Motion and Mortality
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips serves on the speaker's bureau of Cephalon, Boehringer Ingelheim, Merck, ResMed, and GlaxoSmithKline, and is a consultant for Boehringer Ingelheim, Wyeth-Ayerst, and ResMed.
Synopsis: Expending energy though any activity may reduce mortality in older adults.
Source: Manini TM, et al. Daily activity energy expenditure and mortality among older adults. JAMA. 2006;296:171-179.
This study was a prospective, 6-year follow-up of 302 people who were between 70 and 82 years of age at the beginning of the study. They were recruited from the ongoing Health, Aging, and Body Composition study cohort assembled through the Universities of Pittsburgh and Tennessee. Total energy expenditure was measured using the doubly labeled water technique1 over a 2-week period. Resting metabolic rate was calculated using indirect calorimetry.2 Free-living activity energy expenditure was calculated using the total energy expenditure and resting metabolic rate,3 using a standard formula. The participants also self-reported physical activity over a 7-day period. Height, weight and body fat were measured with precision, and detailed sociodemographic and medical history information was collected. Participants were followed for an average of 6.1 years; death was ascertained by phone contact every 6 months and verified by death certificates.
The average age of the assembled cohort was 74.8 years; 48.3% were black, 50.3% were women, and 46% were from Pittsburgh. Women had lower levels of energy expenditure than men (251 vs 769 kcals/day). Participants with the highest level of active energy expenditure were more likely to be from Pittsburgh and had a higher body mass index, but a lower percentage of body fat.
The cumulative mortality over 6 years of follow-up was 18.2% (43.2/1000 for men and 27.3/1000 for women). After adjusting for multiple confounders (including body mass index and baselines health status), there was an inverse linear relationship between activity energy expenditure and mortality. The absolute risk for mortality in the highest, middle and lowest levels of activity were 12.1%, 17.6%, and 24.7%, respectively. Every 287 kcal/day energy expenditure lowered the 6-year mortality rate by about 30%, regardless of intensity of activity reported. Those who reported working for pay and climbing stairs were more likely to be in the higher energy expenditure category. There was good correlation between both duration and intensity of self-reported physical activity and free-living activity energy expenditure; intensity of activity or exercise did not predict or confer survival.
This study confirms many previous observational studies that have demonstrated reduced mortality in adults who exercise. What is new and important about this work is that it demonstrates that physical activity which might not be "counted" as exercise confers survival benefit. Simply burning up calories by moving around (which was objectively measured in this study) can delay death. This appears to contradict the belief that exercise must be carried out at a specific intensity to reduce mortality.4 The authors estimated that performing 1¼ hours of a variety of activities, including housework, child care, walking at 2.5 miles/hour, will expend 287 kcals.
While it is possible that those who were sicker were less likely to be active, the investigators rigorously controlled for this possibility, and noted that both self-assessed and clinically determined health status was not significantly different across activity levels.
This paper confirms that longer life now joins a long list of benefits conferred by physical activity in older people, including reduced coronary heart disease,5 cancer,6 falls,7 and dementia.8
In the accompanying editorial, Blair and Haskell point out that fitness may be a stronger predictor of mortality than physical activity per se.9 They also clarify that a substantial difference in energy expenditure in those who were most active was accounted for by "nonexercise activity thermogenesis (NEAT),"10,11 which includes fidgeting, gum-chewing, maintenance of posture, and other physical activities of daily life. NEAT is a hot topic among obesity researchers, as it appears to account for some of the huge variability in human weight gain associated with overeating. The current paper suggests that NEAT has an important role in longevity as well.
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