Association Between Various Sedentary Behaviours and All-Cause, Cardiovascular Disease and Cancer Mortality

The Multiethnic Cohort Study

Yeonju Kim; Lynne R Wilkens; Song-Yi Park; Marc T Goodman; Kristine R Monroe; Laurence N Kolonel

Disclosures

Int J Epidemiol. 2013;42(4):1040-1056. 

In This Article

Results

Characteristics of the Study Subjects

Table 1 shows the distributions of the study participants on several demographic and exposure characteristics by sex and race/ethnicity. Whites, Japanese Americans and Latinos comprised about 20–30% each of our study population, followed by African Americans (15%) and Native Hawaiians (7.5%). The mean age at cohort entry was 58.7 and 58.5 years in men and women, respectively. Among the five ethnic groups, both in men and women, African Americans were less physically active, were more likely to be current smokers and had a higher prevalence of hypertension and/or diabetes. Whites and Japanese were more likely to have a college education than other ethnic groups, among both men and women.

Table 2 compares men and women on the various sedentary behaviours by several subgroup strata. Time spent sitting watching TV was similar between the sexes. Women reported longer durations for sitting doing other leisure activities and at work, whereas men spent more time sitting in a car or bus. For both sexes, African Americans spent more time on average sitting watching TV, whereas Whites and Japanese spent more time sitting at work. On average, men and women who were older, had less education, had higher BMIs, were more likely to be current smokers, were less physically active and consumed fewer fruits and vegetables spent more time sitting watching television. Men and women who had higher BMIs also spent more time sitting in a car or bus and sitting at work. Younger men and those with more education spent longer durations sitting at work. Men and women with higher energy intakes sat longer at meals (data not shown).

Total Daily Sitting Time and Mortality

In the fully adjusted model, total daily sitting was not associated with all-cause mortality, cardiovascular disease mortality or cancer mortality for men, but there was a suggested increase in 'all other causes' mortality (Table 3). Among women, total daily sitting of 10 h per day or more was associated with an increased risk for all-cause mortality (Hazard Ratio (HR) 1.11, 95% Confidence Interval (CI) 1.04–1.19) compared with <5 h/day. There was also an increased risk of mortality from cardiovascular disease and from 'all other causes' among women that was markedly different from the null association for mortality from cancer [P's for heterogeneity <0.01 (global and all pairwise)].

Time Spent in Specific Sitting Categories and Mortality

Table 4 shows the associations between mortality and sitting duration, by type of sitting. The associations with all-cause mortality were statistically different between sitting types based on the differential effects models (P < 0.01 for both men and women). Sitting watching TV had a stronger effect than did other sitting behaviours both in men and women (P < 0.001 for all paired comparisons).

For time spent 'sitting watching TV', the HRs for all-cause mortality in the highest exposure level were 1.19 (95% CI 1.10–1.29) among men and 1.32 (95% CI 1.21–1.44) among women for the fully adjusted model (Table 4). 'Sitting in a car or bus' and 'sitting at work' were not associated with the risk of mortality, whereas 'sitting in other leisure activities' and 'sitting at meals' showed a pattern similar to that for 'sitting watching television'. In further analysis, when men and women who reported 'zero' 'hours sitting at work' were included in the analysis in the reference group, those sitting ≥5 h/day hours at work (vs <1 h/day including zero) and younger than 65 years at baseline had reduced risks of all-cause mortality [men: HR 0.88 (95% CI 0.81–0.95); women: HR 0.86 (95% CI 0.79–0.94)], but no associations were observed among men and women aged 65 and over (P for interaction <0.001 both for men and for women). In general, the associations by cause of mortality were similar to overall mortality, although they varied somewhat in magnitude. However, the HRs for sitting watching TV, in other leisure activities and at meals were the lowest for cancer for both men and women (P for heterogeneity <0.01).

In stratified analyses, for time spent sitting watching television (Table 5), the HRs for the highest exposure category (sitting watching TV ≥ 5 h/day) were generally increased (HR > 1) for all subgroups. Nevertheless, many of the P-values for interaction were less than 0.01, reflecting differences in strengths of the associations across subgroups. The exceptions where the HRs were not elevated were the Japanese American subgroup in men and women, and the underweight (BMI < 18.5) among men, which may be a chance finding due to the small numbers of deaths. In stratified analyses for time spent sitting at work, 'sitting at work' was not associated with mortality in either men or women in any stratum defined by age (<65 y and ≥65 y) or by educational level (lower than college vs college or graduate school) that may reflect type of employment (data not shown).

The patterns of the associations by specific cause of death were generally similar to those of the broader causes of death categories shown in Table 5, although more time spent sitting watching TV was associated with mortality from prostate cancer in men (HR 1.39 (≥5 h/day vs <1 h/day), P for trend <0.01) (supplementary data available at IJE online).

In our sensitivity analysis excluding men and women who died within 5 years of follow-up, the findings were basically unchanged, though some of the HRs comparing ≥5 h/day of sitting watching TV vs <1 h/day were somewhat weakened: all-cause, HR 1.14 (95% CI 1.04–1.25) for men and HR 1.30 (95% CI 1.18–1.43) for women; cardiovascular, HR 1.15 (95% CI 0.98–1.34) for men and HR 1.37 (95% CI 1.16–1.63) for women; 'all other', HR 1.12 (95% CI 0.96–1.32) for men and HR 1.46 (95% CI 1.23–1.73) for women.

Joint Effect of Different Sedentary Behaviours on Mortality

Since several sedentary behaviours were associated with increased mortality, we examined whether combinations of prolonged sitting activities augment the risk of mortality. Table 6 gives the hazard ratios for all-cause mortality by duration spent sitting watching TV and in other sitting activities, with the statistical test for interaction based on the differential effects model. As expected, longer durations spent sitting watching TV coupled with sitting longer in other behaviours led to stronger associations with mortality among both men and women. The only combination that led to an increased risk above that expected was sitting watching TV and sitting at meals.

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