Objective: Early menarche is a risk factor for breast cancer. We investigated the variation in age at menarche by socioeconomic status (SES) and race.
Methods: A cohort study was conducted on 1,091 black and 986 white girls from the three sites in the United States as part of the NHLBI Growth and Health Study (NGHS), who were aged 9-10 years at baseline and followed through adolescence over a 10-year period with annual exams. Using logistic regression models, we evaluated the nature and strength of associations between two socioeconomic indicators (household income and parental education) and early menarche (<12 years old) unadjusted and adjusted for anthropometry and maternal age at menarche.
Results: Proportionately, more black girls were menarcheal before 12 years of age compared to their white counterparts (46%, n = 468 vs. 26%, n = 240, respectively, p < 0.0001). Parental education was not a significant predictor of early menarche. The graded association between household income and age at menarche was strong and significant among black girls but less clear among white girls. Compared with those in the lowest quartile of household income, white girls in the highest quartile were at a significantly lower risk of early menarche [adjusted odds ratio (OR) = 0.37, 95% confidence intervals (CIs) 0.18-0.80]. The inverse was true for black girls: those in the highest quartile of household income were at an increased risk of early menarche (adjusted OR = 2.15, 95% CI 1.27-3.63)
Conclusion: The SES factor selected (household income versus parental education) affected the findings regarding racial differences in the timing of menarche. It will be important for future studies to elucidate the link between household income and age at menarche in developed countries.