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

BACKGROUND: We hypothesize that premenopausal endogenous estradiol may beassociated 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 healthyNorwegian women, aged 25–35 years. Measures of body compositionincluded body mass index (BMI, kg/m²), waist circumference (WC,cm), waist-to-hip ratio (WHR) and fat percentage dual energyX-ray absorptiometry, (DEXA). Daily salivary 17-β-estradiol(E₂) concentrations were collected throughout one entire menstrualcycle and assessed by radioimmunoassay (RIA). Linear regressionanalyses and linear mixed models for repeated measures wereused and potential confounding factors and effect modifierswere tested. RESULTS: Among women with an early age at menarche (12 years), the overallmean salivary E₂ 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 themean for the total group. Among the same early maturers, a 1SD (0.06) change in WHR was directly associated with a 24.0%change in mean E₂ 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 levelsof 17-β-estradiol throughout the menstrual cycle.