Abstract
BackgroundMichigan 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.MethodsLinear regression models were used to test the association between serum measures of thyroid function (total thyroxine (T4), total triiodothyronine (T3), free T4, free T3, thyroid stimulating hormone (TSH), and free T3: free T4 ratio) and serum PBB and PCB levels in a cross-sectional analysis of 715 participants in the Michigan PBB Registry.ResultsHigher PBB levels were associated with many thyroid hormones measures, including higher free T3 (p = 0.002), lower free T4 (p = 0.01), and higher free T3: free T4 ratio (p = 0.0001). Higher PCB levels were associated with higher free T4 (p = 0.0002), and higher free T3: free T4 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 T3 (p = 0.01) and free T3 (p = 0.0003), lower free T4 (p = 0.04), and higher free T3: free T4 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.ConclusionsThis suggests that both PBB and PCB are associated with thyroid function, particularly among those who were exposed as children or prenatally.
Highlights
Michigan residents were directly exposed to endocrine-disrupting compounds, polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB)
In 1973, millions of Michigan residents were exposed to polybrominated biphenyl (PBB), a brominated flame retardant and an Endocrine-disrupting compound (EDC), when a factory accident caused it to be added to the food supply [7, 8]
The Michigan PBB Registry was originally started after the agricultural accident by the Michigan Department of Community Health (MDCH), and recruited individuals believed to have the highest exposure to PBB: people living on quarantined farms, people who ate food from quarantined farms, and chemical workers and their families
Summary
Michigan residents were directly exposed to endocrine-disrupting compounds, polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB). The people who were believed to have the highest direct exposure – people living on or obtaining food from quarantined farms and the Michigan Chemical Company’s workers and their families – were recruited to investigate the long-term health effects of PBB exposure These participants, their children, and other members of the community have been followed for the past 40 years as part of the Michigan PBB Registry and have had their current serum levels of PBB regularly assessed, as well as their exposure to the structurally-related polychlorinated biphenyl (PCB), which they were continuously exposed to from typical environmental sources [7,8,9]
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