Original Contribution Risk of Mortality According to Body Mass Index and Body Composition Among Postmenopausal Women

Obesity, often defined as a body mass index (BMI; weight (kg)/height (m)2) of 30 or higher, has been associated with mortality, but age-related body composition changes can be masked by stable BMI. A subset of Women’s Health Initiative participants (postmenopausal women aged 50–79 years) enrolled between 1993 and 1998 who had received dual-energy x-ray absorptiometry scans for estimation of total body fat (TBF) and lean body mass (LBM) (n = 10,525) were followed for 13.6 (standard deviation, 4.6) years to test associations between BMI, body composition, and incident mortality. Overall, BMI ≥35 was associated with increased mortality (adjusted hazard ratio (HR) = 1.45, 95 % confidence interval (CI): 1.16, 1.82), while TBF and LBM were not. However, an interaction between age and body composition (P < 0.001) necessitated age stratification. Among women aged 50–59 years, higher %TBF increased risk of death (HR = 2.44, 95 % CI: 1.38, 4.34) and higher %LBM decreased risk of death (HR = 0.41, 95%CI: 0.23, 0.74), despite broad-ranging BMIs (16.4–69.1). However, the relationships were reversed among women aged 70–79 years (P < 0.05). BMI did not adequately capture mortality risk in this sample of post-menopausal women. Our data suggest the clinical utility of evaluating body composition by age group to more robustly assess mortality risk among postmenopausal women. body fat; body mass index; death; lean body mass; menopaus