 2880ndash2889

39 Lewington S Clarke R Qizilbash N et al (2002) Age-specificrelevance of usual blood pressure to vascular mortality ameta-analysis of individual data for one million adults in 61prospective studies Lancet 360 1903ndash1913

40 Ellinger S Reusch A Stehle P et al (2012) Epicatechiningested via cocoa products reduces blood pressure inhumans a nonlinear regression model with a Bayesianapproach Am J Clin Nutr 95 1365ndash1377

41 Hooper L Kay C Abdelhamid A et al (2012) Effects ofchocolate cocoa and flavan-3-ols on cardiovascular health asystematic review and meta-analysis of randomized trials AmJ Clin Nutr 95 740ndash751

42 Loke WM Hodgson JM Proudfoot JM et al (2008) Puredietary flavonoids quercetin and (minus)-epicatechin augmentnitric oxide products and reduce endothelin-1 acutely inhealthy men Am J Clin Nutr 88 1018ndash1025

43 Duarte J Jimenez R OrsquoValle F et al (2002) Protective effectsof the flavonoid quercetin in chronic nitric oxide deficient ratsJ Hypertens 20 1843ndash1854

44 Galindo P Rodriguez-Gomez I Gonzalez-Manzano S et al(2012) Glucuronidated quercetin lowers blood pressure inspontaneously hypertensive rats via deconjugation PLOS ONE7 e32673

45 Sanchez M Galisteo M Vera R et al (2006) Quercetindownregulates NADPH oxidase increases eNOS activity andprevents endothelial dysfunction in spontaneouslyhypertensive rats J Hypertens 24 75ndash84

46 Ruef J Moser M Kubler W et al (2001) Induction ofendothelin-1 expression by oxidative stress in vascularsmooth muscle cells Cardiovasc Pathol 10 311ndash315

47 Zhao X Gu Z Attele AS et al (1999) Effects of quercetin onthe release of endothelin prostacyclin and tissue plasminogen

activator from human endothelial cells in culture J Ethno-pharmacol 67 279ndash285

48 Ying B Yang T Song X et al (2008) Quercetin inhibits IL-1beta-induced ICAM-1 expression in pulmonary epithelial cellline A549 through the MAPK pathways Mol Biol Rep 361825ndash1832

49 Kleemann R Verschuren L Morrison M et al (2011)Anti-inflammatory anti-proliferative and anti-atheroscleroticeffects of quercetin in human in vitro and in vivo modelsAtherosclerosis 218 44ndash52

50 Boesch-Saadatmandi C Wagner AE Wolffram S et al (2012)Effect of quercetin on inflammatory gene expression in miceliver in vivo - role of redox factor 1 miRNA-122 andmiRNA-125b Pharmacol Res 65 523ndash530

51 Mahmoud MF Hassan NA El Bassossy HM et al (2013)Quercetin protects against diabetes-induced exaggeratedvasoconstriction in rats effect on low grade inflammationPLOS ONE 8 e63784

52 Pfeuffer MA Auinger A Bley U et al (2013) Effect of quer-cetin on traits of the metabolic syndrome endothelial functionand inflammatory parameters in men with different APOEisoforms Nutr Metab Cardiovasc Dis 23 403ndash409

53 Loizzo MR Said A Tundis R et al (2007) Inhibition ofangiotensin converting enzyme (ACE) by flavonoids isolatedfrom Ailanthus excelsa (Roxb) (Simaroubaceae) Phytother Res21 32ndash36

54 Mackraj I Govender T amp Ramesar S (2008) The anti-hypertensive effects of quercetin in a salt-sensitive model ofhypertension J Cardiovasc Pharmacol 51 239ndash245

55 Hackl LP Cuttle G Dovichi SS et al (2002) Inhibition ofangiotesin-converting enzyme by quercetin alters the vascularresponse to brandykinin and angiotensin I Pharmacology 65182ndash186

56 Larson A Witman MA Guo Y et al (2012) Acute quercetin-induced reductions in blood pressure in hypertensive indivi-duals are not secondary to lower plasma angiotensin-converting enzyme activity or endothelin-1 nitric oxideNutr Res 32 557ndash564

57 Conquer JA Maiani G Azzini E et al (1998) Supplementationwith quercetin markedly increases plasma quercetin con-centration without effect on selected risk factors for heartdisease in healthy subjects J Nutr 128 593ndash597

58 Lee KH Park E Lee HJ et al (2011) Effects of daily quercetin-rich supplementation on cardiometabolic risks in male smo-kers Nutr Res Pract 5 28ndash33

59 Castilla P Echarri R Davalos A et al (2006) Concentrated redgrape juice exerts antioxidant hypolipidemic and antiin-flammatory effects in both hemodialysis patients and healthysubjects Am J Clin Nutr 84 252ndash262

60 Zern TL Wood RJ Greene C et al (2005) Grape polyphenolsexert a cardioprotective effect in pre- and postmenopausalwomen by lowering plasma lipids and reducingoxidative stress J Nutr 135 1911ndash1917

61 Gnoni GV Paglialonga G amp Siculella L (2009) Quercetininhibits fatty acid and TAG synthesis in rat-liver cells Eur JClin Invest 39 761ndash768

62 Glasser G Graefe EU Struck F et al (2002) Comparison ofantioxidative capacities and inhibitory effects on cholesterolbiosynthesis of quercetin and potential metabolites Phyto-medicine 9 33ndash40

63 Wiczkowski W Romaszko J Bucinski A et al (2008) Quercetinfrom shallots (Allium cepa L var aggregatum) is morebioavailable than its glucosides J Nutr 138 885ndash888

64 Rothman KJ (1990) No adjustments are needed for multiplecomparisons Epidemiology 1 43ndash46

Reproduced with permission of the copyright owner Further reproduction prohibited withoutpermission

cS0007114515002950a_13151pdf

Effects of a quercetin-rich onion skin extract on 24ampx2009h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-)hypertension a randomised double-blinded placebo-controlled cross-overtrial

Methods

Subjects

Study design

Fig 1Flow diagram of participants ABP ambulatory blood pressure BP blood pressure

Measurements

Office blood pressure and heart rate

24ampx2009h ambulatory blood pressure monitoring

Vascular testing

Anthropometrics

Bloodampx002Furine sample processing and analysis

Table 1Flavonoid analysis in onion skin extract powderampx002A(Mean values and standard deviations)

Self-reported dietary intake of energy nutrients and quercetin


Results

Subject characteristics at screening compliance and dietary intake

Body weight waist and hip circumference body composition and potential side-effects

Ambulatory blood pressure monitoring and office blood pressure

Table 2Subject characteristics and blood parameters at screening(Mean values and standard deviations)

Table 3Measurements of the 24ampx2009h ambulatory blood pressure and office blood pressure in the total study group during the 6-week dietary supplementation with quercetin or placeboampx002A(Mean values and standard deviations)

Serum lipids lipoproteins apolipoproteins glucose and insulin

Soluble adhesion molecules asymmetric dimethylarginine angiotensin-converting enzyme C-reactive protein endothelial function and oxidation

Fig 2Fasting plasma concentrations of quercetin (a) (n 68) and total flavonols (b) (n 68) before and after the 6-week supplementation with quercetin (162ampx2009mgampx002Fd ampx25A0) or placebo (ampx25A1) Values are means and standard deviations repr

Table 4Measurements of the 24ampx2009h ambulatory blood pressure and office blood pressure in the subgroup of hypertensive patients during the 6-week dietary supplementation with quercetin or placeboampx002A(Mean values and standard deviations)

Table 5Fasting lipids lipoproteins apolipoproteins insulin glucose HbA1c and HOMA IR Index in the total study group (n 68) during the 6-week dietary supplementation with quercetin or placeboampx002A(Mean values and standard deviations)

Table 6Adhesion molecules parameters of oxidation and inflammation and vascular testing in the total study group (n 68) during the 6-week supplementation with quercetin or placeboampx002A(Mean values and standard deviations)

Correlations between blood pressure and biomarkers of inflammationampx002Fendothelial function

Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

supplementation of quercetin may reduce platelet aggrega-tion(56) and plasma concentrations of atherogenic oxidised LDL(oxLDL)(7) In vitro studies suggest that high concentrations ofquercetin (gt1 microM) have anti-inflammatory effects(89) Studies inanimal models (eg obese Zucker rats) suggest beneficialeffects of quercetin on obesity-associated metabolic disordersincluding insulin resistance and dyslipidaemia(10ndash12) Werecently showed that in patients with high CVD risk phenotypechronic supplementation with a supra-nutritional dose of150mgd quercetin significantly reduced systolic blood pres-sure (SBP)(7) Similar findings have been reported by Edwardset al(13) in hypertensive patients and recently by Zahediet al(14) in women with type 2 diabetes mellitus although withpharmacological quercetin doses (500 and 730 mgd) Althoughseveral pathways have been suggested the mechanisms bywhich quercetin possibly affects blood pressure (BP) are notwell-understood These pathways include (i) improvement ofvascular function in an endothelium-dependent orendothelium-independent manner (ii) decrease in oxidativestress andor (iii) interference with the reninndashangiotensinndashaldosterone system(15)One limitation in the interpretation of the BP-lowering effect

of chronic quercetin supplementation is that all human studiespublished to date including our own trial(7) only measured theoffice (clinic) BP in the resting state (typically in the morningwhile fasting) and did not integrate an ambulatory bloodpressure (ABP) monitoring ABP monitoring is considered thegold standard for BP measurement compared with clinic BPmeasurements as it is superior in terms of reliability andvalidity(1617) The superior predictive power of ABP monitoringis probably not only due to its higher number of readingswhich increases the reliability of the measurement but alsodue to its ability to capture the impact of stressors and otherenvironmental factors that occur in daily life and are likely toaffect BP(16) To the best of our knowledge no previous studyhas examined the effects of quercetin on 24 h ABP profiles thusfar Therefore the aim of the present double-blinded placebo-controlled cross-over trial was to systematically investigate theeffects of quercetin on arterial BP (office BP and 24 h ABPprofiles) in adults with pre-hypertension and stage I hyperten-sion and to explore mechanisms involved in the BP-loweringefficacy of quercetin Furthermore effects of quercetin on lipidand glucose metabolism were investigated

Methods

Subjects

Overweight-to-obese subjects were recruited from the com-munity of the city of Bonn Germany via public postings flyersand advertisements in the local newspaper From a total of 500interested subjects 154 individuals aged 25ndash65 years with a BMIof 25ndash35 kgm2 attended a screening which included physicalassessments (body height and weight resting BP heart ratewaist and hip circumference) clinical assessments (liver func-tion serum lipids and lipoproteins glucose and uric acidhaematology high-sensitive C-reactive protein (hs-CRP))medical history and a dietary questionnaire

Participants were included if they had the following traits ofthe metabolic syndrome (i) central obesity (waist circumferencege94 cm for men and ge80 cm for women) (ii) pre-hypertension(ge120ndash139mmHg SBP andor ge80ndash89mmHg diastolic bloodpressure (DBP)) or stage I hypertension (ge140ndash159mmHgSBP andor ge90ndash99mmHg DBP) (iii) dyslipidaemia (fastingserum TAG concentrations ge1middot7mmoll andor serumconcentrations of HDL-cholesterol lt1middot0mmoll for men andlt1middot3mmoll for women) andor a proinflammatory state(hs-CRPge 2mgl)(1819) Main exclusion criteria were as followssmoking diagnosed type 2 diabetes mellitus liver gastro-intestinal or diagnosed inflammatory diseases a history ofcardiovascular events untreated thyroid dysfunction cancerrecent major surgery or illness pregnancy or breast feedingalcohol abuse consumption of polyphenol-rich supplementsparticipation in a weight loss programme and Raynaudrsquossyndrome

A total of seventy subjects (thirty-five male thirty-five female)were included into the study During the first interventionperiod two subjects dropped out for personal reasons Onlydata from the remaining sixty-eight subjects (thirty-four malethirty-four female) who completed the entire interventionstudy were included in the analysis and are subsequentlyreported The participant flow from the initial screening to finalanalysis is shown in Fig 1

The study protocol was explained in detail to all the participantswho gave their written informed consent at the beginning of thestudy The study protocol was approved by the ethics committee ofthe Medical Faculty of the Rheinische Friedrich-Wilhelms-Universitaumlt Bonn Germany and was in accordance with theHelsinki declaration The trial was registered at wwwgermanctrde and httpappswhointtrialsearch as DRKS00000555

The subjects were instructed to maintain their habitualdiet physical activity levels lifestyle factors and body weightParticipants taking oral contraceptives (n 4 women) orantihypertensive (n 12) or thyroid drugs (n 9) were instructed tocontinue taking their medication without changes

Study design

This study was a double-blinded randomised placebo-controlled cross-over trial with 6-week treatment periodsseparated by a 6-week washout period Subjects were instruc-ted to take a total of three capsules per d one capsule with eachprincipal meal Two kinds of hard gelatin capsules ndash quercetinand placebo ndash were manufactured at the Institute of Pharmacyand Biochemistry Johannes Gutenberg University MainzQuercetin capsules were filled with onion skin extract powder(132 mgcapsule) placebo capsules contained mannitol(approximately 170mgcapsule) For the production of theonion skin extract powder onion skins were washed with waterand then extracted using ethanol Thereafter the extractionsolvent was removed by evaporation The resulting suspensionwas decanted and subsequently vacuum-dried The flavonoidcontents of the onion skin extract and of quercetin capsuleswere determined by HPLC with diode-array detection Theidentity of the flavonoids was confirmed by MSMS The resultsof quantification are shown in Table 1 The quercetin content of

(n 154)

Enrolment

Crossover

Allocation

Analyses

Measurements

(g100 g)

Compound Mean SD

Results

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

(n 154)

Enrolment

Crossover

Allocation

Analyses

Measurements

(g100 g)

Compound Mean SD

Results

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Measurements

(g100 g)

Compound Mean SD

Results

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Results

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Effects

ofquercetin

onbloodpressu

re1269

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Week 0 Week 6

dagger

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Quercetin Placebo

Effects

ofquercetin

onbloodpressu

re1271

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Meanchange

Treatmentdifference

1272VBruumlllet

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Effects

ofquercetin

onbloodpressu

re1273

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Discussion

Blood pressure

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Conclusion

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Acknowledgements

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

cS0007114515002950a_13151pdf


Methods

Subjects

Study design


Measurements



Vascular testing

Anthropometrics





Results













Discussion

Blood pressure





Conclusion

Acknowledgements

ACKNOWLEDGEMENTS

References

Documents

Effects of a quercetin-rich onion skin extract on 24h ...We investigated the effects of quercetin after regular intake on blood pressure (BP) in overweight-to-obese patients with pre-hypertension