Early Life Exposure To Phthalate Diesters: Associations With Thyroid Function And Cognitive Function

Abstract

Background: Epidemiological studies concerning the relations of exposure to phthalates, thyroid function and cognitive function among children could be limited. Objectives: We conducted the longitudinal study to examine the associations of prenatal and postnatal exposure to phthalates, thyroid function and cognitive function in children 2-9 years old. Methods: We recruited 430 pregnant women in their trimester in Taichung, Taiwan from 2001-2002. A total of 110, 79, and 76 children were followed up at ages 2, 5, and 8, respectively. The serum levels of thyroxine (T4), unbound T4 (FT4), triiodothyronine (T3), thyroid-stimulating hormone (TSH), and thyroxine-binding globulin (TBG) in children were measured at three different time points using radioimmunoassay. We also evaluated the children's cognitive function at three followed-up visits using the Bayley and Wechsler tests for assessing neurocognitive function and intelligence (IQ). Urine samples from mothers during pregnancy and from children at each follow-ep visit were analyzed for seven metabolite concentrations of widely used phthalate esters (such as MMP, MEP, MBP, MBzP, MEHP, MEHHP, and MEOHP). We constructed a linear mixed model to examine these associations after adjusted for covariates. Results: We found significant inverse associations between the children's levels of urinary MEHHP, MEOHP, and the sum of the three metabolites of di(2-ethylhexyl) and their serum levels of FT4 (i.e. Beta= -0.04, 95% CI: -0.07, -0.01 for MEOHP). Urinary MMP, MEP, MBP, MBzP, MEHP, and MEOHP levels in children were significantly negatively related to IQ scores (i.e. Beta= -1.85, 95% CI: -3.40, -0.30 for MEOHP). We found a marginally significant positive relationship between the children's serum levels of FT4 and their IQ scores (Beta=5.81, 95% CI: -2.74, 14.36 for MEOHP). Conclusions: Early life exposure to phthalate diesters could be associated with decreasing thyroid function and cognitive development in the young children.