Early menarche is related to increased risk of breast cancer. The number of established factors that contribute to early menarche is limited. We studied prenatal and infant exposures in relation to age at menarche in a nationwide cohort of women who have a family history of breast cancer.
The study comprised 33,501 women in the Sister Study who were 35–59 years of age at baseline (2003–2009). We used polytomous logistic regression to estimate separate relative risk ratios (rRRs) and 95% confidence intervals (CIs) for associations of self-reported exposures with menarche at ≤10, 11, 14, and ≥15 years relative to menarche at 12–13 years.
Early menarche (≤10 or 11 years) was associated with having low birth weight, having had a teenage mother, being firstborn, and specific prenatal exposures: mother's smoking, diethylstilbestrol (DES), prepregnancy diabetes, and pregnancy-related hypertensive disorder. Prenatal exposures most strongly associated with very early menarche (≤10 years) were DES (rRR = 1.56 [95% CI = 1.24–1.96]), maternal prepregnancy diabetes (2.24 [1.37–3.68]), and pregnancy-related hypertensive disorder (1.45 [1.18–1.79]). Soy formula was associated with both very early menarche (1.21 [0.94–1.54]) and late menarche (14 years: 1.17 [0.98–1.40] or ≥15 years: 1.28 [1.06–1.56]).
Although menarche is only one marker of pubertal development, it is a commonly used surrogate. The observed associations of prenatal DES and soy formula exposure with age at menarche are consistent with animal data on exogenous estrogens and pubertal timing. Early-life exposures may confound associations between age at menarche and hormonally dependent outcomes in adults.
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From the aEpidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC; and bBiostatistics Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC
Submitted 7 March 2012; accepted 29 August 2012.
Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article (www.epidem.com). This content is not peer-reviewed or copy-edited; it is the sole responsibility of the author.
Supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences (Z01 ES044005).
A.A.D. is currently employed by Social & Scientific Systems, Inc. The authors report no conflict of interests.
Correspondence: Aimee D’Aloisio, Epidemiology Branch, National Institute of Environmental Health Sciences, PO Box 12233, Mail Drop A3-05, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709. E-mail: firstname.lastname@example.org.