Daily activity energy expenditure and mortality among older adults

Context Exercise is associated with mortality benefits but simply expending energy through any activity in an individual's free-living environment may confer survival advantages. Objective To determine whether free-living activity energy expenditure is associated with all-cause mortality among older adults. Design, Setting, and Participants Free-living activity energy expenditure was assessed in 302 high-functioning, community-dwelling older adults ( aged 70-82 years). Total energy expenditure was assessed over 2 weeks using doubly labeled water. Resting metabolic rate was measured using indirect calorimetry and the thermic effect of meals was estimated at 10% of total energy expenditure. Free-living activity energy expenditure was calculated as: ( total energy expenditure x 0.90) resting metabolic rate. Participants were followed up over a mean of 6.15 years (1998-2006). Main Outcome Measures Free-living activity energy expenditure ( 3 tertiles: low, < 521 kcal/d; middle, 521- 770 kcal/d; high, > 770 kcal/d) and all-cause mortality. Results Fifty-five participants (18.2%) died during follow-up. As a continuous risk factor, an SD increase in free-living activity energy expenditure ( 287 kcal/d) was associated with a 32% lower risk of mortality after adjusting for age, sex, race, study site, weight, height, percentage of body fat, and sleep duration ( hazard ratio, 0.68; 95% confidence interval, 0.48-0.96). Using the same adjustments, individuals in the highest tertile of free-living activity energy expenditure were at a significantly lower mortality risk compared with the lowest tertile ( hazard ratio, 0.31; 95% confidence interval, 0.14-0.69). Absolute risk of death was 12.1% in the highest tertile of activity energy expenditure vs 24.7% in the lowest tertile; absolute risks were similar to these for tertiles of physical activity level. The effect of free-living activity energy expenditure changed little after further adjustment for self-rated health, education, prevalent health conditions, and smoking behavior. According to self-reports, individuals expending higher levels of free-living activity energy were more likely to work for pay ( P=. 004) and climb stairs ( P=. 01) but self-reported high-intensity exercise, walking for exercise, walking other than for exercise, volunteering, and caregiving did not differ significantly across the activity energy expenditure tertiles. Conclusions Objectively measured free-living activity energy expenditure was strongly associated with lower risk of mortality in healthy older adults. Simply expending energy through any activity may influence survival in older adults.