Food and Chemical Toxicology 57 (2013) 161–169

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Food and Chemical Toxicology

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Lead, mercury, and cadmium in blood and their relation to diet amongSwedish adults

0278-6915/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.fct.2013.03.024

Abbreviations: Pb, lead; Hg, mercury; Cd, cadmium; OEMC, Occupational andEnvironmental Medicine Center; BMI, body mass index; B, blood; U, urine; CTQ,Centre de Toxicologie du Quebec; SD, standard deviation; SE, standard error.⇑ Corresponding author. Address: The National Food Agency, P.O. Box 622, SE-751

26 Uppsala, Sweden. Tel.: +46 18 17 55 00; fax: +46 18 10 58 48.E-mail address: per.ola.darnerud@slv.se (P.O. Darnerud).

Helena Bjermo a, Salomon Sand a, Cecilia Nälsén a, Thomas Lundh b, Heléne Enghardt Barbieri a,Monika Pearson a, Anna Karin Lindroos a, Bo A.G. Jönsson b, Lars Barregård c, Per Ola Darnerud a,⇑a National Food Agency, Uppsala, Swedenb Division of Occupational and Environmental Medicine, Lund University, Lund, Swedenc Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden

a r t i c l e i n f o

Article history:Received 18 December 2012Accepted 14 March 2013Available online 26 March 2013

Keywords:Heavy metalsLeadMercuryCadmiumDietBlood

a b s t r a c t

The aim of the present study was to examine the body burden of lead (Pb), mercury (Hg), and cadmium(Cd) in blood among Swedish adults and the association between blood levels, diet and other lifestyle fac-tors.

The study was based on a subgroup (n = 273) of the national survey Riksmaten 2010–2011 (4-day foodrecords and questionnaire). Lead, Hg, and Cd were measured in whole blood, and Cd additionally in urine,by mass or fluorescence spectrometry methods.

The median values (5–95th percentiles) of the metals in blood were as follows; Pb: 13.4 (5.8–28.6) lg/L, Hg: 1.13 (0.31–3.45) lg/L, and Cd: 0.19 (0.09–1.08) lg/L. All three metals increased with increasingage. Lead levels in blood were positively associated with intakes of game and alcohol, Hg was relatedto fish intake, and blood Cd related to smoking and low iron stores and to a low meat intake.

Body burdens of the studied metals were generally below health based reference values, but severalindividuals had blood Pb levels above the reference point for possible nephrotoxic and developmentalneurotoxic effects. As health effects cannot be excluded, individuals with high Pb exposure should aimat decreasing their body burden, both from food and from other exposure routes.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Toxic metals such as lead (Pb), mercury (Hg) and cadmium (Cd)are natural components of our earth crust. However, the environ-ment has been enriched by industrial processes, and man-madesources such as mining, industries, motor vehicle exhaust, and bat-teries contribute to the environmental levels and to human expo-sure. Even though the contribution from the man-made sourceshas decreased substantially, the environmental contamination willremain for many decades. Pb and Hg, and probably also Cd havedetrimental effects on the central nervous system in the develop-ing infant (Bellinger, 2008; Mendola et al., 2002; Kippler et al.,2012). Even if neurotoxicity is the most sensitive endpoint, Pbmay also affect blood pressure, kidney function, cause mutagenesisand have reproductive effects (Nordberg et al., 2007). Humans are

exposed to Pb by a number of contributing food sources, but alsoby drinking water and air, whereas in case of Hg there is one majorsource, namely fish (Florea and Busselberg, 2006; Martorell et al.,2011). The toxic effects of Cd are mainly affecting the kidneysand skeleton. Long-term exposure can cause renal tubular dysfunc-tion. In addition, Cd exposure may lead to osteoporosis, and themetal has been classified as a human carcinogen (Nordberg et al.,2007; Satarug and Moore, 2004). Diet is considered the mainsource of Cd intake among non-smokers (Skerfving et al., 1999),and especially food cultured in Cd-rich soil constitutes a majorsource for Cd (Satarug and Moore, 2004).

In Sweden, the body burdens of Pb and Hg are decreasing withtime whereas this is not evident for Cd levels (Barregard et al.,2010; Wennberg et al., 2006), for Cd levels perhaps with the excep-tion for smoking men. Thus, the dietary Cd exposure in Swedenseems to be unchanged (Wennberg et al., 2006) and in a marketbasket study from 2010, similar Cd exposures from food were re-ported in studies from 1987, 1999 and 2010 (NFA, 2012a). This factneeds further investigation, especially since the toxic effects onkidney and bone may be observed at lower Cd concentrations thanpreviously believed (Akesson et al., 2005; Ferraro et al., 2010; Eng-strom et al., 2011). At low urinary (U-) Cd levels, associations

162 H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169

between U-Cd and proteinuria may reflect renal physiology ratherthan toxicity of Cd (Chaumont et al., 2012; Akerstrom et al., 2013),but this problem does not occur for effects found on bone.

Due to the irreversible health effects of Pb, Hg, and Cd, primaryprevention is essential. It is therefore necessary to examine theexposure and body burden of these metals in the general popula-tion using biomarkers, and to obtain knowledge about the majorsources of the metals. The aim of the present study was to examinethe biomarkers of Pb, Hg, and Cd among Swedish adults. The die-tary associations, based on a 4-day food record and a food fre-quency questionnaire, as well as associations with other lifestylefactors for the metal concentrations in blood were also investi-gated. Measured levels of these metals were subsequently com-pared to internationally agreed reference health values.

2. Material and methods

2.1. Study design and population

The study was based on a subgroup of Riksmaten 2010–2011, a Swedish na-tional survey investigating dietary habits among adults (18–80 years) conductedbetween May 2010 and July 2011 (Amcoff et al., 2012). The subgroup consistedof participants who in addition to dietary registration and questionnaire also do-nated blood and urine samples. The sampling was performed at Occupational andEnvironmental Medicine Centers (OEMCs). Therefore Sweden was divided into se-ven regions according to affiliation to Swedens seven OEMCs (Fig. 1). Each regionincluded the region capital (Linköping, Lund, Stockholm, Umeå, Uppsala, Gothen-burg, Örebro) and two additional counties that were randomly selected. Data werecollected at four occasions; May/June 2010, August/September 2010, January/Feb-ruary 2011, and April/May 2011. Within each region, an equal number of individu-als were asked to participate independently of population size (12 individuals percounty and occasion). Of the 1008 randomly selected individuals, 300 (30%) choseto participate in the blood and urine sampling. Blood metal concentrations weremeasured in 297 participants. Of these, 22 individuals lacked food records and/orquestionnaire data and were excluded. Moreover, since the investigated metalsare excreted via urine and feces, two individuals with known kidney disease wereomitted. Thus, 273 participants with blood analyses were included in the presentstudy. Urine levels of Cd were measured in 289 individuals. Since urinary flowcan affect Cd concentrations, we corrected assessed urinary cadmium concentra-tions for creatinine levels. Also, we excluded individuals with creatinine concentra-tions 61 mmol/L (n = 3) since very dilute urine samples are considered not toprovide good estimates of the urinary excretion of biomarkers, even after adjust-ment (Aitio et al., 2007; Soharan et al., 2008). After further exclusion of those lack-ing food records or questionnaire and the two individuals with kidney disease, 262individuals were included in the statistical analyses with U-Cd levels. The sampleselection was performed by Statistics Sweden (SCB). The study was approved bythe regional ethical committee in Uppsala. All participants gave oral informed con-sent before entering the study.

2.2. Assessment of diet and lifestyle

In the national dietary survey Riksmaten 2010–2011, a representative sample of5000 individuals between 18–80 years and living in Sweden were invited to partic-ipate (Amcoff et al., 2012). The data collection took place between May 2010 andJuly 2011. The participants, all together 1797 women and men, reported everythingthey ate and drank during four consecutive days. The reporting was done in a web-based food diary. To cover all days of the week, starting day was randomly selected(Tuesday, Wednesday, Saturday or Sunday). A questionnaire with about 50 ques-tions was additionally used to collect data about less frequently consumed fooditems (e.g. consumption frequency of different classes of fishes and meat), educa-tion, smoking, and breast-feeding. Education was divided into elementary school,high-school, and higher education. Smoking status was classified according to neversmoker, former smoker, occasional smoker, and daily smoker. Self-reported weightand height were assessed and body mass index (BMI) was calculated (weight [kg]divided by height [m] squared). Associations between metal concentrations andthe following food groups were tested: dairy products, eggs, poultry, vegetables,fruits, potatoes, cereals, fish, meat, sausage, offal, alcohol, and discretionary food(defined as sweets, snacks, ice-cream, pastries, jam, and soft drinks).

2.3. Sampling of blood and urine

Non-fasting blood and single spot urine were sampled at the OEMC in each re-gion or by district health care centers. Blood was drawn from an antecubital vein.Plasma for the ferritin analyses was separated by centrifugation before storage.The samples were stored at �20 �C until analysis.

2.4. Chemical analyses

The concentrations of Cd in urine (U-Cd) corrected for molybdenum oxide inter-ference and Cd and Pb in whole blood (B-Pb) were determined by inductively cou-pled plasma mass spectrometry (ICP-MS; Thermo X7, Thermo Elemental, Winsford,UK) (Barany et al., 1997). The limits of detection (LOD) for U-Cd, B-Cd and B-Pb were0.02, 0.04 and 0.11 lg/L, respectively. Mercury in whole blood (B-Hg) was deter-mined in acid-digested samples by cold vapor atomic fluorescence spectrophotom-etry (Sandborgh-Englund et al., 1998). The detection limit was 0.09 lg/L. To ensurethe accuracy of the analytical methods and results, quality control (QC) sampleswere analysed along with the collected samples (Table 1). All analysed sampleswere prepared in duplicate and the method imprecisions (calculated as the coeffi-cients of variation in measurements of duplicate preparations) were 6.3%, 4.0%,1.6%, and 8.2%, for U-Cd, B-Cd, B-Pb and B-Hg, respectively. Plasma ferritin concen-tration was assessed by chemiluminescent microparticle immunoassay (ARCHI-TECT�, Abbott, US). Creatinine was measured in urine by an enzymatic method aspreviously described (Mazzachi et al., 2000).

2.5. Statistical analyses

The statistical analyses were carried out by STATA version 12 (StataCorp LP, US).Variables are presented as mean ± SD or median (percentiles 5–95th). Non-normalvariables were logarithmically transformed and if not attaining normality, non-parametric tests were used. The relationships between metal concentrations andexplanatory variables were examined by stepwise forward regression (significancelevel: p < 0.05). Comparisons between groups were performed by ANOVA or Krus-kal–Wallis test and adjusted for potential confounders by ANCOVA or residualmethod. Adjusted means were calculated by linear model. Correlations were inves-tigated by Pearson correlation and, for non-normal variables, Spearmans rank cor-relation. To avoid bias caused by outliers, the analyses were also performed afterexcluding outliers (3rd quartile + 1.5 � interquartile range). Limits and number ofoutliers were as follows; B-Pb: 32.33 lg/L (n = 6), B-Hg: 3.98 lg/L (n = 11), B-Cd:0.58 lg/L (n = 23), U-Cd: 0.57 lg/g creatinine (n = 17). P < 0.05 was considered sta-tistically significant.

3. Results

3.1. Population characteristics

Population characteristics and metal concentrations in wholeblood and urine by gender are presented in Table 2. None of theparticipants had B-Pb and B-Cd levels below the detection limit(<0.11 and <0.04 lg/L, respectively), four individuals had B-Hg 6 0.09 lg/L, and eight individuals had U-Cd 6 0.02 lg/L. Theseresults were included even if measured concentrations were belowthe detection limit. The median values (5–95th percentiles) of themetals in blood among all participants were as follows; B-Pb: 13(5.8–29) lg/L, B-Hg: 1.1 (0.31–3.5) lg/L, and B-Cd: 0.19 (0.09–1.1) lg/L. The median (5th–95th percentiles) of U-Cd was 0.16(0.04–0.63) lg/g creatinine. The distributions of the metal concen-trations are shown in Fig. 2. Among fertile women (18–45 years,n = 64), blood concentrations were as follows; B-Pb: 9.8 (4.7–18)lg/L, B-Hg: 0.70 (0.12–2.5) lg/L, and B-Cd: 0.19 (0.08–0.94) lg/L.Urinary Cd concentrations among fertile women (n = 60) were0.11 (0.04–0.34) lg/g creatinine.

3.2. Blood concentrations of lead

B-Pb levels were positively associated with age (mean% increaseper year [standard error, SE]: 1.0 [0.2]), male gender (mean% differ-ence [SE]: 22.5 [6.4]), and smoking (mean% change from non-smo-ker to daily smoker [SE]: 22.3 [10.7]), but not with education, BMI,reported energy intake or plasma ferritin in multivariable analysis.There were no statistically significant differences in B-Pb concen-trations between Swedish regions (i.e. areas of Linköping, Lund,Stockholm, Umeå, Uppsala, Gothenburg, Örebro; see map, Fig 1).

In stepwise regression analysis, B-Pb was associated with in-takes of alcohol and potatoes (mean% changes per g/d [SE]: 0.04[0.01] and 0.08 [0.03], respectively), but not vegetables, fruits,cereals, fish, meat, sausage, offal, or discretionary food. Alcoholbut not potatoes remained related after adjustments for age,

Fig. 1. Map over Sweden showing the seven OEMCs and their respective reception regions. (OEMCs = Occupational and Environmental Medicine Centers).

H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169 163

gender, education, smoking, and plasma ferritin (Fig. 3). Meat in-take assessed by food records was not related to B-Pb. However,when examining the impact of type of meat on B-Pb assessed by

food frequency questionnaire, frequency of game intake, but notreindeer, sheep, horse, bovine, pig, bird, or fish, was associatedwith B-Pb. This was valid also after adjusting for age, gender,

Table 1Results from analytical quality control (QC) of cadmium in urine (U-Cd), cadmium in blood (B-Cd), lead in blood (B-Pb) and total mercury in blood (B-Hg).

Quality control material Batch Analyte Reference value mean ± SD (lg/L) Obtained value mean ± SD (lg/L) n

Seronorma OK0436 U-Cd 0.26–0.36 0.28 ± 0.01 9QTCb D0514 U-Cd 1.01 ± 0.09 0.94 ± 0.03 9

D0905 U-Cd 5.1 ± 0.26 4.9 ± 0.09 9Seronorma 1003191 B-Cd 0.59–0.75 0.65 ± 0.07 11

1003191 B-Pb 14–16 16 ± 0.57 11QTCb C0616 B-Cd 1.1 ± 0.14 0.98 ± 0.06 11

L0909 B-Pb 23 ± 1.1 23 ± 1.1 11L0807 B-Pb 114 ± 9.1 116 ± 7.3 11

Seronorma 1003191 B-Hg 1.8–2.2 1.9 ± 0.10 310512627 B-Hg 16–20 15 ± 0.79 31

a SERO AB, Billingstad, Norway.b Centre de Toxicologie du Quebec International Comparison program, Quebec Canada.

Table 2Population characteristics and metal concentrations among women and men.

Women (n = 145) Men (n = 128) pa

Age (years) 48.2 ± 16.5 52.5 ± 17.0 0.03BMI (kg/m2) 24.1 (19.8–32.9) 25.2 (21.8–32.5) 0.10Education 0.44

Elementary school 18 (12%) 23 (18%)High-school 65 (45%) 53 (41%)Higher education 62 (43%) 52 (41%)

Smoking status 0.29Daily 13 (9%) 5 (4%)Occasional 10 (7%) 12 (9%)Ceased 41 (29%) 43 (34%)Never 78 (55%) 68 (53%)

B-Pb (lg/L) 12 (5.3–25) 15 (7.0–29) <0.001B-Hg (lg/L) 0.97 (0.17–2.9) 1.3 (0.39–4.4) <0.001B-Cd (lg/L) 0.22 (0.09–1.2) 0.17 (0.08–0.85) <0.001U-Cd (lg/g creatinine)b 0.20 (0.05–0.75) 0.12 (0.04–0.48) <0.001P-Ferritin (lg/L) 51 (8–186) 143 (36–449) <0.001

Age is presented as mean ± SD. The other numerical variables are presented asmedian (5–95th percentiles).

a p Denotes differences between genders.b n = 262 (137 women, 125 men).

164 H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169

education, smoking, and plasma ferritin (Fig. 3). B-Pb concentra-tions did not differ if the participants received their drinking waterfrom water well or municipal water supply system.

3.3. Blood concentrations of mercury

Higher age (mean% increase per year [SE]: 1.9 [0.3]), male gen-der (mean% difference [SE]: 34.1 [13.1]), and higher education(mean% change from lowest to highest education [SE]: 51.1[21.8]) were associated with higher B-Hg concentrations whereasthere was no relationship with BMI, energy intake, smoking orplasma ferritin in multivariable analysis. There were no statisti-cally significant differences between Swedish regions with regardto B-Hg concentrations.

Intakes of fish and vegetables assessed by food records werepositively related to B-Hg in stepwise regression (mean% changesper g/d [SE]: 0.88 [0.12] and 0.13 [0.04], respectively), whereasthere were no associations for potatoes, fruits, cereals, meat, sau-sage, offal, alcohol, and discretionary food. These associations re-mained after adjusting for age, gender, education, smoking andplasma ferritin. Fish intake assessed by food frequency question-naire was also associated with B-Hg (Fig. 3). Other types of meat(i.e. game, reindeer, sheep, horse, bovine, pig, and bird) were notrelated to B-Hg taking age, gender, education, smoking, and plasmaferritin into account, and excluding outliers. When associating B-Hg with type of fish assessed by food frequency questionnaire(i.e. shellfish, salt-water fish, and fresh-water fish), all three

categories were related. However, after adjusting for age, gender,education, smoking and plasma ferritin, the association withfresh-water fish was no longer significant whereas it remained sig-nificant for shellfish and salt-water fish. Drinking water from waterwell or municipal water supply system was not associated with B-Hg concentrations.

3.4. Blood and urine concentrations of cadmium

Cd levels in blood and urine (creatinine adjusted) were corre-lated (r = 0.65, p < 0.001) (Fig. 4). B-Cd concentrations were higheramong smokers (mean% change from non-smoker to daily smoker[SE]: 367 [49]), higher among women (mean% difference [SE]: 20.3[5.5]), positively associated with age (mean% increase per year[SE]: 1.3 [0.2]), and inversely related to plasma ferritin levels(mean% change [SE]: �0.10 [0.03]), whereas no relations were ob-served for education, BMI, or energy intake in multivariable analy-sis. When measured in urine, Cd was associated with smoking,gender, and age but not the other variables. No statistically signif-icant differences in blood or urinary Cd concentrations were ob-served between different Swedish regions.

Intakes of meat and discretionary food assessed by food recordswere negatively associated with B-Cd in stepwise regression(mean% changes per g/d [SE]: �0.34 [0.09] and �0.07 [0.02],respectively) (Fig. 3). The association with meat remained afteradjusting for age, gender, education, smoking, and plasma ferritin.Intake of sausage was additionally negatively associated with B-Cdin the analysis when outliers were excluded. The other food itemsincluded in the analysis (i.e. potatoes, vegetables, fruits, cereals,fish, offal, and alcohol) were not associated. Even though total meatintake was related to B-Cd, no association with type of meat as-sessed by food frequency questionnaire was observed. When mea-sured in urine, Cd concentrations were inversely related to intakesof meat, discretionary food, and cereals, and positively related tointake of fruits and berries. All associations but meat intake disap-peared after adjustments for age, gender, education, smoking, andplasma ferritin. Cd levels in blood or urine were not dependent onwhether the participants received their drinking water from waterwell or municipal water supply system.

Since smoking were strongly related to Cd levels, the associa-tions between Cd and personal characteristics, diet and other life-style factors were additionally investigated among never-smokersonly. In these analyses, the results were similar as in the primaryanalyses when smokers were included. However, among never-smokers only, high consumptions of pig and game assessed by foodfrequency questionnaire were associated with lower concentra-tions of B-Cd.

Fig. 2. Distribution of metal concentrations in the study population. Blood analyses: n = 273, urine analysis: n = 262.

H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169 165

3.5. Exclusion of outliers

To avoid extreme values from affecting the results, all analyseswere additionally performed after excluding outliers. This didhowever not appreciably change the results or the interpretation(data not shown).

4. Discussion

4.1. Lead

In this general Swedish adult population, Pb concentrations inblood were higher among men than women, a difference also ob-served by others (Barany et al., 2002; Clark et al., 2007; Nordberget al., 2000; Wennberg et al., 2006). This may partly be due to thatB-Pb mainly is present in erythrocytes and that men have a higherfraction of erythrocytes in whole blood than women (Skerfvinget al., 1999). Men are also more likely to have occupational expo-sure. The positive association between B-Pb levels and age amongadults observed here and by others (Clark et al., 2007) may be anage cohort effect, reflecting a higher exposure early in life amongthe older individuals, and that the higher blood levels partly arederived from endogenous storages (Skerfving et al., 1999). Forexample, the reduction of lead in gasoline has caused a majorexposure reduction also in B-Pb in Sweden (Stromberg et al.,2008). The higher B-Pb concentrations among smokers are inaccordance with other studies (Skerfving et al., 1999; Wennberget al., 2006).

In a Swedish food basket case study, fruit was estimated to con-tribute the most to the dietary exposure of Pb (21%), followed bypotatoes (14%), and sugar and sweets (14%) (NFA, 2012a). We did

observe an association with potatoes, which did not remain afteradjusting for potential confounders. Potato consumption has beenrelated to Pb levels in blood (Clark et al., 2007) and in breast milk(Garcia-Esquinas et al., 2011). Regarding the positive relationshipbetween B-Pb and alcohol consumption found in the present study,an association with wine has been reported previously (Wennberget al., 2006; Vahter et al., 1991). Even though total meat intake as-sessed by food records was not related to B-Pb, we observed higherlevels among those consuming more game according to the foodfrequency questionnaire. Interestingly, Pb from lead bullets usedin game hunting may be a source of Pb (Hunt et al., 2009) andthe Swedish National Food Agency has recently introduced adviceregarding Pb risks and consumption of game meat (NFA, 2012b).

4.2. Mercury

Since total-Hg was measured and no data on dental amalgamwere assessed, the contribution of inorganic Hg from amalgam(Bjornberg et al., 2005) to the observed circulating Hg levels is un-known. Most elderly people in Sweden have dental amalgam fill-ings, while today this is rare among those below 30 years of age.Usually 40–60% of Hg in blood is methyl mercury (Sandborgh-Englund et al., 1998; Vahter et al., 2000). Men had higher B-Hg lev-els than women. Also in a Canadian study, men had higher B-Hgthan women (Clark et al., 2007), even though the gender differ-ences do not seem as clear as for B-Pb and B-Cd (Skerfving et al.,1999). It is probable that fertile women consume less fresh-waterfish due to the recommendations to limit intake in this targetgroup and therefore lower blood levels are observed amongwomen. B-Hg increased with age in line with previous results(Wennberg et al., 2006). One explanation may be that elderly

Fig. 3. Blood metal concentrations (adjusteda means and 95% CI), dietary intake and smoking habits. (a) Blood concentrations were adjusted for age, gender, education,smoking, and plasma ferritin, but also intake of other food components as described in the result section, (b) alcohol, vegetable, and meat intakes were assessed by foodrecords and divided into tertiles (n = 268, alcohol; <25 g/d, <175 g/d, 61879 g/d, vegetables; <145.3 g/d, <214.6 g/d, 6731.2 g/d, meat; <43.9 g/d, <76, 5 g/d, 6256.0 g/d), (c)game and fish consumptions were assessed by food frequency questionnaire (game; n = 51 [never], n = 148 [<1/mo], n = 49 [P1/mo], and fish; n = 30 [61/mo], n = 156 [>1/mo], n = 62 [>1/wk]) and (d) smoking; n = 146 [never], n = 83 [ceased], n = 21 [occasional], n = 18 [daily].

Fig. 4. Relation between B-Cd and U-Cd from 262 matching blood-urine samplesobtained in the Riksmaten 2010–2011 study, showing a significant correlation(p < 0.001).

166 H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169

consume more fish, especially fresh-water fish (Johnsson et al.,2004; Amcoff et al., 2012). Moreover, lower exposure of inorganicHg is a result of decreased use of dental amalgam; already in 2003less than 2% of the new fillings were of amalgam type (Swedish Na-tional Board of Health and Welfare).

Fish is the main contributor to Hg exposure in Sweden (NFA,2012a) and consumption has been associated with B-Hg (Johnssonet al., 2005; Bjornberg et al., 2005; Wennberg et al., 2006). There-fore the observed relation between fish intake and B-Hg was ex-pected. However, when dividing the fish consumption intocategories, rather surprisingly, fresh-water fish did not remainassociated after adjustments for confounders. Possibly theconsumption was too low in relation to other fish groups includingsalmon and lean seawater fish. Moreover, adherence to the dietaryrecommendations issued by the Swedish National Food Agencymay have reduced the intake of fish containing high amounts ofHg. The observed positive association between B-Hg levels and in-take of vegetables may be due to that individuals consuming highamounts of fish adhere to an overall healthy diet and thus alsohave a higher intake of vegetables (the correlation between intakesof fish and vegetables was significant [r = 0.18, p = 0.002]).

H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169 167

4.3. Cadmium

Cd levels increased with age, which is primarily an effect of thevery long half time (Nordberg et al., 2007; Olsson et al., 2002;Wennberg et al., 2006). As expected (Berglund et al., 1994; Ander-sen et al., 2004; Barany et al., 2005; Olsson et al., 2002; Wennberget al., 2006), plasma ferritin levels were inversely related with B-Cd. This is probably due to up-regulation of transporters causedby low iron stores influencing Cd absorption (Vahter et al., 2007).Lower iron stores among women than men therefore provide aprobable explanation for the observed higher B-Cd levels in wo-men in the present study and elsewhere (Olsson et al., 2002;Wennberg et al., 2006). Lower iron status due to less meat intakemay also explain the negative correlation between meat intakeand B-Cd.

No strong dietary factors were observed with regard to Cd inblood or urine. It is possible that the dietary habits within the pop-ulation were too homogenous to detect any differences, or that theintake of key food items, such as cereals (NFA, 2012a), was difficultto estimate since it is present in a diversity of food products andtherefore also complicated to assess accurately. Cereals, bread,potatoes, and vegetables have been described as the major dietaryCd sources (NFA, 2012a; Olsson et al., 2002). None of these associ-ations were observed in the present study. However, higher B-Cdwas observed among those consuming less discretionary food. Itis possible that individuals consuming less discretionary food havea healthier lifestyle and thus a higher fiber intake. In anotherobservational study, a high fiber intake was associated with a high-er Cd exposure (Berglund et al., 1994). However, fiber intake hasalso been associated with lower B-Cd among smoking but notnon-smoking men (Kim et al., 2010) and diets high in refined car-bohydrates and low in fiber seem to increase the intestinal Cd up-take in animals (Andersen et al., 2004). Intake of meat wasinversely related to B-Cd. Meat has previously been estimated tocontribute to the dietary Cd burden with only approximately 4%(NFA, 2012a). Therefore, as discussed above, iron may explain theobserved association. For U-Cd, an inverse association with meatintake could be caused by increased excretion of creatinine, usedto adjust U-Cd levels. Smoking is a major source for Cd exposure(Ferraro et al., 2010; Wennberg et al., 2006), something we also ob-served in the present study.

4.4. Geographic differences within Sweden

The classification of Sweden into seven regions in the presentstudy may have been too broad to observe any geographical differ-ences in metal concentrations. Instead smaller regions defined byCd-soil content, as used elsewhere (Olsson et al., 2002), may benecessary to detect any geographic differences. On the other hand,a centralized food market may obstruct any potential geographiceffects. Contribution of Cd from locally produced food has beenestimated to 17% of total Cd intake in a Swedish study (Olssonet al., 2002). Even though there was a wide range of this contribu-tion to body Cd levels, the impact for most individuals seemedlimited.

4.5. Comparison with other populations and risk estimations

The blood concentrations of Cd, Pb, and Hg are in accordancewith Swedish data (Barany et al., 2002; Gerhardsson and Lundh,2010; Olsson et al., 2002) as well as data from other countries(Table 3). However, the considerably high levels of metals in someregions suggest problems that may be related to specific exposureconditions. Among fertile women in the present study, 30% had B-Pb levels above the reference point of 12 lg/L for developmentalneurotoxicity established by EFSA (EFSA, 2010). This reference

point equals the lower confidence limit on a benchmark dosecorresponding to an extra risk of 1% (BMDL01), which implies a de-crease in one IQ point. In the entire study population, most individ-uals were below the reference point (BMDL01) for potential effectson blood pressure set at 36 lg/L, but a large part of the studypopulation seemed to be above the reference point (BMDL10) forpossible nephrotoxic effects at 15 lg/L. With regard to B-Hg, con-centrations below 4.8 and 8.8 lg/L are judged by the American Na-tional Research Council and the Joint FAO/WHO Expert Committeeon Food Additives and Contaminants, respectively, having no riskof fetal neurotoxic damages (NRC, 2000; WHO, 2004; NFA, 2007).The highest concentration among fertile women in the presentstudy was 3.8 lg/L and thus below the mentioned reference points.Regarding U-Cd, the critical concentration of 1 lg/g creatinine setby EFSA (EFSA, 2009) relates to a level below which no increasedrisk for renal adverse effects should be expected. In our study,the 95th percentile for U-Cd was 0.6 lg/g creatinine and thus thereseems to be a margin to the critical U-Cd concentration for the gen-eral adult Swedish population. However, four individuals (age 40–70 years) had U-Cd above 1 lg/g creatinine (maximum level was3.7 lg/g creatinine) and may have increased risk for adverse effectson kidney and/or bone.

4.6. Strengths and limitations

Strengths of this study are the nation-wide perspective includ-ing both gender, a broad age span of the Swedish adult population(18–80 years), and several geographic regions. The study suffersfrom a low participation rate (30%), but there were no statisticalsignificant differences between participants and 377 non-partici-pants for which register data was obtained with regard to age, gen-der, income, or geography, whereas education was higher amongparticipants (data not shown). Another strength with the study isthe use of both 4-days food records and food frequency question-naire. Thus, a better characterisation of the participants dietaryhabits is probably achieved than when using only one method.Moreover, Cd levels were measured in both blood and urine,strengthening the results. One limitation is that exposure of themetals and dietary habits earlier in life may have affected theresults. Also, the assessment of dietary habits and metal concentra-tions in blood and urine were not performed at the same time. Inaverage blood sampling was performed 15 days after the start offood recording (p5–p95: 2–57 days). However, the registered dietis believed to sufficiently reflect habitual intake. Furthermore, anadvantage is the precise and accurate analytical methods usedwith extensive use of reference materials and participation in in-ter-laboratory control programs.

5. Conclusions

In this Swedish study, a nation-wide approach was used to sur-vey dietary habits, lifestyle factors and metal concentrations inblood and urine. Among adults of 18–80 years of age, blood con-centrations of Pb, Hg, and Cd were associated with age, genderand dietary factors. The major contributor to Hg exposure seemedto be fish whereas intakes of game and alcohol were related tohigher Pb levels. Important factors for Cd levels in blood appearedto be smoking and iron deficiency. In case of Hg and Cd, measuredblood and urinary levels were, with some minor exceptions, belowhealth based reference points. For Pb, on the other hand, a largepart of the study population seemed to be above the referencepoint for possible nephrotoxic effects, and 30% of fertile womenhad levels above the reference point for developmental neurotox-icity established by EFSA (2010). Thus, as health effects cannotbe excluded, individuals with high Pb exposure should aim at

Table 3Mean levels of lead, mercury and cadmium in whole blood samples from various populations, in comparison to the present study (geom. means, in lg/L).

Country, region Population Pb Hg Cd References

Sweden, present study Adults 18–74 yr, pop. based study 13.4 1.08 0.22Germany, north Adult volunteers, n = 130 19 0.9 0.38 Heitland and Köster (2006)Czech Republic Adults, 18–58 yr 65a 2.8a 1.0a Cerna et al. (2012)Canada Country representative, 6–79 yr, n = 2576–2743 13.4 0.69 0.35 Haines and Murray (2012)Canada, west coast Non-smoking, oyster-growers, 30–65 yr, n = 61 21 2.9 n.d. Clark et al. (2007)USA, NHANES 2007–2008 Adults (n = 4409) 14.3 0.96 0.38 Chen et al. (2013)Korea, South Adults (>20 yr, n = 5924) 22.9 0.97 4.30 Kim and Lee (2012)

n.d. = Not determined.a ‘‘Reference value’’ 2005–2009.

168 H. Bjermo et al. / Food and Chemical Toxicology 57 (2013) 161–169

decreasing their body burden, both from food and from other expo-sure routes.

Funding

This study was funded by the Swedish Environmental Protec-tion Agency.

Ethics

The study was approved by the regional ethical committee inUppsala, Sweden.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgments

The authors thank the staff at the Occupational and Environ-mental Medicine Centres for the collection of the samples, andIngalill Gadhasson at the National Food Agency for preparationand organization during sampling collection. Peter Ridefeldt,Akademiska Hospital, Uppsala, is acknowledged for contributingwith expert skills in biomonitoring. Anna Akantis, Berit Holmskovand Giovanni Ferrari are acknowledged for skilful technical assis-tance with metal analyses. Merethe Andersen is acknowledgedfor graphical work. The Swedish Environmental Protection Agencyis acknowledged for funding.

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