Does early life phthalate exposure mediate racial disparities in children's cognitive abilities?

Early life exposure to phthalates may be associated with reduced cognition. However, it is unknown if disproportionate exposure to phthalates contributes to racial disparities in children's intellectual abilities.

We used data from 253 mother-child pairs in Cincinnati, OH (the Health Outcomes and Measures of the Environment study, 2003-2006). We measured urinary concentrations of 11 phthalate metabolites twice during pregnancy and up to six times in childhood. We evaluated children's cognitive abilities at ages 5 and 8 years. Using mediation models, we quantified covariate-adjusted direct and indirect effects of race on children's Full-Scale Intelligence Quotient (IQ) scores for individual phthalate metabolite concentrations during gestation and childhood.

Average IQ scores among Black children (n = 90) were 7.0 points lower (95% confidence interval [CI] = -12, -1.8) than among White children (n = 145) after adjustment for socioeconomic factors. Urinary monobenzyl phthalate and monoethyl phthalate (MEP) concentrations during gestation and childhood were higher among Black than White children. We did not observe evidence that phthalate concentrations mediated the race-IQ association, with the exception of MEP. Childhood MEP concentrations partially mediated the race-IQ association. For instance, each 10-fold increase in MEP concentrations at age 2 years contributed to a 1.9-point disparity in IQ scores between Black and White children (95% CI = -4.7, 0.7). Other phthalate metabolite concentrations during pregnancy or childhood did not mediate the race-IQ association.

Despite observing racial disparities in exposure to some phthalates and IQ, we found little evidence that phthalates contribute to IQ disparities.