Incidence of Thyroid Disease Following Exposure to Polybrominated Biphenyls and Polychlorinated Biphenyls, Michigan, 1974–2006

Abstract

O-29B4-2 Background/Aims: Although the thyroid gland plays a crucial metabolic role throughout life, the effects of persistent chemicals on the thyroid have received limited attention. Of particular interest are persistent organic pollutants, which are used in many consumer products and are increasing in environmental concentration. Our objective was to examine the relationship between serum polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB) concentrations and thyroid disease incidence. Methods: We employed incidence density sampling to perform a nested case control analysis of the Michigan Long-term PBB Cohort. Cohort members (n = 3333) were exposed to PBBs following the unintentional 1973 contamination of cattle feed and to PCBs through diet and the environment. Serum PBB and PCB concentrations were measured at enrollment; cases were cohort members who answered “Yes” to “Has a healthcare provider ever told you that you had a thyroid problem?” during follow-up interviews. We calculated odds ratios (OR) with 95% confidence intervals (CI) and assessed body mass index (BMI), smoking, and prior pregnancy for confounding and effect modification. Results: Total cumulative thyroid disease incidence after 33 years was 13.9% among females and 2.6% among males. After adjusting for BMI, there were no statistically significant differences in thyroid disease incidence by PBB or PCB exposure among females. There was a trend towards increased thyroid disease incidence among males exposed to PBBs or PCBs, but this was statistically insignificant. Compared to controls, women with a thyroid disease had increased odds of being overweight/obese (OR = 2.82; 95% CI: 1.94, 4.11) and having infertility (OR = 1.71; 95% CI: 1.08, 2.69), diabetes (OR = 1.61; 95% CI: 1.04, 2.51), or arthritis (OR = 1.71; 95% CI: 1.18, 2.50). Conclusion: The Michigan Long-term PBB Cohort is and will continue to be valuable in assessing the public health impacts of PBB and PCB exposures. Additional research is warranted to further explore potential associations between PBBs/PCBs and adverse thyroid disease in males.