What Is a Healthy Body Mass Index for Women in Their Seventies? Results From the Australian Longitudinal Study on Women's Health

Background. This study examines the relevance of the World Health Organization (WHO) optimal range for body mass index (BMI) of 18.5-25 kg/m(2) to morbidity in older women. Methods. Data were from 11,553 women who completed five mailed surveys at 3-year intervals between 1996 (age 70-75 years) and 2008 (age 82-87 years). Incidence and prevalence of diabetes mellitus (DM), hypertension, heart disease, and osteoporosis; hospital admissions; and mortality were assessed. The association between BMI in 1996 and each outcome was examined using logistic regression models with repeated measures and a proportional hazards model for survival. Results. There were consistent associations between increasing BMI and increasing incidence and prevalence of DM, hypertension, and heart disease and between increasing BMI and decreasing risk of osteoporosis. The association with hospital admission was J shaped and lowest for BMI of 22-24 kg/m(2), whereas the association with mortality was U shaped, being lowest for BMI of 25-27 kg/m(2). These associations were not affected by excluding women with cancer or excluding the first 5 years of follow-up. Conclusions. These results illustrate the complexity of determining the optimal BMI range for women who survived to age 70-75 years. Although the WHO recommendation is appropriate for DM, hypertension, heart disease, and hospitalization, a slightly higher BMI range may be optimal for osteoporosis and mortality.