Exposure to particulate matter air pollution and age of menarche in a nationwide cohort of US girls

Abstract

BACKGROUND AND AIM: In recent decades, age of menarche has decreased with some questioning whether environmental factors have played a role. We aimed to examine the association between exposure to particulate matter (PM) air pollution in various size fractions and time points throughout childhood and age at menarche. METHODS: Study participants were 5203 US girls in the Growing Up Today Study born between 1989 and 1995. Girls self-reported their age of menarche in three follow-up surveys (2004-2008). We examined average exposure to PM2.5, PM2.5-10, and PM10 during four windows: in utero (year prior to birth), 2 years prior to menarche, 1 year prior to menarche, and cumulative exposure from in utero to age at menarche. Air pollution measures were based on maternal address, which was updated every 2 years. Multivariable Cox proportional hazard models adjusted for race, birthweight, body size at age 5, and maternal age at menarche were used to estimate hazard ratios (HRs) and 95% CIs for the associations. RESULTS:The mean age at menarche was 12.3 years (standard deviation: 1.2). For all PM exposures, as expected, the highest average exposures were observed in utero (PM2.5: 16.1, PM2.5-10: 11.6, and PM10: 27.7 µg/m³) while the lowest were observed 1-year prior to menarche (PM2.5: 12.2, PM2.5-10: 7.2, and PM10: 19.4 µg/m³). A 5 µg/m³ increase in PM2.5 exposure was associated with earlier age at menarche during all four exposure timepoints (in utero: 1.09, 1.04-1.15; 1-year prior: 1.21, 1.14-1.29; 2-years prior: 1.23, 1.16-1.31; cumulative: 1.13, 1.06-1.20). A 5 µg/m³ increase in PM10 was associated with age at menarche during three timepoints (1-year prior: 1.05, 1.02-1.08; 2-years prior: 1.06, 1.03-1.09; cumulative: 1.03, 1.00-1.06). Exposure to PM2.5-10 was not associated with age at menarche. CONCLUSIONS:Higher exposures to PM2.5 and PM10 during childhood were associated with an earlier onset of menarche. KEYWORDS: Air pollution, Particulate matter, Reproductive outcomes