Obesity is defined as a body mass index (BMI) of 30 kg/m2 or higher and has been associated with early mortality. However, age-related changes in fat and lean mass that also influence health can be masked by stable BMI.
Researchers from the University of Arizona Cancer Center and Mel and Enid Zuckerman College of Public Health used data from longitudinal follow up of participants enrolled between 1993 and 1998 in the Women’s Health Initiative (postmenopausal women aged 50-79 years) to evaluate body composition and mortality risk. The study was published in the American Journal of Epidemiology.
Looking at dual-energy x-ray absorptiometry scans for estimation of total body fat (TBF) and lean body mass (LBM) from over 10,000 women who were followed for an average of 13.6 years the investigators were able to evaluate associations between BMI, body composition, and incident mortality.
Overall, BMI ≥35 was associated with increased mortality while TBF and LBM were not. An interaction between age and body composition necessitated age stratification. Among women aged 50-59 years, higher percentage of TBF increased risk of death and higher percentage LBM decreased risk of death, across a broad-range of BMIs (16.4-69.1). These relationships were reversed for women aged 70-79 years.
These data suggest the clinical utility of evaluating body composition by age group to more accurately assess mortality risk in postmenopausal women.