Blood Lead Concentration in Childhood and Age of Menarche in a Prospective Study of U.S. Girls

摘要

Lead may alter growth and development, but prospective studies on menarche are lacking. Among girls enrolled at 6-8 years of age in the Breast Cancer and Environment Research Program cohort during 2004-2007 and followed up to 11 years, lead in blood (PbB) was measured in a single sample, primarily before menarche but up to 7 years after. Median PbB was 0.95 μg/dL (IQR 0.69-1.3) and age of menarche 12.2 years (IQR 11.2-13; n=809). Associations of In(PbB) with menarcheal age were estimated using Cox proportional hazards models adjusted for age and height at PbB sample collection and race/ethnicity. Associations were null in unadjusted models. Adjusted associations were also null among all girls or those whose PbB sample was obtained 2-9 years before menarche (n=654, aHR 1.02 95%CI 0.86 - 1.22). If PbB was measured within 1 year of menarche or after, the association was inverse (n=155, aHR 0.64, CI 0.43-0.96). The latter finding closely resembles those of prior cross-sectional studies and may arise because PbB concentrations decline during childhood when PbB is diluted by body size during maximal growth. The group of 155 girls with PbB obtained near or after menarche differed significantly from the 654 followed prospectively, with older median age at sampling of 11 vs. 8 years old, lower PbB: 0.76 vs. 0.99 μg/dL, taller height: 60 vs. 50 in; and earlier menarcheal age: 11.1 vs. 12.4 years, respectively. Therefore, cross-sectional studies reporting associations of PbB with delayed menarche may not have adequately adjusted for rapid growth or measured PbB in an appropriate susceptibility window. During childhood, intercorrelations among PbB, height, age, and menarche can seriously confound associations. In our longitudinal analysis with prepubertal PbB measures there was no association with age of menarche. These findings and conclusions have not been disseminated by the Centers for Disease Control and Prevention and do not represent any agency determination or policy.