摘要：Objectives. We examined the relation between measures of body size and mortality in a predominantly White cohort of 8029 women aged 65 years and older who were participating in the Study of Osteoporotic Fractures. Methods. Body composition measures (fat and lean mass and percentage body fat) were calculated by bioelectrical impedance analysis. Anthropometric measures were body mass index (BMI; kg/m2) and waist circumference. Results. During 8 years of follow-up, there were 945 deaths. Mortality was lowest among women in the middle of the distribution of each body size measure. For BMI, the lowest mortality rates were in the range 24.6 to 29.8 kg/m2. The U-shaped relations were seen throughout the age ranges included in this study and were not attributable to smoking or measures of preexisting illness. Body composition measures were not better predictors of mortality than BMI or waist girth. Conclusions. Our results do not support applying the National Institutes of Health categorization of BMI from 25 to 29.9 kg/m2 as overweight in older women, because women with BMIs in this range had the lowest mortality. More than 50% of the US adult population is overweight or obese according to the criteria of the National Heart, Lung, and Blood Institute (NHLBI). 1 The NHLBI expert panel defined overweight as body mass index (BMI; weight in kilograms divided by height in meters squared) from 25.0 to 29.9 kg/m2 and obesity as BMI≥ 30.0 kg/m2. 1 However, applying a single set of cutpoints to define overweight and obesity in different age groups may not be appropriate. Several studies have suggested that the relative risk of mortality associated with increased BMI is greater among younger women than older women. 2 – 7 The shape of the relation between BMI and mortality is also controversial. One large prospective study showed a positive linear association between BMI and mortality in women aged 30 to 55 years who had been followed for 16 years 8 ; several other studies of women at various ages have reported a U-shaped relation, 2 , 5 , 9 – 18 which indicates an elevated mortality risk among those with low BMI and those with high BMI. Some evidence suggests that this nonlinear association may be the result of not controlling for confounding by smoking or preexisting illness, 19 but other studies have observed a U-shaped distribution even when adjusting for these variables. 5 , 9 , 10 , 12 – 16 We used data from the Study of Osteoporotic Fractures, a large prospective cohort study of predominantly White women aged 65 years and older, to examine the relation between measures of obesity and mortality during an 8-year-average follow-up period. Body composition was measured directly by bioelectrical impedance analysis (BIA) as well as by traditional measures of adiposity, including BMI and waist circumference.
