Early exposure to perfluoroalkyl substances (PFAS) affects thyroid function in preschool-aged children, according to the results of a prospective cohort study published in Thyroid.
Accumulation of PFAS in the body is associated with disrupted thyroid hormone homeostasis. Childhood represents a time of rapid growth and development and vulnerability to endocrine-disrupting chemicals, however the early-life effects of PFAS exposure on thyroid function remain unclear.
Using data from the Environment and Development of Children (EDC) study, investigators aimed to evaluate the relationship between serum PFAS levels in a Korean pediatric cohort on current and subsequent thyroid function in early childhood.
Serum thyrotropin (TSH) levels were measured at 2, 4, and 6 years of age. Free thyroxine (FT4) and total triiodothyronine (T3) levels were measured at 6 years of age for all children and at age 2 and 4 years for children with abnormal TSH levels. Serum concentrations of 14 PFAS species were measured using liquid chromatography tandem-mass spectrometry.
A total of 660 children (47.3% girls) were included in the analysis. Serum levels of 5 PFAS species were present in >90% of children at all ages, including 4 which were detected in >95% of children (perfluorooctane sulfonic acid [PFOS], perfluorooctanoic acid [PFOA], perfluorohexane sulfonic acid [PFHxS], and perfluorononanoic acid [PFNA]). Serum PFOS levels were significantly higher in boys (4.399±1.761 ng/mL) than in girls at 6 years of age (4.015±1.603 ng/mL; P =.038).
No children complained of hyperthyroid or hypothyroid symptoms, but TSH levels were elevated in 5.0% and 4.7% of children at 2 and 4 years of age, respectively. Low TSH levels were observed in only 1 patient at 2 years of age. FT4 and T3 levels were within reference ranges at all ages.
Subclinical hyperthyroidism and hypothyroidism were identified in 1 boy and 24 children, respectively. Serum levels of PFHxS (adjusted odds ratio, 0.34; 95% CI, 0.13-0.85) and PFOS (adjusted odds ratio, 0.37; 95% CI, 0.14-0.97) were significantly associated with subclinical hypothyroidism at 6 years of age (P <.05 for both).
After adjusting for age and sex, TSH levels were inversely associated with serum PFAS levels. This relationship was significant for serum PFNA levels (effect size, -0.053; P =.014). When stratified by sex, TSH levels were inversely associated with serum PFOA levels in boys and PFNA levels in girls (P <.05 for both). This relationship remained significant in girls after adjusting for iodine intake (P =.026).
FT4 levels were positively associated with serum PFNA and PFHxS levels at 2 years of age and PFOA levels at age 6 years after adjusting for age, sex, and iodine intake (P <.05 for all). At age 6 years, T3 levels were positively associated with serum PFOS and perfluorodecanoic acid (P <.05 for both). When stratified by sex, similar associations were observed, which were significant only in boys.
The researchers noted that the measurement of FT4 and T3 levels at 6 years of age only represented a limitation of the study.
“PFAS were significantly associated with decreased TSH and increased FT4 or T3 levels,” the study authors concluded. “Whether this effect of PFAS on thyroid function in preschool-age children is sustained in school-age children or whether it gives rise to other health problems in childhood and adolescence needs to be further evaluated.”
Kim HY, Kim K-N, Shin CH, et al. The relationship between perfluoroalkyl substances concentrations and thyroid function in early childhood: a prospective cohort study [published online May 5, 2020]. Thyroid. doi:10.1089/thy.2019.0436