The Relationship between Perfluoroalkyl Substances Concentrations and Thyroid Function in Early Childhood: A Prospective Cohort Study

BACKGROUND: Exposure to perfluoroalkyl substances (PFAS) has been suggested to affect thyroid function; however, data on early-life exposure and thyroid function in early childhood are scarce. We investigated the cross-sectional and longitudinal relationships of early-life exposure to PFAS with thyroid function at 2, 4, and 6 years of age.

METHODS: This study used data on PFAS exposure and thyroid function from the Environment and Development of Children (EDC) cohort study. A total of 660 children who visited at least once at 2, 4, or 6 years of age (381 children aged 2 years, 569 children aged 4 years, and 511 children aged 6 years) were included in this study. Serum thyroid-stimulating hormone (TSH) levels were measured at 2, 4, and 6 years of age. The relationship of serum PFAS concentrations (sPFAS) with TSH levels at the 3 time points was assessed by repeated-measure analysis using linear mixed models. The serum levels of free thyroxine (FT4) and triiodothyronine (T3) were measured once (at 6 years of age). The relationship of sPFAS with FT4 and T3 levels at 6 years of age was investigated by linear regression analyses.

RESULTS: None complained of hyper- or hypothyroid symptoms with normal FT4 and T3 levels. Repeated-measure analysis showed that TSH levels at ages 2, 4, and 6 years of age were inversely associated with sPFNA, after adjusting for age, sex, and/or dietary iodine intake (p<0.05). When stratified by sex, TSH levels were inversely associated with sPFOA in boys and sPFNA in girls (p<0.05 for both). FT4 levels at 6 years of age were positively related to sPFNA and sPFHxS at 2 years of age and sPFOA at 6 years of age, and T3 levels at 6 years of age showed positive relationships with sPFDA and sPFOS at 6 years of age (p<0.05 for all). When stratified by sex, similar positive relationships for sPFAS with FT4 and T3 levels were significant among boys only.

CONCLUSIONS: A significant relationship was found between early-life exposure to PFAS and thyroid function. Early-life exposure to PFAS was associated with decreased TSH and increased FT4 or T3 levels among preschool-age children.