Abstract
OBJECTIVE: Studies have shown that earlier age at menarche is associated with a higher risk of midlife obesity; however, the mechanism underlying this association is not known. The purpose of this study was to examine whether the association between age at menarche and midlife obesity is due to variation in circulating androgen concentrations. METHODS: Baseline data were analyzed from 748 women aged 45 to 54 years enrolled in the Midlife Women's Health Study, a prospective cohort study conducted in the Baltimore, MD region. Information on age at menarche was collected through a self-administered questionnaire. Body mass index (BMI) was calculated using height and weight measured at a clinic visit. Obesity was defined as a BMI between 30 and 34.9 kg/m; super obesity was defined as a BMI greater than 35 kg/m. Testosterone, estradiol, and sex hormone-binding globulin were measured in blood samples using enzyme-linked immunosorbent assays. The free androgen index (FAI) was calculated using the formula: (testosterone × 3.467)/sex hormone-binding globulin × 100. RESULTS: After adjustment for covariates, for each year increase in age at menarche, the odds of obesity and super obesity decreased by 31% (odds ratio (OR) 0.69; 95% confidence limits (CL) 0.59, 0.81) and 34% (OR 0.66; 95% CL 0.52, 0.83), respectively. Addition of the FAI into the models did not attenuate the observed estimates. CONCLUSIONS: The results of this study indicate that age at menarche is associated with midlife obesity independent of free testosterone concentrations measured in adulthood.