Objectives: We investigated 50-year US trends in age at menarche by socioeconomic position (SEP) and race/ethnicity because data are scant and contradictory.
Methods: We analyzed data by income and education for US-born non-Hispanic Black and White women aged 25 to 74 years in the National Health Examination Survey (NHES) I (1959-1962), National Health Examination and Nutrition Surveys (NHANES) I-III (1971-1994), and NHANES 1999-2008.
Results: In NHES I, average age at menarche among White women in the 20th (lowest) versus 80th (highest) income percentiles was 0.26 years higher (95% confidence interval [CI] = -0.09, 0.61), but by NHANES 2005-2008 it had reversed and was -0.33 years lower (95% CI = -0.54, -0.11); no socioeconomic gradients occurred among Black women. The proportion with onset at younger than 11 years increased only among women with low SEP, among Blacks and Whites (P for trend < .05), and high rates of change occurred solely among Black women (all SEP strata) and low-income White women who underwent menarche before 1960.
Conclusions: Trends in US age at menarche vary by SEP and race/ethnicity in ways that pose challenges to several leading clinical, public health, and social explanations for early age at menarche and that underscore why analyses must jointly include data on race/ethnicity and socioeconomic position. Future research is needed to explain these trends.