17-beta-estradiol in relation to age at menarche and adult obesity in premenopausal women.

BACKGROUND We hypothesize that premenopausal endogenous estradiol may be associated with age at menarche and adult overweight and obesity, potentially contributing to breast cancer risk. METHODS We assessed age at menarche by questionnaire among 204 healthy Norwegian women, aged 25-35 years. Measures of body composition included body mass index (BMI, kg/m(2)), waist circumference (WC, cm), waist-to-hip ratio (WHR) and fat percentage dual energy X-ray absorptiometry, (DEXA). Daily salivary 17-beta-estradiol (E(2)) concentrations were collected throughout one entire menstrual cycle and assessed by radioimmunoassay (RIA). Linear regression analyses and linear mixed models for repeated measures were used and potential confounding factors and effect modifiers were tested. RESULTS Among women with an early age at menarche (< or =12 years), the overall mean salivary E(2) concentration increased by 3.7 pmol/l (95% confidence interval, 1.8-5.7 pmol/l) with each 9.8 cm (1 SD) increase in WC, which represents a 20.7% change in the mean for the total group. Among the same early maturers, a 1 SD (0.06) change in WHR was directly associated with a 24.0% change in mean E(2) concentration for the total group. CONCLUSIONS Our findings support the hypothesis that early age at menarche, together with adult overweight and obesity, result in high levels of 17-beta-estradiol throughout the menstrual cycle.