Determinants of age at menarche in the United Kingdom: analyses from the Breakthrough Generations Study
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Background: Early menarche increases breast cancer risk but, aside from weight, information on its determinants is limited. Methods: Age at menarche data were collected retrospectively by questionnaire from 81 606 women aged 16–98, resident in the UK and participating in the Breakthrough Generations Study. Results: Menarche occurred earlier in women who had a low birthweight (Ptrend\ensuremath<0.001), were singletons (P\ensuremath<0.001), had prenatal exposure to pre-eclampsia (P\ensuremath<0.001) or maternal smoking (P=0.01), were not breastfed (Ptrend=0.03), were non-white (P\ensuremath<0.001), were heavy (Ptrend\ensuremath<0.001) or tall (Ptrend\ensuremath<0.001) compared with their peers at age 7 and exercised little as a child (Ptrend\ensuremath<0.001). Menarcheal age increased with number of siblings (P\ensuremath<0.001) independently of birth order, and had an inverse association with birth order after adjustment for sibship size (P\ensuremath<0.001). In a multivariate model, birthweight, ethnicity, weight, height, exercise, sibship size and birth order remained significant, and maternal age at birth became significant (positive association, P\ensuremath<0.001). Conclusion: Age at menarche was influenced by both pre- and post-natal factors, and these factors may affect breast cancer risk through this route.
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BRITISH JOURNAL OF CANCER, 2010