Body Mass Index, Waist Circumference, and Mortality in a Large Multiethnic Postmenopausal Cohort-Results from the Women's Health Initiative.

OBJECTIVES: To determine whether the relationship between anthropometric measurements of obesity and mortality varies according to age, race, and ethnicity in older women.

DESIGN: Prospective cohort study of multiethnic postmenopausal women.

SETTING: Women's Health Initiative (WHI) observational study and clinical trials in 40 clinics.

PARTICIPANTS: Postmenopausal women aged 50-79 participating in WHI (N = 161,808).

MEASUREMENTS: Baseline height, weight, and waist circumference (WC) were measured, and body mass index (BMI) was calculated based on height and weight. Demographic, health, and lifestyle data from a baseline questionnaire were used as covariates. The outcome was adjudicated death (n = 18,320) during a mean follow-up of 11.4 ± 3.2 years.

RESULTS: Hazard ratios (HRs) and 95% confidence intervals (95% CIs) indicated that ethnicity and age modified (P < .01) the relationship between obesity and mortality. Underweight was associated with higher mortality, but overweight or slight obesity was not a risk factor for mortality in most ethnic groups except for Hispanic women in the obesity I category (HR = 1.42, 95% CI = 1.04-1.95). BMI was not or was only weakly associated with mortality in individuals aged 70-79 (HR = 0.90, 95% CI = 0.85-0.95 for overweight; HR = 0.98, 95 CI = 0.92-1.06 for obese I; HR = 1.11, 95% CI = 1.00-1.23 for obese II; HR = 1.08, 95% CI = 0.92-1.26 for obese III). In contrast, higher central obesity measured using WC was consistently associated with higher mortality in all groups.

CONCLUSION: Underweight is a significant risk factor for mortality in older women, and healthy BMI ranges may need to be specific for age, race, and ethnicity. The findings support a consistent relationship between central obesity and mortality.