Mortality in older adults in relation to daily activity energy expenditure

The authors of the article forming the basis of this mortality abstract refer to past observational studies, which have shown that older subjects with limited daily activity have a higher mortality than those with greater physical activity. However, in these studies degree of activity was assessed by answers to a questionnaire. The authors of the source article utilized an isotopic method that measured total energy expediture (TEE), from which daily activity energy expenditure (DAEE) could be derived, after measurement of basal metabolic rate (BMR) and adjustment for the thermic energy of meals. The equation used for this derivation is: DAEE = 0.9TEE - BMR.

Expected 7-year survival rates were calculated from the 1989-1991 US Life Tables, and from these mean annual survival and mortality rates were derived as geometric means, for white male, white female, nonwhite male and nonwhite female cohorts, with age 75 the initial age and age 82 the terminal age. There were minor race differences but major sex differences in the race/sex distribution in each DAEE group; the weighting calculations are described in detail. Weighting is utilized not only for the expected but also for the observed mean annual rates. Mean annual mortality rates per 1000 person-years are given in the article, but no exposure data. Exposure has been estimated as E = d/(decimal q).

The 302 patients followed were divided into approximately equal groups, but the proportion of females was highest (71/101) in the group with lowest DAEE, 53/102 in the middle DAEE group, and only 26/99 in the group with maximum DAEE. The disparity in sex distribution resulted in a disparity in expected mortality and the need to adjust the observed survival and mortality rates. The group with the highest DAEE (> 770 kcal/ day) had the lowest adjusted annual mortality rate (21.2 deaths per 1000 person-years). This was used as the reference "expected" mortality rate for the intergroup comparisons of excess mortality. The excess death rate (EDR) for the group with intermediate DAEE (521-770 kcal/day) was 7.3 extra deaths per 1000 per year; the EDR for the group with lowest DAEE (< 521 kcal) was 14.8 per 1000 per year. When mortality in the total cohort of 302 subjects was compared with that expected in the matched US population, the mortality ratio was only 49%, and the EDR was -31 per 1000 per year.