Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2019 Aug 23;18(1):75.
doi: 10.1186/s12940-019-0509-z.

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

Sarah W Curtis  1 , Metrecia L Terrell  2 , Melanie H Jacobson  2 , Dawayland O Cobb  1 , Victoria S Jiang  1 , Michael F Neblett  1 , Sabrina A Gerkowicz  1 , Jessica B Spencer  1 , M Elizabeth Marder  2 , Dana Boyd Barr  2 , Karen N Conneely  3 , Alicia K Smith  4 , Michele Marcus  2
Affiliations

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

Sarah W Curtis et al. Environ Health. .

Abstract

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 (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.

Results: Higher 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.

Conclusions: This suggests that both PBB and PCB are associated with thyroid function, particularly among those who were exposed as children or prenatally.

Keywords: Age at exposure; Children’s health; DOHaD; EDC; Endocrine disrupting compound; PBB; PCB; Thyroid-stimulating hormone; Thyroxine; Triiodothyronine.

PubMed Disclaimer

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Correlation of thyroid hormone levels. The different thyroid hormone levels measured in this cohort were correlated with each other, and clustered so that the most correlated hormone levels are together (numbers are Pearson’s correlation coefficient). TSH was negatively correlated with the rest of the thyroid hormones, as expected since it is negatively regulated by them, and positively correlated with the free T3: free T4 ratio. Total and free T4 were moderately correlated, as were total and free T3. Total T4 was positively correlated with both total and free T3. Free T4 had a weak correlation with both total and free T3. The free T3: free T4 ratio is positively associated with total and free T3, but was negatively associated with total and free T4 (as expected). All correlations were statistically significant except for the association of total T3 with free T4 and TSH (p < 0.05)
Fig. 2
Fig. 2
Association of PBB exposure and thyroid hormone levels. The beta coefficients and 95% confidence interval (y-axis) for total PBB level (a) and total PCB level (b) from the regression of the five thyroid hormone levels (x-axis), also controlling for age, sex, and lipids. Free T3 (p = 0.002), free T4 (p = 0.008), and the free T3: free T4 (p = 0.0001) ratio are significantly associated with total PBB exposure. Free T4 (p = 0.0002) and the free T3: free T4 ratio (p = 0.002) are significantly associated with total PCB exposure
Fig. 3
Fig. 3
Age of exposure interacts with PBB level to predict thyroid hormone levels. There was a significant interaction between age of exposure and total PBB level in predicting total T3 (p = 0.03) (a), free T3 (p = 0.002) (b), and the free T3: free T4 ratio (p = 0.01) (c). The interaction term was not significant for predicting total T4, free T4, and TSH. The interaction term in the model was built with two continuous variables, but in order to visualize the interaction, age of exposure was dichotomized around the median and plotted with PBB level on the x-axis and hormone level on the y-axis
Fig. 4
Fig. 4
Association of PBB exposure and thyroid hormone levels stratified by exposure before or after finishing puberty. The total cohort was stratified into people who were either exposed to PBB after finishing puberty (a) or before finishing puberty (b) and the association between total PBB and all six thyroid hormone measures was tested, controlling for age, total PCB level, sex, and lipid levels. PBB and thyroid hormone levels were not associated in the subset exposed after finishing puberty, but in the subset exposed before finishing puberty, PBB and total T3 (p = 0.02), free T3 (p = 0.0003), free T4 (p = 0.02), and the free T3: free T4 ratio (p = 7.40e-5) were associated
See this image and copyright information in PMC

References

    1. Bergman A, Heindel JJ, Jobling S, Kidd KA, Zoeller RT. State of the science of endocrine disrupting chemicals: World Health Organization; 2012. Available at https://www.who.int/ceh/publications/endocrine/en/. ISBN: 978-92-807-3274-0.
    1. Porta M, Pumarega J, Gasull M, Lopez T. Contamination from endocrine disrupters of the general population at low and high concentrations. Vitam Horm. 2014;94:167–192. doi: 10.1016/B978-0-12-800095-3.00006-7. - DOI - PubMed
    1. Xue J, Liu SV, Zartarian VG, Geller AM, Schultz BD. Analysis of NHANES measured blood PCBs in the general US population and application of SHEDS model to identify key exposure factors. J Expo Sci Environ Epidemiol. 2014;24(6):615–621. doi: 10.1038/jes.2013.91. - DOI - PubMed
    1. Gore AC, Chappell VA, Fenton SE, Flaws JA, Nadal A, Prins GS, et al. EDC-2: the Endocrine Society's second scientific statement on endocrine-disrupting chemicals. Endocr Rev. 2015;36(6):E1–E150. doi: 10.1210/er.2015-1010. - DOI - PMC - PubMed
    1. De Coster S, van Larebeke N. Endocrine-disrupting chemicals: associated disorders and mechanisms of action. J Environ Public Health. 2012;2012:713696. doi: 10.1155/2012/713696. - DOI - PMC - PubMed

Publication types