Int. J. Epidemiol.-2012-Ford-1338-53

8/12/2019 Int. J. Epidemiol.-2012-Ford-1338-53

1/16

Sedentary behaviour and cardiovasculardisease: a review of prospective studiesEarl S Ford* and Carl J Caspersen

Division of Population Health and the Division of Diabetes Translation, National Center for Chronic Disease Prevention and HealthPromotion, Centers for Disease Control and Prevention, Atlanta, GA, USA

*Corresponding author. Centers for Disease Control and Prevention, 4770 Buford Highway, MS K67, Atlanta, GA 30341, USA.Email: [email protected]

Accepted 16 April 2012

Background Current estimates from objective accelerometer data suggest that American adults are sedentary for 7.7 h/day. Historically, seden-tary behaviour was conceptualized as one end of the physicalactivity spectrum but is increasingly being viewed as a behaviourdistinct from physical activity.

Methods Prospective studies examining the associations between screen time(watching television, watching videos and using a computer) andsitting time and fatal and non-fatal cardiovascular disease (CVD) were identified. These prospective studies relied on self-reportedsedentary behaviour.

Results The majority of prospective studies of screen time and sitting timehas shown that greater sedentary time is associated with anincreased risk of fatal and non-fatal CVD. Compared with thelowest levels of sedentary time, risk estimates ranged up to 1.68for the highest level of sitting time and 2.25 for the highest level of screen time after adjustment for a series of covariates, includingmeasures of physical activity. For six studies of screen time andCVD, the summary hazard ratio per 2-h increase was 1.17 (95%CI: 1.131.20). For two studies of sitting time, the summaryhazard ratio per 2-h increase was 1.05 (95% CI: 1.011.09).

Conclusions Future prospective studies using more objective measures of seden-tary behaviour might prove helpful in quantifying better the riskbetween sedentary behaviour and CVD morbidity and mortality.This budding science may better shape future guideline develop-ment as well as clinical and public health interventions to reducethe amount of sedentary behaviour in modern societies.

Keywords Cardiovascular diseases, prospective studies, sedentary lifestyle,

television

IntroductionThe first Surgeon Generals Report on Physical Activity and Health in 1996 summarized almost fourdecades of epidemiolo gical research on various healthand disease outcomes. 1 This report marked a criticaldevelopmental milestone in raising the consciousness

about the importance of physical activity in enhancingthe health of Americans for both the public healthcommunity and general public and drew attentionto the enormous public health burden of being theleast active group in a population.

Technological innovations displaced manylabour-intensive physical activities at work, in the

Published by Oxford University Press on behalf of the International Epidemiological Association 2012. Advance Access publication 26 May 2012

International Journal of Epidemiology 2012;41 :13381353doi:10.1093/ije/dys078

1338


2/16

home and for transportation. A recent review of USstudies estimated that mean occupational energyexpenditure may have decreased by 14 2 calories/dayfrom 196062 to 200306 among men. 2 New inven-tions, such as television and computers, led to a newparadigm of recreation that increasingly becamesedentary during leisure time. The increasing popular-ity of the automobile ushered in an era of decliningnon-motorized transportation.

Historically, physical activity epidemiologicalresearch sought to unravel relation ships betweenenergy expenditure and health benefits. 3 The resultingphysical activity guidelines predicated on this research were largely oriented towards increasing physicalactivity levels in the populat ion rather than reducingsedentary behaviour, per se. 1 Most early researchersregarded time spent in sedentary behaviours during work, leisure and transportation as part of one endof a physical activity spectrum. An emerging concep-tualization views sedentary behaviours as somewhatdistinct from physical activity ( Figure 1 ) and recog-nizes that, paradoxically, high levels of sedentarybehaviour can coexist with high levels of totalphysical activity. 4

In this review, our primary objective was to examinethe relationship between sedentary behaviour andcardiovascular morbidity and mortality using pro-spective observational studies conducted largelyduring the past decade. Our secondary objectives were to summarize the evolution of epidemiologicalthought concerning possible adverse health effects of sedentary behaviour, present emerging evidence sup-porting links between sedentary behaviour and

cardiovascular disease (CVD), illustrate the highprevalence of sedentary behaviour and review the lim-ited evidence concerning mechanisms specific tosedentary behaviour underlying a possible association with CVD.

Defining sedentary behaviour Activities having a metabolic expenditure rangingfrom 4 1.0 MET (one MET is resting energy expend-iture set at 3.5 ml of oxygen/kg body m ass/min) to

1.5 METs are considered sedentary, 5 althoughsome rese archers suggest the range should extend to2.0 METs.6 Alternatively, because the MET value of quietly standing can be as little as 1.2, some haveproposed that sedentary behav iour should be re-stricted to non-upright activities. 7 Hence, definitionaldifferences abound.

Generally, sleeping has a MET level of 0.9 MET.8

Other sedentary activities include sitting, reading,meditating, relaxing, thinking, receiving a massage,

watching television, using a computer, listening tomusic or the radio, talking on the telephone, writingletters, playing cards and riding in a car. Most of these activities involve basically sitting. However,tabled MET values for different types of sittingrange from 1.0 to 4 2.0. Although not synonymous,sedentary behaviour and sitting clearly overlap.

Sedentary behaviours exist in many contexts: occu-pation, household, leisure-time and transportation.

Measuring sedentary behaviourResearchers have used at least four methods to assesssedentary behaviour. Firstly, in occupational studies,those using job ratings developed by experts havecrudely categorized workers into some framework.

Secondly, researchers have estimated sedentarybehaviour from generally brief questionnaires. Thismethod predominates in more recent prospective stu-dies of the relationship between sedentary behaviourand adverse health events.

Thirdly, heart rate monitors can be used to assesssedentary behaviour. 9 , 10

Finally, accelerometers that can objectively assesssedentary behaviour have advanced greatly withimproved utility and falling unit costs. They havebecome increasingly attractive for large population-based studies, such as recent cycles of the National

Health and Nutrition Examination Survey (NHANES)of the US population. 1113

Prevalence of sedentary behaviour Adults in many Western countries spend large partsof their days being sedentaryup to half of a day foremployed persons. 14 Nielsen Inc. reported that theaverage American in 2010 spent 35 h/week watchingTV, 2 h watching time-shifted TV, 20 min watchingonline videos, 4 min watching mobile video and 4hon the internet. 15 Hence, time spent on screen

Sedentary behaviour

Moderate

Vigorous

Cardiovascularoutcomes

Confounders

Sedentary behaviourCardiovascular

outcomes

Confoundersincluding

physical activity

A

B

Figure 1 Traditional (A) and emerging (B) conceptualiza-tions of the relationships between sedentary behaviour andphysical activity and cardiovascular outcomes

SEDENTARY BEHAVIOUR AND CARDIOVASCULAR DISEASE 1339


3/16

viewing w as the most common sedentary leisure-timebehaviour. 3 ,16 Data from the National Human ActivityPattern Survey showed that the most common seden-tary activities, when ranked by the percentage of waking hours, were driving a car (10.9%), office work (9.2%), watching television or a movie (8.6%),performing various activities while sitting quietly(5.8%), eating (5.3%) and talking to someone inperson or over the phone (3.8%). 17 When asked,How much time do you usually spend sitting orreclining on a typical day?, US adults reported onaverage 5.5 h/day during 200708, with nearlyequal amounts for men and women, greater amountsfor Whites than for African Americans and Mexican Americans and increasing amounts with increasingage (Ford ES, personal observations from NHANES)(Figure 2 ). In contrast, accelerometer measurementsrevealed average sedentary time to be 7.7h/day, al so with little difference between men and women. 13

Australian adults showed that participants were sed-entar y f or 57% of the time that an accelerometer was worn. 18 If sleeping time is included as sedentary time,peop le may average 75% of the day being seden-tary. 7 Regarding transportation, the average on e- waycommuting time in USA in 2009 was 25.1min. 19

MethodsTo identify prospective studies of sedentary behaviourand cardiovascular incidence and mortality, we exe-cuted a search strategy using the PubMed database(Supplementary data are available at IJE online). After reviewing 1304 citations produced by that

search, we reviewed 37 articles in depth. In addition, we examined the bibliographies of articles that wereviewed. Studies had to be prospective, have

incidence or mortality from CVD as an outcome, spe-cifically assess sedentary behaviour (screen time andsitting) and be conducted on adults. We limited oursearch to publications written in English and did notcontact authors for additional information. At theconclusion of this process, we were left with ninestudies. Both authors abstracted the following dataelements: author, year of publication, exposure cate-gories, hazard ratios, 95% confidence intervals (CIs),adjustment variables, cardiovascular outcome,number of cardiovascular events and number of participants. Meta-analyses of the doseresponserelationships for screen time or sitting time wereperformed. For screen time, we used the estimatesof relative risk pe r 2 h of screen time that were previously calculated. 20 For newer studies of screen timeand studies of sitting time, we calculated estimatedrelative risks per 2 h/day of sc reen time from cate-gories of sedentary behaviour. 21 For each study, astandard error was derived from the CI and a weight was calculated as the inverse of the variance(1/SE 2 ). Hetero geneity was assessed with the Q stat-istic and I .22 , 23 Depending on these statistics, fixedeffect or random effect estimated relative risks werecalculated. Stata 10 was used to conduct the analyses.

Prospective studiesOccupational studies A seminal study by Morris et al.24 was conductedusing about 31 000 employees aged 3564 years of the London Transport Executive, who were followedduring 194950. When compared with conductors,bus drivers had about double the age-adjusted rateof fatal coronary heart disease (CHD), but a similarrate of non-fatal CHD. This was the first indicationthat sedentary behaviour could markedly increase

0 50 100 150 200 250 300 350 400

Age 60 yearsAge 4059 yearsAge 2039 years

Mexican American

African AmericanWhite

Women

MenTotal

Minutes per day

Figure 2 Age-adjusted and unadjusted mean time (95% CI) spent in sedentary behaviour per day among adults aged20 years or older, NHANES 200708. The following question was asked about sitting or reclining work, at home or atschool: Include time spent sitting at a desk, sitting with friends, travelling in a car, bus or train, reading, playing cards, watching television or using a computer. Do not include time spent sleeping. How much time do you/usually spend sittingor reclining on a typical day?

1340 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
http://ije.oxfordjournals.org/cgi/content/full/dys078/DC1http://ije.oxfordjournals.org/cgi/content/full/dys078/DC1http://ije.oxfordjournals.org/cgi/content/full/dys078/DC1


4/16

CHD risk. The authors also presented data on a largersecond cohort of male civil servants and post officeemployees aged 3559 years, followed during 194950(179726 person-years of follow-up). Based on job-related physical activity, participants weregrouped into three categories: sedentary, intermediateand relatively much physical activity. The correspond-ing age-adjusted rates (per 1000 person-years) of fataland non-fatal CHD were 2.4, 2.0 and 1.8, respectively.

Subsequent prospective studies used various meth-ods to examine whether drivers in the transp ortat ionindustry had an increased risk for CVD. 2533 A Swedish study found a 3-fold greater risk for fataland non-fatal CHD among urban bus and tram drivers compared with members of other occupatio nsafter adjustment for a wide variety of confounders. 33

Interestingly, lorry drivers were not at increased risk,a finding that the authors attributed to less job stressand air pollution exposure than that experienced byurban drivers. This study suggests caution in inter-preting transportation studies.

Other prospective occupational studies examined thelinks between occupational sitting or sedentarinessand CVD. A review of six such studies, each usingquestionnaires to assess sedentariness, failed toreach a definitive conclusion about the effect of occu-pational sedentary behaviour on CVD. 14 Four studiesshowed increased estimated relative risks for the mostsedentary compared with the most active group, 3437

where as in two studies, the 95% CI includedunity. 38 , 39 Only three reviewed s tudie s adjusted fornon-occupational physical activity. 3537

Although not entirely consistent, occupational stu-dies suggested that high levels of sedentary behaviourat work may increase the risk of developing CVD.Study limitations abounded, including a lack of CVDrisk factor data for statistical adjustment, a lack of follow-up of employees who left their jobs and limitedgeneralizability of findings. Also, in many occupa-tional studies, the healthy worker effect must beconsidere deven when internal comparisons areanalysed. 40 These studies did not examine the separ-ate contributions of sedentary behaviour and physicalactivity to CVD outcomes.

Population-based cohort studiesSitting. Several prospective studies examined thelinks between time spent sitting and CVD ( Table 1 ).In the Womens Health Initiative, 73 743 postmeno-pausal women aged 5079 years were followed for anaverage of 5.9 years duri ng which time 1551 cardiovascular events occurred. 41 A questionnaire assesseddaily time spent sitting. Compared with women whosat


5/16 T a b l e 1 S u m m a r y o f f i n d i n g s f r o m p r o s p e c t i v e s t u d i e s e x a m i n i n g l i n k s b e t w e e n s e d e n t a r y b e h a v i o u r a n d c a r d i o v a s c u l a r o u t c o m e s

R e f e r e n c e

S a m p l e s i z e ,

g e n d e r a n d a g e

N o . o f

e v e n t s

E x c l u s i o n s

F o l l o w - u p

( y e a r s )

S e d e n t a r y

c a t e g o r i e s

H a z a r d r a t i o

( 9 5 % C I )

A d j u s t m e n t f a c t o r s

M e a s u r e m e n t o f

p h y s i c a l a c t i v i t y

S i t t i n g

M a n s o n

e t a

l .

2 0 0 2 4 1

7 3 7 4 3 p o s t m e n o -

p a u s a l w o m e n ,

5 0 7

9 y e a r s

1 5 5 1 t o t a l

C V e v e n t s ,

3 4 5 i n c i -

d e n t C H D

P r e d i c t e d s u r v i v a l

< 3 y e a r s ; a l c o h o l i s m ;

m e n t a l i l l n e s s ;

d e m e n t i a ; h i s t o r y o f

C H D

, s t r o k e

, c a n c e r ;

n o n - a m b u l a t o r y

5 . 9

5 1 6 v s < 4 h / d a y 1 . 6 8 ( 1

. 0 7 2 . 6 4 )

A g e ,

e n e r g y

e x p e n d i t u r e

W e e k l y

M E T s c o r e d e r i v e d

f r o m

d e t a i l e d q u e s t i o n -

n a i r e o f m i l d

, m o d e r a t e o r

v i g o r o u s r e c r e a t i o n a l

p h y s i c a l a c t i v i t i e s

K a t z m a r z y k

e t a

l .

2 0 0 9 4 2

1 7 0 1 3 m e n

a n d w o m e n ,

1 8 9

0 y e a r s

7 5 9 C V D

d e a t h s

N o n e s t a t e d

1 2 . 0

A l m o s t n o n e o f

t h e t i m e

1 . 0 0

A g e ,

s m o k i n g , a l c o h o l u s e ,

l e i s u r e - t i m e p h y s i c a l a c t i v i t y

,

P h y s i c a l A c t i v i t y R e a d i n e s s

Q u e s t i o n n a i r e

A v e r a g e w e e k l y M E T - h o u r s

d u r i n g 1 2 - m o n t h p e r i o d

1 / 4 o f t h e t i m e 1 . 0 1 ( 0

. 7 7 1 . 3 1 )

1 / 2 o f t h e t i m e 1 . 2 2 ( 0

. 9 4 1 . 6 0 )

3 / 4 o f t h e t i m e 1 . 4 7 ( 1

. 0 9 1 . 9 6 )

A l m o s t a l l t h e

t i m e

1 . 5 4 ( 1

. 0 9 2 . 1 7 )

P a t e l e t a

l .

2 0 1 0 4 3

6 9 7 7 6 w o m e n ,

5 0 7

4 y e a r s

2 3 6 0 C V D

d e a t h s

H i s t o r y o f c a n c e r ,

h e a r t a t t a c k ,

e m p h y s e m a / o t h e r l u n g

d i s e a s e ; n o d a i l y l i f e

a c t i v i t i e s ; n o l i g h t

h o u s e k e e p i n g ; d e a t h s

w i t h i n f i r s t y e a r

1 4

< 3 h / d a y

1 . 0 0

A g e ,

r a c e ,

m a r i t a l s t a t u s ,

e d u -

c a t i o n , s m o k i n g s t a t u s ,

b o d y

m a s s i n d e x , a l c o h o l u s e ,

e n e r g y i n t a k e

, c o m o r b i d i t i e s

s c o r e , t o t a l p h y s i c a l a c t i v i t y

A v e r a g e M E T - h o u r s p e r

w e e k

d u r i n g p a s t y e a r f o r

r e c r e a t i o n a l a n d d a i l y l i f e

a c t i v i t i e s

3 5 h / d a y

1 . 2 0 ( 1

. 1 0 1 . 3 2 )

5 6 h / d a y

1 . 3 3 ( 1

. 1 7 1 . 5 2 )

5 3 4 4 0 m e n ,

5 0 7

4 y e a r s

4 0 0 9 C V D

d e a t h s

< 3 h / d a y

1 . 0 0

3 5 h / d a y

1 . 0 6 ( 0

. 9 9 1 . 1 4 )

5 6 h / d a y

1 . 1 8 ( 1

. 0 8 1 . 3 0 )

M a t t h e w s

e t a

l .

2 0 1 2

4 4

2 4 0 8 1 9 m e n

a n d w o m e n ,

5 0 7

1 y e a r s

4 6 8 4 C V

d e a t h s


C V D

, r e s p i r a t o r y

d i s e a s e

8 . 5

< 3 h / d a y

1 . 0 0

A g e ,

g e n d e r ,

r a c e ,

e d u c a t i o n ,

s m o k i n g h i s t o r y , d i e t q u a l i t y

,

m o d e r a t e v i g o r o u s p h y s i c a l

a c t i v i t y

A v e r a g e t i m e s p e n t e a c h

w e e k

i n a c t i v i t i e s o f

a t l e a s t a m o d e r a t e

i n t e n s i t y i n t h e p a s t

1 0 y e a r s

3 4 h / d a y

0 . 9 8 ( 0

. 9 0 1 . 0 6 )

5 6 h / d a y

1 . 0 2 ( 0

. 9 4 1 . 1 1 )

7 8 h / d a y

0 . 9 5 ( 0

. 8 6 1 . 0 6 )

5 9 h / d a y

1 . 1 6 ( 1

. 0 2 1 . 3 0 )

( c o n t i n u e d )



6/16 T a b l e 1 C o n t i n u e d

R e f e r e n c e



N o . o f

e v e n t s

E x c l u s i o n s

F o l l o w - u p

( y e a r s )

S e d e n t a r y

c a t e g o r i e s


( 9 5 % C I )




T e l e v i s i o n v i e w i n g

W a r r e n

e t a

l .

2 0 1 0 4 5

7 7 4 4 m e n ,

4 7 . 1

y e a r s

3 7 7 C V

d e a t h s

H i s t o r y o f M I ,

s t r o k e

, c a n c e r

2 1

Q 1

1 . 0 0

A g e ,



,



L e i s u r e

a n d w o r k p h y s i c a l

a c t i v i t y r a t e d r e l a t i v e

t o o t h e r s . W a s

d i c h o t o m i z e d i n t o

p h y s i c a l l y a c t i v e v s

i n a c t i v e

Q 2

1 . 0 2 ( 0

. 7 4 1 . 4 2 )

Q 3

1 . 2 7 ( 0

. 9 0 1 . 7 8 )

Q 4

0 . 9 6 ( 0

. 6 8 1 . 3 6 )

D u n s t a n

e t a

l .

2 0 1 0

4 6

8 8 0 0 m e n a n d

w o m e n ,

5 2 5 y e a r s

8 7 C V D

d e a t h s

H i s t o r y o f C V D

,

p r e g n a n c y , f a s t e d

5 9 h , o v e r - o r u n d e r -

r e p o r t e d e n e r g y i n t a k e

6 . 6

< 2 h / d a y

1 . 0 0

A g e ,

g e n d e r ,

s m o k i n g s t a t u s ,

e d u c a t i o n , e n e r g y i n t a k e

,

a l c o h o l u s e , D i e t Q u a l i t y

I n d e x , w a i s t c i r c u m f e r e n c e ,

h y p e r t e n s i o n ,

t o t a l

c h o l e s t e r o l , h i g h - d e n s i t y

l i p o p r o t e i n c h o l e s t e r o l ,

t r i g l y c e r i d e s , l i p i d - l o w e r i n g

m e d i c a t i o n s ,

o r a l g l u c o s e

t o l e r a n c e t e s t , l

e i s u r e e x e r c i s e

t i m e

A c t i v e A u s t r a l i a

q u e s t i o n n a i r e

2 < 4 h / d a y

1 . 1 9 ( 0

. 7 2 1 . 9 9 )

5 4 h / d a y

1 . 8 0 ( 1

. 0 0 3 . 2 5 )

W i j n d a e l e

e t a

l .

2 0 1 1

1 6

1 3 1 9 7 m e n a n d

w o m e n w i t h

m e a n 6 1

. 5 y e a r s 3

7 3 C V D

d e a t h s


s t r o k e

, c a n c e r

9 . 5

P e r h o u r / d a y

1 . 0 8 ( 1

. 0 1 1 . 1 6 )

A g e ,

g e n d e r ,

e d u c a t i o n , s m o k -

i n g s t a t u s ,

a l c o h o l u s e ,

m e d i c a t i o n s f o r h y p e r t e n s i o n

a n d d y s l i p i d e m i a

, h i s t o r y o f

d i a b e t e s ,

f a m i l y h i s t o r y o f

C V D a n d c a n c e r ,

p h y s i c a l

a c t i v i t y

E P A Q 2

P e r h o u r / d a y

1 . 0 7 ( 0

. 9 9 1 . 1 5 )

A g e ,

g e n d e r ,

e d u c a t i o n , s m o k -

i n g s t a t u s ,

a l c o h o l u s e ,

m e d i c a t i o n s f o r h y p e r t e n s i o n

a n d d y s l i p i d e m i a

, h i s t o r y o f

d i a b e t e s ,

f a m i l y h i s t o r y o f

C V D a n d c a n c e r ,

p h y s i c a l

a c t i v i t y

, w a i s t c i r c u m f e r e n c e

S t a m a t a k i s

e t a

l .

2 0 1 1 4 7

4 5 1 2 m e n a n d

w o m e n ,

5 3 5

y e a r s

2 1 5 C V

e v e n t s

P r e v i o u s h o s p i t a l

s t a y s f o r C V D

4 . 3

< 2 h / d a y

1 . 0 0

A g e ,

g e n d e r ,

e t h n i c i t y

, b o d y

m a s s i n d e x , s m o k i n g , s o c i a l

c l a s s , l o n g - s t a n d i n g i l l n e s s ,

m a r i t a l s t a t u s ,

d i a b e t e s ,

h y p e r t e n s i o n a n d p h y s i c a l

a c t i v i t y

A v e r a g e d a i l y t i m e o f

n o n - o c c u p a t i o n a l m o d e r -

a t e v i g o r o u s p h y s i c a l a c -

t i v i t y d u r i n g p a s t 4 w e e k s

.

O c c u p a t i o n a l p h y s i c a l a c -

t i v i t y i n 3 c a t e g o r i e s

2 < 4 h / d a y

2 . 2 3 ( 1

. 3 1 3 . 8 0 )



7/16 T a b l e 1 C o n t i n u e d

R e f e r e n c e



N o . o f

e v e n t s

E x c l u s i o n s

F o l l o w - u p

( y e a r s )

S e d e n t a r y

c a t e g o r i e s


( 9 5 % C I )




5 4 h / d a y

2 . 2 5 ( 1

. 3 0 3 . 8 9 )

M a t t h e w s

e t a

l .

2 0 1 2

4 4

2 4 0 8 1 9 m e n a n d

w o m e n ,

5 0 7

1

y e a r s

4 6 8 4 C V

d e a t h s


C V D

, r e s p i r a t o r y

d i s e a s e

8 . 5

< 1 h / d a y

1 . 0 0

A g e ,

g e n d e r ,

r a c e ,

e d u c a t i o n ,

s m o k i n g h i s t o r y , d i e t q u a l i t y

,

m o d e r a t e v i g o r o u s p h y s i c a l

a c t i v i t y

A v e r a g e t i m e s p e n t e a c h

w e e k

i n a c t i v i t i e s o f a t

l e a s t

a m o d e r a t e i n t e n s i t y

i n t h e p a s t 1 0 y e a r s

1 2 h / d a y

1 . 0 0 ( 0

. 8 6 1 . 1 6 )

3 4 h / d a y

1 . 1 5 ( 1

. 0 0 1 . 3 3 )

5 6 h / d a y

1 . 3 6 ( 1

. 1 7 1 . 5 9 )

5 7 h / d a y

1 . 8 5 ( 1

. 5 6 2 . 2 0 )

F o r d 2 0 1 2

4 8

7 3 5 0 m e n a n d

w o m e n ,

5 2 0 y e a r s

1 9 0 c i r c u l a -

t o r y

d i s e a s e

N o n e s t a t e d

5 . 8

< 1 h / d a y

1 . 0 0

A g e ,

g e n d e r ,

r a c e o r e t h n i -

c i t y ,

e d u c a t i o n , l e i s u r e - t i m e


, H e a l t h y

E a t i n g I n d e x s c o r e , a l c o h o l

c o n s u m p t i o n , h e a l t h s t a t u s

a n d h e a l t h i n s u r a n c e

c o v e r a g e

A v e r a g e w e e k l y m i n u t e s o f

m o d e r a t e a n d v i g o r o u s

l e i s u r e - t

i m e p h y s i c a l a c -

t i v i t y d u r i n g p a s t 3 0 d a y s

1 h / d a y

1 . 4 2 ( 0

. 6 4 3 . 1 7 )

2 h / d a y

0 . 8 2 ( 0

. 4 2 1 . 5 9 )

3 h / d a y

1 . 4 2 ( 0

. 6 1 3 . 3 0 )

4 h / d a y

0 . 8 4 ( 0

. 3 8 1 . 8 3 )

5 5 h / d a y

1 . 2 0 ( 0

. 5 8 2 . 4 9 )

p e r 2 h / d a y

1 . 0 2 ( 0

. 7 8 1 . 3 3 )

R i d i n g i n a c a r

W a r r e n

e t a

l .

2 0 1 0 4 5

7 7 4 4 m e n ,

4 7 . 1

y e a r s

3 7 7 C V

d e a t h s


s t r o k e

, c a n c e r

2 1

Q 1

1 . 0 0

A g e ,



,



L e i s u r e

a n d w o r k p h y s i c a l

a c t i v i t y r a t e d r e l a t i v e t o

o t h e r s .

W a s d i c h o t o m i z e d

i n t o p h y s i c a l l y a c t i v e v s

i n a c t i v e

Q 2

1 . 0 9 ( 0

. 7 8 1 . 5 2 )

Q 3

1 . 2 3 ( 0

. 8 9 1 . 7 0 )

Q 4

1 . 5 0 ( 1

. 0 8 2 . 0 9 )

C H

D c o r o n a r y h e a r t d i s e a s e ; C V

c a r d i o v a s c u l a r ; C V D

c a r d i o v a s c u l a r d i s e a s e ; M

I m y o c a r d i a l i n f a r c t i o n .



8/16

of 7744 men in the Aerobics Center Lon gitudinalStudy (ACLS) identified 377 CVD deaths. 45 Whencomparing the top with lowest quartiles, the authorsnoted an aHR of 0.96 (95% CI: 0.681.36) for watch-ing television and an aHR of 1.50 (95% CI: 1.082.09)for riding in a car.

In the Australian Diabetes, Obesity and LifestyleStudy, 8800 men and women aged 25 years or olderhad a median follow-up of 6.6 years during which284 participants died (87 CVD deaths). 46 Participantsreported time spent watching television or videosduring the previous 7 days excluding time spent inactivities while the television was on. Although thereliability of reported screen time was good( 0.82), the criterion validity was poor ( 0.3).Comparing those who reported watching televisionfor 5 4 h/day vs


9/16

adjusted for several cardiometabolic factors, whichcould be considered to be mediating variables, yieldedthe highest risk estimates. A very recent meta-analysisof the first four studies yielded a summary relativerisk for fatal or non-fatal CVD of 1.15 (95% C I:1.061.23) per 2 h/day prolonged television viewing. 20

Updating the result from that analysis with resultsfrom the two most recent studies yields a fixed effectssummary HR per 2 h/day of screen time of 1.17 (95%CI: 1.131.20; test for heterogeneity: Q 2.61, P 0.760; I 2 0%) (Figure 4 ). Because of its largesize, the NIH-AARP study dominates the analysis.Once excluded, the summary HR was 1.14 (95% CI:1.051.22; test for heterogeneity: Q 1.95, P 0.745; I 2 0%).

Does adequate physical activity mitigate

the possible harmful effects of excessivesedentary behaviour?Several prospective studies tried to address this issueby stratif ying analyses by physical activity sta-tus. 16 ,43 ,45 Researchers stratified participants of the CPS II into five physical activity levels (


10/16

related to concentrations of triglycerides and less so toBMI, waist circumference, and 2-h plasma glucose. 49

More recently, analyses of 4757 American adults aged20 years or older revealed that the number of breaksin sedentary time measured by accelerometer wasinversely proportional to t he waist circumferenceand C-reactive protein levels. 50

MechanismsRelatively little evidence identifying unique potentialmechanisms for the effect of sedentary behaviour oncardiovascular outcomes exists, especially when highlevels of physical activity also exist. In animal studies,the unloading of hindlimbs in rats produced reversiblereductions of lipoprotein lipase (LPL) activity, which was confined to the affected limbs, and subsequentreductions in the local uptake of triglycerides andcirculating concentr at ions of high-density lipoproteincholesterol (HDLC). 51

Evidence from related areas of investigation may

shed light on the mechanisms that link excessivesedentary behaviour to CVD. Air travel is a mode of transport characterized by prolonged sitting, often incramped spaces. When reports about deep veinthrombosis (DVT) in airline passengers emerged,immediate attention was drawn to the long periodsduring which passengers are required to sit. In arandomized trial, 10% of passengers aged 50 yearsor older on long flights developed asymptomaticDVT.52 Besides prolonged sitting, host factors andairplane cabin environmental factors are thought tocontribute to DVT on long flights.

Bed rest is a step down the MET scale from sitting,and the physiological changes effected by the former

may have relevance to the latter. Prolonged bed restproduces adverse effects on numerous organ systemsincluding the cardiovascular system involvingnegative repercussions on postural hypotension,cardiac function, cardiac filling, stroke volume,cardiac output, heart rate and thromboembolicevents. 5359 These complications may be germane tothe studies of excessive sitting or sedentary behaviourand CVD. Furthermore, bed rest may lead to glucoseintolerance, an important CVD risk factor. 55

DiscussionSince the 1950s, epidemiological studies have sug-gested that sedentary behaviour adversely affectshealth. The landmark systematic review of prospectivestudies by Powell et al. in 1987 conclusively linkedphysical activity to CHD. 60 The review focused largelyon quantifying the dose, intensity and type of physicalactivity needed to produce benefits. After manyadjustments for possible confounding variablesacross studies, the highest levels of physical activityconferred an almost 50% reduction in risk for CVD. At that time, sedentary behaviour was considered to

be at the lower end of a physical activity continuum,even though the amount of sedentary behaviour as-signed to the least active category in studies wasuncertain.

Largely in the past decade, interest has burgeoned instudying the possible health impact of sedentarybehaviour apart from physical activity, perhaps inrecognition of the growing amount of sedentarypursuits in modern society. This different conceptualapproach seeks to address questions of whethersedentary behaviour affects health outcomes at eachlevel of physical activity. Thus, the questions that were asked in the more recent studies differ fromthose considered previously.

The growing number of studies reporting positiveassociations between sedentary behaviour and CVDsuggest that the results are unlikely to be spuriousfindings. Two alternative explanations are that eitherthe findings are true or the findings reflect varioustypes of bias. If true, it may be that sedentary behaviour displaces time spent in light physical activity, with time spent in sedentary behaviours being a lostopportunity to perform substantive amounts of phys-ical activity. 61 However, when several trials sought toreduce television viewing among children, they didnot consis tently improve measured physical activitylevels. 6264 In fact, the links between watching television and poor dietary and snacki ng habits weremore often repeatedly demonstrated. 65 Thus, disen-tangling the possible effects of sedentary behaviourfrom those of unhealthy dietary and snacking behaviour remains a critical challenge before reachingfirm conclusions or stipulating guidelines for costlyinterventions.

LimitationsSeveral limitations deserve consideration. Firstly, the validity and reliability of questions to assess sedentarybehaviour are often unknown. A review of questionsabout television watching concluded that there was variable validity. 66 Less is known about questionsfor assessing sitting particularly outside the work-place. A review of occupational physical activityassessments found sitting questions to be more rel i-ably reported than other work activity questions. 67

Some misclassification of exposure likely exists inmany studies. The degree of misclassification is un-likely to be non-differential because respondents aremore likely to systematically underreport their seden-tary behaviour. In most studies, the reference grouprepresents the least sedentary group. If that groupbecomes populated with participants who actuallyare more sedentary, the baseline risk of the referencegroup increases resulting in underestimating hazardratios.

Secondly, different approaches in selecting referenceand exposure categories in studies complicate com-parisons of their results. For example, in studies of sitting, reference categories were either


11/16

day and the top category ranged from 5 6h/day to5 16 h/day.

Thirdly, most of the reviewed prospective studieshad mortality rather than incidence as their outcome.

Fourthly, because the magnitude of the hazardratios is generally small, unmeasured or incorrectlyspecified confounders are of concern. Because sed-entary behaviour is precisely thata behaviourthere is a great susceptibility to this bias whenphysical activity and dietary behaviours are knownto co-occur as part of broader behavioural pattern.Sedentary individuals and those who are not con-sidered sedentary are likely to differ in a myriad of measurable and immeasurable ways. Physical activ-ity and diet are notoriously difficult to measure ac-curately, adding to the difficulty of appropriatelyspecifying models that might also include factorsas mediating variables. Although several studies adjusted for total energy intake, only a limited numberof studi es adjusted for some kind of dietary pat-tern. 44 , 46 ,48 The observational studies regarding thepurported health benefits of some vitamins havetaught the epidemiological community some painfullessons about extrapolating from observational stu-dies and, thus, appropriate confirmatory studies areneeded.

Fifthly, at the inception of prospective studies,participants who were in poor health may have beenmore sedentary than healthier participants. Attempting to rule out reverse causation, some studiesexcluded from analyses those participants whoexpired within the first few years of follow-up, oftenfinding no change in results. 16 , 47

Sixthly, the factors that govern sedentary status mayalso affect CVD risk. For example, a body of researchhas suggested that persons subject to the combinationof low decision latitude to select their work circum-stances and poor support are likely to occupy jobscharacterized by high levels of stress and sedentari-ness and experience higher morbidity and mortalitythan those in opposing circumstances. 68

UniquenessThe question of whether sedentary behaviour is trulydistinct from physical activity rather than simply re p-resenting one end of the physical activity spectrum 3 ,5

can be examined from the following perspectives:

Energy expenditure: Sedentary behaviouroccupies the lower end of an energy expenditurescale with a range of MET values for associatedactivities ranging from 1.0 to 1.5 or 2.0 METs.Changing posture from motionless sitting tomoti on less standing raises energy expenditure by

9%.69Physiology: A key study showed that localmuscle concentrations of LPL of unloaded hindlegs of rats decreased in function of unloadedtime but increased again when rats were allowed

to use their hind legs. 51 Because LPL serves toregulate lipid concentrations and maintain cardi-ometabolic homeostasis, these findings provideda rationale for relating sedentary behaviour tocardiometabolic aberrations. Unfortunately, fewother studies provide unique physiologicalmechanisms of sedentary behaviour, with nonereplicated in humans.Epidemiology and statistics: Several studieshave found that physical activity and sedentarybehaviour are poorly associated having correl-ation coefficients ranging from 0.002 to

0.09. 43 , 70 ,71 Moreover, risk estimates for seden-tary behaviour and CVD events were oftenindependent of physical activity.Determinants research: It seems plausiblethat sedentary behaviour might arise from aunique set of motivational cues differing sub-stantially or entirely from those that motivatesomeone to engage in physical activity.Research into the determinants of sedentarybehaviour is still young. Intuitively, the seductivenature of technology and its spread, especially aspart of entertainment, is likely a major contribu-tor to sedentary behaviour. Extrapolating beyondavailable empirical evidence is problematical asillustrated by a study that showed that thedegree of neighbourhood walkability correlatedfavorably with physical ac tivity levels 72 but not with sedentary behaviour. 73 In another study,neighbourhood walkability was inversely asso-ciated with tel evision viewing time in womenbut not in men. 74 Hence, determinants of pursu-ing specific sedentary behaviours may be as

unique as those governing why people chooseto walk, pla y tennis, golf or engage in someother activity. 5

Guideline development and risk communi-cation: If sedentary behaviour negatively affectshealth and has a unique set of determinants,then separate recommendations to specificallylimit sedentary behaviour will need to bedeveloped that complement those that addressphysical activity. Currently, specific recommen-dations and risk communication strategies maybe premature and await further evidence con-cerning the frequency, timing and duration of breaks necessary to combat the cardiovascularhealth consequences of excessive sedentarybehaviour.Public health interventions: Public healthapproaches to reduce sedentary behaviour andincrease physical activity in populations arelikely to differ substantially. For example, agreat deal of research has linked attributes of the p hysical environment to physical activitylevels. 75 However, whether modifications to theenvironment that might encourage more physicalactivity would also serve to reduce sedentary



12/16

behaviour is not guaranteed, as some researchintimates.Clinical practice: Because clinical advice topatients to raise their levels of physical activitymay not reduce their sedentary behaviour,clinicians may need to assess for, and counselin response to, the amounts of both physicalactivity and sedentary behaviour of theirpatients.

Public health interventionsMany employed people engage largely in desk work.One option is to find ways to reduce the job-relatedsitting time or find ways to introduce a sufficientnumber of breaks during the day to mitigate excessiverisks from sitting. A recent review offered severaloptions for modifying the work space includingproviding employees with standing desks, a therapyball to sit on, stepping devices and walking workstations. 76 In addition, the authors proposed adding

breaks. However, the frequency and duration of breaks needed to offset any risk of excessive sittingremains unknown and requires investigation.Widespread adoption of measures to break up periodsof prolonged sedentary behaviour at work awaitsrigorous studies concerning the cost-effectiveness of potential interventions.

Because a sizeable portion of waking hours is spentbeing sedentary in ones home, targeting the domesticenvironment is an obvious strategy given that muchof the population may not recognize the possibleadverse impact of that excessive sedentary behaviouron health. Also, as the evidence base concerning howto specifically reduce the domestic sedentary behaviour is scant, some form of education may be neces-sary even though education alone cannot guaranteebehavioural change. With high and increasing levelsof watching television or using computers or oth erforms of screen time in contemporary societies, 77

efforts aimed at decreasing time performing theseactivities in a position other than sitting hold consid-erable appeal. Although studies have successfullyreduced tel evision viewing time by children andadolescents, 62 ,64 relatively little research has includedadults. Consequently, there is a dearth of evidence-based interventions to guide domesticinterventions among adults. The introduction of labour-saving devices in the home was meant, inpart, to free up peoples time to engage in moredesirable leisure-time pursuits. If the unintendedeffect of these devices was to promote sedentarybehaviours, perhaps a return to more traditional ways of performing household chores might provebeneficial to ones health (but perhaps not to onespsyche). Shifting people from one sedentary behaviour such as using a computer to another one suchas reading a book is unlikely to improve health.

Much of the current energy directed towardspublic health interventions at the community level

revolves around changing policies, systems and en- vironments. The models that are being developedand tested specifically seek to raise physical activitylevels in the US population rather than reduce sed-entary behaviour and sitting, per se. Therefore, somerecalibration of these approaches may be required toproduce decreases in sedentary behaviour for Americans.

Because so many people spend so much time com-muting in a car to work as well as using a car forother activities, efforts to promote public transporta-tion and get people to perform errands on foot orby bicycle could reduce the time that people sit mo-tionlessly. However, the MET level of sitting in abus or train vs that of sitting in a car is very simi-lar, so shifting people from transportation by car tothat of mass transit would not necessarily reducesedentary behaviour. Because of limited seating,many people have little choice but to stand inpublic transport systems, which in itself wouldreduce sedentary behaviour. In addition, some add-itional energy expenditure may derive from walking or bicycling to and from public transporta-tion stops.

Clinical interventionsMost American adults have an encounter with themedical system each year with 70% of respondentsof the 2009 Behavioral Risk Factor SurveillanceSystem reporting a routine check-up in the previous year (Ford E, personal observation). These encounterspresent precious opportunities for clinicians to counseltheir patients about the possible benefits of reducingsedentary behaviour and sitting. Participants in a clin-

ical trial who received individual counselling andphysical activity prescriptions reduced their sittingtime an average of 2 h/day, whereas participants who received usual care reduced sitting time1 h/day. 78 It is yet unclear how well-informed phys-icians are about the emerging evidence of the possibleharmful effects of sedentary behaviour. Once therelationship between sedentary behaviour and CVDis better understood and evidence-based clinicalapproaches emerge to mitigate risk, clinicians maybenefit from professional education about routinelyenquiring about their patients sedentary habits andphysical activity levels and providing appropriatecounselling.

Future directionsProspective observational studies are generallyaccorded a high level of confidence in epidemiology.However, fewer than a dozen prospective studies haveexamined the links between various forms of seden-tary behaviour (television watching, riding in a car,sitting, etc.) and risks of fatal or non-fatal CVD.Because the outcome of interest has been almostentirely limited to mortality, additional studies of incident CVD are desirable. Also, self-reported



13/16

questions were used to assess exposure time.Consequently, additional prospective studies areneeded, especially ones using a consistent way tomeasure sedentary behaviour while using less hetero-geneous ways of analysing data. Some degree of standardization, for example of the reference category, would aid in the interpretation of future data and would help to establish the magnitude of the riskreduction and doseresponse relationships.Prospective studies that use accelerometers orother objective methods to measure amounts of sed-entary behaviour may prove valuable in confirmingfindings from the existing prospective studies.Ideally, studies that include more than one assess-ment of sedentary behaviour over time would permitan understanding of increasing, decreasing and sta-tionary levels of sedentary behaviour on healthoutcomes.

Our understanding of ways to break up sedentarytime is in its infancy. To guide the development of rational public health and clinical interventions, thefrequency and duration of such breaks needed tomitigate the harms from excessive sedentary behaviour must be thoroughly understood. Morecross-sectional studies can help guide the design of randomized controlled trials that seek to examinethe frequency and duration of breaks needed toreduce cardiovascular risk. In the occupational setting, workers could be randomized to intervention groupsin which workstations are modified or to a controlgroup in which the work setting remains unchanged.Thereafter, group changes in CVD risk factors, illness,medical costs, work absence and productivity could becompared.

The estimated cost of physical inactivity is high $251 billion in 2003 dollars in USA. 79

Consequently, reducing sedentary behaviour mightproduce substantial reductions in costs, but this sup-position remains to be established empirically. Giventhe increasingly precarious financial plight of federaland state governments, a key consideration in imple-menting future interventions will be theircost-effectiveness. Such research tailored to the USA is urgently needed.

Current physical activity guidelines generally focuson raising the level of physical activity in the popula-tion and do not specifically define precise reductionsof sedentary behaviour. Evidence-based revisions orupdates of future guidelines will allow rational andcost-effective recommendations specific to reducingsedentary behaviour.

ConclusionsConventional wisdom dictates that people have grownmore sedentary during the twentieth and twenty-firstcenturies, but few objective data exist to characterizethe magnitude of the change. Regardless of this pastuncertainty, recent data clearly indicate that the levelof sedentary behaviour in the US population and inother nations with developed economies is quite sub-stantial. Although studies during the 1950s first iden-tified an increase in CVD risk experienced by people

in highly sedentary jobs, only in recent years have thepotential CVD risks from sedentary behaviour, as dis-tinct from physical activity, come to be appreciated.Our review of prospective studies found a significantassociation between screen time and cardiovascularmortality independent of levels of physical activity.Furthermore, two large cohort studies that lent them-selves to a meta-analytic summary also suggested asignificant increased risk between the time spentsitting and cardiovascular mortality, also independentof physical activity. Despite the need to solidify theevidence base concerning the health risks caused byexcessive sedentary behaviour, available data are clearthat being in the least active group is not desirable,especially when excessive sedentary behaviour islikely to comprise membership in that group.

Supplementary DataSupplementary Data are available at IJE online.

Conflict of interest: None declared.

KEY MESSAGES

On average, adults in many societies spend a large portion of their day being sedentary.

A limited number of prospective studies have found that the amount of time being sedentaryforexample time spent sitting or watching televisionis associated with increased risk for fatal andnon-fatal CVD.

Cross-sectional studies showing that the number of breaks in sedentary time is favourably associated with cardiometabolic factors require additional replication and confirmation in experimental studies.

Additional research is needed to clarify the relationships between the amount of time that adults aresedentary and fatal and non-fatal outcomes such as CVD and to develop strategies to mitigate anysuch increased risk.

http://ije.oxfordjournals.org/cgi/content/full/dys078/DC1http://ije.oxfordjournals.org/cgi/content/full/dys078/DC1


14/16

References1 U.S. Department of Health and Human Services, Centers

for Disease Control and Prevention. Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA:National Center for Chronic Disease Prevention andHealth Promotion, 1996.

2 Church TS, Thomas DM, Tudor-Locke C et al. Trends over5 decades in U.S. occupation-related physical activity andtheir associations with obesity. PLoS One 2011;6:e19657.

3 Dietz WH. The role of lifestyle in health: the epidemiologyand consequences of inactivity. Proc Nutr Soc 1996;55:82940.

4 Owen N, Healy GN, Matthews CE, Dunstan DW. Toomuch sitting: the population health science of sedentarybehavior. Exerc Sport Sci Rev 2010;38: 10513.

5 Owen N, Leslie E, Salmon J, Fotheringham MJ.Environmental determinants of physical activity andsedentary behavior. Exerc Sport Sci Rev 2000;28: 15358.

6 Salmon J, Owen N, Crawford D, Bauman A, Sallis JF.Physical activity and sedentary behavior: a population-based study of barriers, enjoyment, and preference. Health Psychol 2003;22: 17888.

7

Chastin SF, Granat MH. Methods for objective measure,quantification and analysis of sedentary behaviour andinactivity. Gait Posture 2010;31: 8286.

8 Ainsworth BE, Haskell WL, Whitt MC et al. Compendiumof physical activities: an update of activity codes and METintensities. Med Sci Sports Exerc 2000;32: S498504.

9 Wareham NJ, Jakes RW, Rennie KL et al. Validity andrepeatability of a simple index derived from the shortphysical activity questionnaire used in the EuropeanProspective Investigation into Cancer and Nutrition(EPIC) study. Public Health Nutr 2003;6:40713.

10 Ekelund U, Brage S, Besson H, Sharp S, Wareham NJ.Time spent being sedentary and weight gain in healthyadults: reverse or bidirectional causality? Am J Clin Nutr 2008;88: 61217.

11

Troiano RP, Berrigan D, Dodd KW, Masse LC, Tilert T,McDowell M. Physical activity in the United Statesmeasured by accelerometer. Med Sci Sports Exerc 2008;40:18188.

12 Metzger JS, Catellier DJ, Evenson KR, Treuth MS,Rosamond WD, Siega-Riz AM. Patterns of objectivelymeasured physical activity in the United States. Med Sci Sports Exerc 2008;40: 63038.

13 Matthews CE, Chen KY, Freedson PS et al. Amount of time spent in sedentary behaviors in the United States,20032004. Am J Epidemiol 2008;167: 87581.

14 van Uffelen JG, Wong J, Chau JY et al. Occupationalsitting and health risks: a systematic review. Am J Prev Med 2010;39: 37988.

15 The Nielsen Company. Three Screen Report. http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers- watch-nielsens-q1-2010-three-screen-report/ (23 June2011, date last accessed).

16 Wijndaele K, Brage S, Besson H et al. Television viewingtime independently predicts all-cause and cardiovascularmortality: the EPIC Norfolk Study. Int J Epidemiol 2011;40: 15059.

17 Dong L, Block G, Mandel S. Activities contributing tototal energy expenditure in the United States: resultsfrom the NHAPS Study. Int J Behav Nutr Phys Act 2004;1:4.

18 Healy GN, Dunstan DW, Salmon J et al. Objectively mea-sured light-intensity physical activity is independently

associated with 2-h plasma glucose. Diabetes Care 2007;30: 138489.

19 McKenzie B, Rapino M. Commuting in the United States:2009. American Community Survey Reports No. ACS-15.Washington, DC: U.S. Census Bureau, 2011.

20 Grontved A, Hu FB. Television viewing and risk of type 2diabetes, cardiovascular disease, and all-cause mortality:a meta-analysis. JAMA 2011;305: 244855.

21 Orsini N, Bellocco R, Greenland S. Generalized leastsquares for trend estimation of summarized doseresponse data. Stata J 2006;6:4057.

22 DerSimonian R, Laird N. Meta-analysis in clinical trials.Control Clin Trials 1986;7:17788.

23 Higgins JP, Thompson SG, Deeks JJ, Altman DG.Measuring inconsistency in meta-analyses. BMJ 2003;327: 55760.

24 Morris JN, Heady JA, Raffle PA, Roberts CG, Parks JW.Coronary heart-disease and physical activity of work. Lancet 1953;265: 111120.

25 Taylor HL, Klepetar E, Keys A, Parlin W, Blackburn H,Puchner T. Death rates among physically active andsedentary employees of the railroad industry. Am J Public Health Nations Health 1962;52: 1697707.

26 Netterstrom B, Laursen P. Incidence and prevalence of ischaemic heart disease among urban bus drivers inCopenhagen. Scand J Soc Med 1981;9:7579.

27 Balarajan R, McDowall ME. Professional driversin London: a mortality study. Br J Ind Med 1988;45:48386.

28 Paradis G, Theriault G, Tremblay C. Mortality in ahistorical cohort of bus drivers. Int J Epidemiol 1989;18:397402.

29 Michaels D, Zoloth SR. Mortality among urban busdrivers. Int J Epidemiol 1991;20: 399404.

30 Alfredsson L, Hammar N, Hogstedt C. Incidence of myocardial infarction and mortality from specific causesamong bus drivers in Sweden. Int J Epidemiol 1993;22:5761.

31 Merlo DF, Stagi E, Fontana V et al. A historical mortalitystudy among bus drivers and bus maintenance workersexposed to urban air pollutants in the city of Genoa, Italy.Occup Environ Med 2010;67: 61119.

32 Holme I, Helgeland A, Hjermann I, Leren P, Lund-Larsen PG. The Oslo study: 4-year mortality, coronaryrisk factors and socioeconomic indicators. Tidsskr Nor Laegeforen 1980;100: 126266.

33 Rosengren A, Anderson K, Wilhelmsen L. Risk of coronary heart disease in middle-aged male bus andtram drivers compared to men in other occupations: aprospective study. Int J Epidemiol 1991;20: 8287.

34 Sjol A, Thomsen KK, Schroll M, Andersen LB. Seculartrends in acute myocardial infarction in relation tophysical activity in the general Danish population. Scand J Med Sci Sports 2003;13: 22430.35 Hu G, Sarti C, Jousilahti P, Silventoinen K, Barengo NC,Tuomilehto J. Leisure time, occupational, and commutingphysical activity and the risk of stroke. Stroke 2005;36:199499.

36 Hu G, Jousilahti P, Borodulin K et al. Occupational, com-muting and leisure-time physical activity in relation tocoronary heart disease among middle-aged Finnish menand women. Atherosclerosis 2007;194: 49097.

37 Hu G, Tuomilehto J, Borodulin K, Jousilahti P. The joint associations of occupational, commuting, andleisure-time physical activity, and the Framingham risk

http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/http://blog.nielsen.com/nielsenwire/online_mobile/what-consumers-watch-nielsens-q1-2010-three-screen-report/


15/16

score on the 10-year risk of coronary heart disease. Eur Heart J 2007;28: 49298.

38 Rosenman RH, Bawol RD, Oscherwitz M. A 4-yearprospective study of the relationship of different habitual vocational physical activity to risk and incidence of ische-mic heart disease in volunteer male federal employees. Ann N Y Acad Sci 1977;301: 62741.

39 Johansson S, Rosengren A, Tsipogianni A, Ulvenstam G,Wiklund I, Wilhelmsen L. Physical inactivity as a riskfactor for primary and secondary coronary events inGoteborg, Sweden. Eur Heart J 1988;9:819.

40 Li CY, Sung FC. A review of the healthy worker effect inoccupational epidemiology. Occup Med (Lond) 1999;49:22529.

41 Manson JE, Greenland P, LaCroix AZ e t al. Walkingcompared with vigorous exercise for the prevention of cardiovascular events in women. N Engl J Med 2002;347:71625.

42 Katzmarzyk PT, Church TS, Craig CL, Bouchard C. Sittingtime and mortality from all causes, cardiovasculardisease, and cancer. Med Sci Sports Exerc 2009;41: 9981005.

43 Patel AV, Bernstein L, Deka A et al. Leisure time spentsitting in relation to total mortality in a prospectivecohort of US adults. Am J Epidemiol 2010;172: 41929.

44 Matthews CE, George SM, Moore SC et al. Amount of time spent in sedentary behaviors and cause-specificmortality in US adults. Am J Clin Nutr 2012;95: 43745.

45 Warren TY, Barry V, Hooker SP, Sui X, Church TS,Blair SN. Sedentary behaviors increase risk of cardiovas-cular disease mortality in men. Med Sci Sports Exerc 2010;42: 87985.

46 Dunstan DW, Barr EL, Healy GN et al. Television viewingtime and mortality: the Australian Diabetes, Obesity andLifestyle Study (AusDiab). Circulation 2010;121: 38491.

47 Stamatakis E, Hamer M, Dunstan DW. Screen-basedentertainment time, all-cause mortality, and cardiovascu-lar events: population-based study with ongoing mortalityand hospital events follow-up. J Am Coll Cardiol 2011;57:29299.48 Ford ES. Combined television viewing and computer useand mortality from all-causes and diseases of the circu-latory system among adults in the United States. BMC Public Health 2012;12: 70.

49 Healy GN, Dunstan DW, Salmon J et al. Breaks in seden-tary time: beneficial associations with metabolic risk. Diabetes Care 2008;31: 66166.

50 Healy GN, Matthews CE, Dunstan DW, Winkler EA,Owen N. Sedentary time and cardio-metabolic bio-markers in US adults: NHANES 200306. Eur Heart J 2011;32: 59097.

51 Bey L, Hamilton MT. Suppression of skeletal musclelipoprotein lipase activity during physical inactivity: amolecular reason to maintain daily low-intensity activity. J Physiol 2003;551: 67382.52 Scurr JH, Machin SJ, Bailey-King S, Mackie IJ,McDonald S, Smith PD. Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights:a randomised trial. Lancet 2001;357: 148589.

53 Persson AV, Davis RJ, Villavicencio JL. Deep venousthrombosis and pulmonary embolism. Surg Clin North Am 1991;71: 1195209.

54 Dittmer DK, Teasell R. Complications of immobil-ization and bed rest. Part 1: musculoskeletal andcardiovascular complications. Can Fam Physician 1993;39:142837.

55 Teasell R, Dittmer DK. Complications of immobilizationand bed rest. Part 2: other complications. Can Fam Physician 1993;39: 144046.

56 Rousseau P. Immobility in the aged. Arch Fam Med 1993;2:16977.

57 Krasnoff J, Painter P. The physiological consequences of bed rest and inactivity. Adv Ren Replace Ther 1999;6:12432.

58 Kyrle PA, Eichinger S. Deep vein thrombosis. Lancet 2005;365: 116374.

59 English KL, Paddon-Jones D. Protecting muscle mass andfunction in older adults during bed rest. Curr Opin Clin Nutr Metab Care 2010;13: 3439.

60 Powell KE, Thompson PD, Caspersen CJ, Kendrick JS.Physical activity and the incidence of coronary heartdisease. Annu Rev Public Health 1987;8:25387.

61 Williams DM, Raynor HA, Ciccolo CT. A review of TV viewing and its association with health outcomes inadults. Am J Lifestyle Med 2008;2:25059.

62 Robinson TN. Reducing childrens television viewing toprevent obesity: a randomized controlled trial. JAMA1999;282: 156167.

63 Ford BS, McDonald TE, Owens AS, Robinson TN. Primarycare interventions to reduce television viewing in African-American children. Am J Prev Med 2002;22:10609.

64 Epstein LH, Roemmich JN, Robinson JL et al. A rando-mized trial of the effects of reducing television viewingand computer use on body mass index in young children. Arch Pediatr Adolesc Med 2008;162: 23945.

65 Simoes EJ, Byers T, Coates RJ, Serdula MK, Mokdad AH,Heath GW. The association between leisure-time physicalactivity and dietary fat in American adults. Am J Public Health 1995;85: 24044.

66 Clark BK, Sugiyama T, Healy GN, Salmon J,Dunstan DW, Owen N. Validity and reliability of measures of television viewing time and other non-occupational sedentary behaviour of adults: a review.Obes Rev 2009;10: 716.67 Ainsworth BE, Jacobs DR Jr, Leon AS, Richardson MT,Montoye HJ. Assessment of the accuracy of physicalactivity questionnaire occupational data. J Occup Med1993;35: 101727.

68 Karasek R, Baker D, Marxer F, Ahlbom A, Theorell T. Jobdecision latitude, job demands, and cardiovasculardisease: a prospective study of Swedish men. Am J Public Health 1981;71: 694705.

69 Levine JA, Schleusner SJ, Jensen MD. Energy expenditureof nonexercise activity. Am J Clin Nutr 2000;72: 145154.

70 Hu FB, Li TY, Colditz GA, Willett WC, Manson JE.Television watching and other sedentary behaviors inrelation to risk of obesity and type 2 diabetes mellitusin women. JAMA 2003;289: 178591.

71

Healy GN, Dunstan DW, Salmon J, Shaw JE, Zimmet PZ,Owen N. Television time and continuous metabolic risk inphysically active adults. Med Sci Sports Exerc. 2008;40:63945.

72 Van Dyck D, Cardon G, Deforche B, Sallis JF, Owen N,De Bourdeaudhuij I. Neighborhood SES and walkabilityare related to physical activity behavior in Belgian adults. Prev Med 2010;50: S7479.

73 Van Dyck D, Cardon G, Deforche B, Owen N, Sallis JF,De Bourdeaudhuij I. Neighborhood walkability andsedentary time in Belgian adults. Am J Prev Med 2010;39: 2532.



16/16

74 Sugiyama T, Salmon J, Dunstan DW, Bauman AE, Owen N.Neighborhood walkability and TV viewing time among Australian adults. Am J Prev Med 2007;33: 44449.

75 Frank LD, Andresen MA, Schmid TL. Obesity relation-ships with community design, physical activity, andtime spent in cars. Am J Prev Med 2004;27: 8796.

76 Chau JY, van der Ploeg HP, van Uffelen JG et al. Are workplace interventions to reduce sitting effective? A systematic review. Prev Med 2010;51: 35256.

77 Braun J. One Television Year in the World. http://www.international-television.org/tv_market_data/world-tv-

programme-viewing-trends-2009 html (1 March 2012,date last accessed).

78 Kallings LV, Sierra Johnson J, Fisher RM et al. Beneficialeffects of individualized physical activity on prescriptionon body composition and cardiometabolic risk factors:results from a randomized controlled trial. Eur J Cardiovasc Prev Rehabil 2009;16: 8084.

79 Chenoweth D, Leutzinger J. The economic cost of physicalinactivity and excess weight in American adults. J Phys Act Health 2006;3:14863.

Published by Oxford University Press on behalf of the International Epidemiological Association The Author 2012; all rights reserved. Advance Access publication 12 September 2012

International Journal of Epidemiology 2012;41 :13531355doi:10.1093/ije/dys128

Commentary: Too much sittinga publichealth threat?Ulf Ekelund 1,2

1 Department of Sport Medicine, Norwegian School of Sport Science, Oslo, Norway and 2 Medical Research Council EpidemiologyUnit, Institute of Metabolic Science, Addenbrookes Hospital, Cambridge, UK

*Corresponding author. Department of Sport Medicine, Norwegian School of Sport Sciences, PO Box 4014, Ulleva l Stadion, 0806Oslo, Norway. E-mail: [email protected]

Accepted 10 July 2012

As exemplified by two articles1 ,2

in this issue of the journal, there has been an almost exponential interestin researching the potential detrimental health effectsof sedentary behaviour during the past few years.Sedentary behaviour is a distinct behaviour, not syn-onymous with physical inactivity, and defined as any waking behaviour characterized by an energy expend-iture 4 1.5Metabo lic Equivalents while in a sitting orreclining position. 3 According to this definition, beingsedentary has two prerequisites: the type of behav-iour, i.e. sitting or reclining, combined with lowenergy expenditure. Although robust secular trenddata on sedentary time are unavailable, it is likelythat population levels of total sedentary time haveincreased during the past 50 years, possibly owingto an increase in occupational- and transport-relatedsedentary time.

The vast majority of studies examining the healthimpact of sedentary time has been observational indesign, and most of these addressed the associationsbetween TV viewing and health outcomes. 1 This is notsurprising, as TV viewing constitutes the dominantleisure time of sedentary behaviour in many developed countries, including Australia, UK and theUSA. However, TV viewing is a specific sedentary

behaviour and may not be a marker of overall seden-tary time. In addition, TV viewing may be associated with a generally unhealthy lifestyle difficult to statis-tically control for in any observational study.

Ford and Caspersen 1 reviewed prospective observa-tional cohort studies that reported on the associationsbetween total sitting time and TV viewing with fataland non-fatal cardiovascular disease (CVD). Total sit-ting time was consistently associated with increasedrisk for fatal and non-fatal CVD diseases in all fourstudies included in the review. Similar observation s were also recently reported by van der Ploeg et al.4

who demonstrated an increased risk of all-cause mor-tality with increased total sitting time, an associationthat appeared unaffected by sex, age, body massindex (BMI) and physical activity levels. The majorityof studies (four of six) in the review by Ford andCaspersen 1 also showed that higher amounts of timespent viewing TV were associated with increased riskof CVD mortality. The pooled risk ratio was increasedby 17% for each additional 2 h in front of the TV ,similar to another recent meta-analysis on this topic. 5

In a second contribution in this issue, Stamatakiset al.2 report on the cross-sectional associations be-tween self-reported and objectively measured

SEDENTARY BEHAVIOUR 1353
http://localhost/var/www/apps/conversion/tmp/scratch_3/http://localhost/var/www/apps/conversion/tmp/scratch_3/http://localhost/var/www/apps/conversion/tmp/scratch_3/http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://localhost/var/www/apps/conversion/tmp/scratch_3/http://localhost/var/www/apps/conversion/tmp/scratch_3/http://localhost/var/www/apps/conversion/tmp/scratch_3/

Documents

Int. J. Epidemiol.-2012-Ford-1338-53