Daily activity energy expenditure and mortality among older adults.
BACKGROUND
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.


METHODS
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).


METHODS
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.
Manini
Todd M
TM
National Institute on Aging, Laboratory of Epidemiology, Demography and Biometry, Bethesda, Md 20892, USA. maninit@mail.nih.gov
Everhart
James E
JE
Patel
Kushang V
KV
Schoeller
Dale A
DA
Colbert
Lisa H
LH
Visser
Marjolein
M
Tylavsky
Frances
F
Bauer
Douglas C
DC
Goodpaster
Bret H
BH
Harris
Tamara B
TB
D000203:Activities of Daily Living; D000368:Aged; D000369:Aged, 80 and over; D001481:Basal Metabolism; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D009026:Mortality; D009043:Motor Activity; D012306:Risk