Organochlorine compounds, iodine intake, and thyroid hormone levels during pregnancy

The effect of organochlorine compounds (OCs) on thyroid function, as well as the potential confounding effect of iodine intake, was studied in a large sample of pregnant women from two population-based cohort studies in Sabadell (n = 520) and Gipuzkoa (n = 570), Spain. Thyroid hormones (free T4 and total T3), thyrotropin, and polychlorinated biphenyls (PCB congeners 118, 138, 153, and 180), hexachlorobenzene (HCB), beta-hexachlorocyclohexane (beta-HCH), dichlorodiphenyl dichloroethylene (p'p'-DDE) and dichlorodiphenyl richloroethane (p'p-DDT) were measured in serum samples collected at first trimester of pregnancy. Urinary iodine concentration (UIC) was measured and iodine intake from diet, iodized salt, and supplements were estimated from a food frequency questionnaire. Levels of HCB and PCBs congeners 180, 153, and 138 were related to lowe rtotal T3 levels (adjusted coefficient (SE): -4.0(1.1), -6.1(1.6), -5.5(1.6), and 3.8(1.4), respectively) and higher free T4 levels (adjusted coefficient (SE): 0.013(0.05), 0.017(0.007), 0.016(0.007), and 0.007(0.006), respectively). These associations were homogeneous in both cohorts, especially for PCBs and total T3 (p-value forthe interaction between cohorts >0.8). Iodine intake and UIC did not affect the association between OCs and thyroid hormones. Our results indicate that exposure to OCs during pregnancy can alter TH levels.