Associations between perfluoroalkyl substances and thyroid hormones after high exposure through drinking water

BACKGROUND: The reported associations for several per- and polyfluoroalkyl substance (PFAS) with thyroid hormones are inconsistent in epidemiological studies. The purpose of the current study was to investigate the possible association of thyroid hormones in relation to serum levels of perfluorohexane sulfonate, perfluorooctane sulfonate and perfluorooctanoic acid, in a Swedish general population, highly exposed through contaminated drinking water, and if the associations with PFAS remained in a comparison to a reference group based only on residency in areas with contrasting PFAS levels.

METHOD: 3297 participants from Ronneby, a municipality with drinking water highly contaminated by PFAS (exposed group), and a reference group (N=226) from a nearby municipality with non-contaminated drinking water supply were included. Regression analysis was used to investigate the associations between PFAS exposure, assessed as exposure groups (Ronneby and reference groups) and measured serum PFAS levels, and thyroid hormone levels, with adjustments for age, sex and BMI.

RESULT: No cross-sectional associations were found between PFAS and thyroid hormones in adults and seniors except for a positive association between PFAS and fT4 in males over 50. Higher thyroid hormone levels were found in the preteen children from Ronneby compared to the reference group. In contrast, within Ronneby, there was weak evidence of associations between increased PFAS levels and decreased fT3 in preteen boys, and decreased TSH in teenage males. No such pattern was found in preteen and teenage girls.

CONCLUSION: The present study found no consistent evidence to support association of PFAS with thyroid hormones.