Background The presence of chemicals in the environment is ubiquitous. EDCs in particular may disrupt thyroid hormones, which in early life are essential for brain development. As observational studies regarding this topic are still limited, the objective of the current study was to assess the association between prenatal exposure to various EDCs and thyroxine (T4) levels in newborns in a mother-child cohort in the Netherlands.

Methods Exposure to amongst others dichlorodiphenyldichloroethylene (DDE), perfluorooctanesulfonic acid (PFOS), and perfluorooctanoic acid (PFOA) was determined in cord plasma or breast milk, and information on T4 levels in heel prick blood spots was obtained through the Dutch neonatal screening programme. Linear regression models were composed for each compound and T4. Models were stratified for gender and adjusted for a priori defined covariates.

Results Mean T4 level was 86.9 nmol/L (n = 83). Girls in Q4 of DDE and PFOA exposure showed an increased T4 level compared to Q1, a difference which remained significant in the fully adjusted model (DDE ≥ 110.01 ng/L, +22.2 nmol/L, 95% CI 1.37, 43.04; PFOA ≥ 1201 ng/L, +30.7 nmol/L, 95% CI 13.38, 48.05). In boys a lower T4 level was seen in Q2 for both PFOS and PFOA, however after adjusting the models these associations were attenuated.

Conclusion DDE, PFOS and PFOA were associated with T4 in a sex-specific manner. As the study population was relatively small, results should be considered as exploratory. More research is warranted, as studies on the role of exposure to environmental contaminants in thyroid hormone homeostasis are still limited.