BACKGROUND:: Phthalates are hypothesized to cause obesity, but few studies have assessed whether prenatal phthalate exposures are related to childhood body mass index (BMI). METHODS:: We included 707 children from three prospective cohort studies enrolled in the United States between 1998 and 2006 who had maternal urinary phthalate metabolite concentrations measured during pregnancy, and measures of weight and height at ages 4 to 7 years. We calculated age- and sex-standardized BMI z-scores and classified children with BMI percentiles ≥85 as overweight/obese. We used mixed effects regression models to estimate associations between a 1-standard deviation increase in natural log phthalate metabolite concentrations and BMI zscores and overweight/obesity. We estimated associations in multiple metabolite models adjusted for confounders, and evaluated heterogeneity of associations by child’s sex, race/ethnicity, and cohort RESULTS:: Mono-3-carboxypropyl phthalate (MCPP) concentrations were positively associated with overweight/obese status in children (odds ratio [95% credible interval] = 2.1 [1.2, 4.0]) but not with BMI z-scores (beta = -0.02 [-0.15, 0.11]). We did not observe evidence of obesogenic effects for other metabolites. However, monoethyl phthalate (MEP) and summed di-(2-ethylhexyl) phthalate metabolites (∑DEHP) concentrations were inversely associated with BMI z-scores among girls (MEP beta = -0.14 [-0.28, 0.00]; ∑DEHP beta = -0.12 [-0.27, 0.02]). CONCLUSIONS:: Maternal urinary MCPP, a non-specific metabolite of several phthalates, was positively associated with childhood overweight/obesity. Metabolites of diethyl phthalate and DEHP were associated with lower BMI in girls but not boys, suggesting prenatal exposures may have sexually dimorphic effects on physical development.
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