Thyroid hormone levels associate with exposure to polychlorinated biphenyls and polybrominated biphenyls in adults exposed as children

BACKGROUND: Michigan residents were directly exposed to endocrine-disrupting compounds, polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB). A growing body of evidence suggests that exposure to certain endocrine-disrupting compounds may affect thyroid function, especially in people exposed as children, but there are conflicting observations. In this study, we extend previous work by examining age of exposure’s effect on the relationship between PBB exposure and thyroid function in a large group of individuals exposed to PBB. METHODS: Linear regression models were used to test the association between serum measures of thyroid function (total thyroxine (T(4)), total triiodothyronine (T(3)), free T(4), free T(3), thyroid stimulating hormone (TSH), and free T(3): free T(4) ratio) and serum PBB and PCB levels in a cross-sectional analysis of 715 participants in the Michigan PBB Registry. RESULTS: Higher PBB levels were associated with many thyroid hormones measures, including higher free T(3) (p = 0.002), lower free T(4) (p = 0.01), and higher free T(3): free T(4) ratio (p = 0.0001). Higher PCB levels were associated with higher free T(4) (p = 0.0002), and higher free T(3): free T(4) ratio (p = 0.002). Importantly, the association between PBB and thyroid hormones was dependent on age at exposure. Among people exposed before age 16 (N = 446), higher PBB exposure was associated with higher total T(3) (p = 0.01) and free T(3) (p = 0.0003), lower free T(4) (p = 0.04), and higher free T(3): free T(4) ratio (p = 0.0001). No significant associations were found among participants who were exposed after age 16. No significant associations were found between TSH and PBB or PCB in any of the analyses conducted. CONCLUSIONS: This suggests that both PBB and PCB are associated with thyroid function, particularly among those who were exposed as children or prenatally. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12940-019-0509-z) contains supplementary material, which is available to authorized users.