Leisure Time Spent Sitting in Relation to Total Mortality in a Prospective Cohort of US Adults

Alpa V. Patel; Leslie Bernstein; Anusila Deka; Heather Spencer Feigelson; Peter T. Campbell; Susan M. Gapstur; Graham A. Colditz; Michael J. Thun

Disclosures

American Journal of Epidemiology. 2010;172(4):419-429. 

In This Article

Results

We observed 11,307 deaths in men and 7,923 in women over the 1,610,728 person-years of follow-up. Men and women who spent the least leisure time sitting were leaner, more likely to have never smoked cigarettes, more likely to be employed, and had lower total energy intake (Table 1). Leisure time spent sitting was not associated with physical activity (r = –0.03). Study participants generally engaged in light- to moderate-intensity activities, such as walking for exercise, gardening, shopping, and housework. Moderate- to vigorous-intensity activities were relatively uncommon in this older population; 83% of men and 87% of women reported walking for exercise, and 37% of men and 36% of women listed walking as their only form of recreational physical activity.

Associations of leisure time spent sitting, physical activity, and their combined effects with mortality are shown in Table 2. After multivariate adjustment, leisure time spent sitting was positively associated with all-cause mortality rates in both women and men; however, associations appeared stronger in women (for ≥6 vs. <3 hours/day, relative risk = 1.37, 95% confidence interval (CI): 1.27, 1.47) than men (relative risk = 1.18, 95% CI: 1.12, 1.25) (P heterogeneity = 0.003). After further adjustment for physical activity, these associations remained virtually unchanged. There was a dose-related, inverse relation between physical activity and mortality rates in women and in men beginning at relatively low levels of activity (Table 2). Risk estimates for physical activity similarly were virtually unchanged after further adjustment for time spent sitting.

When examining the combined effects of time spent sitting and physical activity on all-cause death rates, time spent sitting was associated with increased risk regardless of level of physical activity (Figures 1 and 2). The relative risks for the joint effects of sitting and physical activity (≥6 hours/day sitting and <24.5 MET-hours/week activity) were 1.94 (95% CI: 1.70, 2.20) and 1.48 (95% CI: 1.33, 1.65), for women and men respectively, compared with women and men who reported both sitting the least (<3 hours/day) and being the most physically active (≥52.5 MET-hours/week).

Figure 1.

Combined multivariate-adjusted rate ratios (P < 0.05) for leisure time spent sitting and physical activity in relation to all-cause mortality, women only, in the Cancer Prevention Study II Nutrition Cohort, 1993–2006. MET, metabolic equivalent.

Figure 2.

Combined multivariate-adjusted rate ratios (P < 0.05) for leisure time spent sitting and physical activity in relation to all-cause mortality, men only, in the Cancer Prevention Study II Nutrition Cohort, 1993–2006. MET, metabolic equivalent.

We examined the association between time spent sitting and total mortality in men and women combined, stratified by body mass index (Table 3). Although time spent sitting and physical activity were more strongly associated with mortality among lean persons (for time spent sitting, P interaction = 0.06; for physical activity, P interaction = 0.002), both measures were significantly associated with risk of total mortality regardless of body mass index. No other factors examined, including smoking status or attained age, appeared to modify the associations between time spent sitting and physical activity in relation to total mortality (data not shown). Results from the sensitivity analysis among participants who are retired or homemakers also did not differ from those in the overall cohort (data not shown).

Although we excluded the first year of follow-up and prevalent disease, we further examined whether observed associations were a result of unidentified prevalent illness in 2 ways. First, we examined the associations between baseline exposures stratified by follow-up time. Although associations were slightly attenuated, they persisted and remained statistically significant over the 14-year follow-up (data not shown). Second, we conducted a sensitivity analysis combining questions about sitting time and physical activity at baseline with those from our first follow-up survey in 1997 to examine sustained (5-year) measures. Results from these analyses did not differ from those presented for baseline alone (data not shown).

Associations between time spent sitting and physical activity were stronger for cardiovascular disease mortality than for cancer (Table 4). Time spent sitting was associated with an increased risk of cardiovascular disease mortality in both men and women, whereas it was associated with increased cancer mortality only among women. There was a statistically significant inverse relation between physical activity and cardiovascular disease mortality beginning at relatively low levels of activity in both men (P trend = 0.0001) and women (P trend < 0.0001). In contrast, total physical activity was not significantly associated with lower cancer mortality among men and only modestly associated with lower cancer mortality in women. Longer time spent sitting was associated with higher death rates from all other causes, and physical activity was inversely associated with death rates from other causes. The most common conditions in this category were respiratory diseases (22.7% in men, 20.4% in women), central nervous system diseases (20.3% in men, 19.8% in women), digestive diseases (9.6% in men, 10.4% in women), and diabetes (7.8% in men, 6.3% in women).

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