Aging and the Elderly

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A number of studies have investigated whether age modifies the relation between body weight and mortality. Certainly several studies of BMI and mortality among older adults have reported weak effects of obesity on mortality rate and/or very high nadirs for the BMI-mortality curves (38,41,48-50). The Build Study (51) found that the relation between BMI and mortality was U-shaped, and that the BMI associated with minimal mortality increased with age. In a Norwegian study (27), plots of the log of the mortality rate against BMI categories also revealed a U-shaped association. Although it was less clear whether the BMI associated with minimal mortality increased with age, the overall curves did flatten substantially with age. However, it should be noted that Waaler (27) did not control for the effects of smoking.

More recent studies that examined the effect of age on the BMI-mortality association have controlled for smoking. In a Finnish cohort of 17 000 women followed for 12 years, there was a U-shaped BMI-all-cause mortality relation among non-smokers 25 to 64 years of age. Among women aged 65 or greater, mortality varied little according to BMI (52). Among white women from the Seventh Day Adventist cohort who never smoked, the RR of death associated with elevated BMI was lower among 55- to 74-year-olds than for 30- to 54-year-olds. For these older women, the minimal mortality was in the group with BMIs from 23 to 24.8 (53). Although the nadirs of the curves were much higher, a recent study by Seccareccia et al. (54) of over 60 000 Italian subjects again shows the increase in the nadir with age.

In one of the largest studies, Stevens et al. (34) investigated mortality over 12 years as a function of BMI across six age groups (30-44, 45-54, 55-64, 65-74, 75-84, and > 85) among 324 135 never-smokers with no apparent pre-existing disease from the American Cancer Society's Cancer Prevention Study I. Results indicated that, although greater BMI was associated with higher all-cause and CVD mortality, the RR associated with greater BMI declined somewhat with age (e.g. for men the RR of CVD mortality with an increment of 1.0 BMI units was 1.10 for 30-44-year-olds and 1.03 for 65-74-year-olds).

Bender and colleagues (55) recently examined the effect of age on excess mortality associated with obesity among 6193 obese persons enrolled in the Duseldorf Obesity Mortality Study (DOMS). When grouped into four groups based on approximate quartiles of age and BMI, it was found that the overall risk of death increased with increased body weight, but that obesity-related excess mortality declined with age at all levels of BMI.

On the whole, these studies suggest that the relative increase in rate of death associated with increased BMI is somewhat lower for older adults than for younger adults and the BMI associated with minimum mortality rate increases with age. However, as Stevens et al. (56) point out, the absolute increase in rate of death can be higher in an older than younger person even when the relative increase is lower.

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