Thyroid hormones in relation to toxic metal exposure in pregnancy, and potential interactions with iodine and selenium
Journal article, 2021
Several endocrine-disrupting metals may affect thyroid function, but the few available studies of exposure during pregnancy and thyroid hormones are inconclusive. Objective: To explore if environmental exposure to cadmium (Cd), lead (Pb), and methylmercury (MeHg) impacts thyroid function in pregnancy, and interacts with iodine and selenium status.
Methods:
Women in a Swedish birth cohort provided blood and urine samples in early third trimester. Concentrations of erythrocyte Cd, Pb, and Hg (n = 544), urinary Cd and iodine (n = 542) and plasma selenium (n = 548) were measured using inductively coupled plasma-mass spectrometry. Free and total thyroxine (fT4, tT4) and triiodothyronine (fT3, tT3), and thyroid stimulating hormone (TSH), were measured in plasma (n = 548) with electrochemiluminescence immunoassays. Metal-hormone associations were assessed in regression models, and metal mixture effects and metal-nutrient interactions were explored in Bayesian kernel machine regression (BKMR).
Results:
In multivariable-adjusted regression models, a doubling of urinary Cd was associated with a mean increase in tT4 of 2.7 nmol/L (95% CI: 0.78, 4.6), and in fT3 and tT3 of 0.06 pmol/L (0.02, 0.10) and 0.09 nmol/L (0.05, 0.13), respectively. A doubling of urinary Cd was associated with a −0.002 (−0.003, −0.001) and −0.03 (−0.05, −0.02) decrease in the fT4:tT4 and fT3:tT3 ratio, respectively. A doubling of erythrocyte Hg (>1 µg/kg) was associated with a decrease in fT3 and tT3 by −0.11 pmol/L (−0.16, −0.05) and −0.11 nmol/L (−0.16, −0.06), respectively, and a −0.013 (−0.02, −0.01) decrease in the fT3:fT4 ratio. BKMR did not indicate any mixture effect of toxic metals or interactions between metals and iodine or selenium in relation to the hormones.
Conclusion:
Our findings suggest that exposure to Cd and Hg, at levels globally prevalent through the diet, may affect thyroid function during pregnancy, independently of iodine and selenium levels. Further studies on potential implications for maternal and child health are warranted.
Thyroxine
Thyroid stimulating hormone
Pregnancy
Toxic metals
Triiodothyronine
Essential elements
Author
Klara Gustin
Karolinska Institutet
Malin Barman
Karolinska Institutet
Chalmers, Biology and Biological Engineering, Food and Nutrition Science
Helena Skröder
Karolinska Institutet
Bo Jacobsson
Sahlgrenska University Hospital
Norwegian Institute of Public Health
University of Gothenburg
Anna Sandin
Umeå University
Ann-Sofie Sandberg
Chalmers, Biology and Biological Engineering, Food and Nutrition Science
Agnes E Wold
University of Gothenburg
Marie Vahter
Karolinska Institutet
Maria Kippler
Karolinska Institutet
Environment International
0160-4120 (ISSN) 1873-6750 (eISSN)
Vol. 157 106869Subject Categories
Environmental Health and Occupational Health
Public Health, Global Health, Social Medicine and Epidemiology
Obstetrics, Gynecology and Reproductive Medicine
DOI
10.1016/j.envint.2021.106869
PubMed
34530290