Determinants of age at menarche in the UK: analyses from the Breakthrough Generations Study.

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 (P(trend)<0.001), were singletons (P<0.001), had prenatal exposure to pre-eclampsia (P<0.001) or maternal smoking (P=0.01), were not breastfed (P(trend)=0.03), were non-white (P<0.001), were heavy (P(trend)<0.001) or tall (P(trend)<0.001) compared with their peers at age 7 and exercised little as a child (P(trend)<0.001). Menarcheal age increased with number of siblings (P<0.001) independently of birth order, and had an inverse association with birth order after adjustment for sibship size (P<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<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.