摘要：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. Age at menarche is of clinical, public health, and social importance, 1–4 but in the United States scant and contradictory data exist as to whether trends in the overall declining age at menarche 1,2 vary by race/ethnicity and socioeconomic position (SEP), singly and combined. 5–9 Highlighting the biological relevance of age at menarche, evidence indicates age at menarche is influenced by nutrition from gestation through childhood, which is germane to girls’ risk of becoming pregnant and predictive of chronic disease, for example, early age associated with increased risk for breast cancer and cardiovascular disease. 1–3 Socially, age at menarche matters for both girls’ sense of themselves and how they are treated by others, with early maturation increasing the likelihood of girls being precociously sexualized and sexually harassed. 3,4 Factors hypothesized to affect age at menarche range from material (e.g., impact of economic deprivation on nutrition) to psychosocial (e.g., association between childhood sexual abuse and earlier age of onset). 1,2,5 Consistent with trends in improved nutrition, robust evidence indicates that age at menarche has overall declined since the early 20th century in North America and Europe. 1,2,5 European and Latin American studies likewise indicate that lower age at menarche, once more common among affluent girls, has become more common among more impoverished girls, with the decline in age fastest among impoverished girls. 1,10–13 In the United States, however, although some studies have reported that age at menarche and its decline are higher and faster among Black than among White girls (consistent with higher rates of poverty among the Black than among the White population), other studies have reported the reverse. 6–9 No US studies have analyzed US socioeconomic trends in age at menarche overall or by race/ethnicity. To address gaps and inconsistencies in evidence, we have presented novel data on 50-year social patterns and trends in age at menarche among US-born non-Hispanic Black and White women, stratified by SEP. Additionally, we have employed a metric developed in evolutionary biology—the haldane 14–16 —which scales the pace of change in population traits (phenotypic or genotypic) to biological generation, rather than calendar year, and which, although rarely used in human health research, provides a benchmark for gauging the tempo of change within and across humans and other species. 14
