Abstract
Background: Metals may disrupt thyroid hormones (TH) like thyroid stimulating hormone (TSH), thyroxine (T4) and triiodothyronine (T3). We examined whether hair (MnH) and blood manganese (MnB), and blood lead (PbB) concentrations explained serum TH concentrations in pregnant women from the ISA birth cohort in Costa Rica.Methods: Using the first sample of each women (n=384), we ran separate multivariate linear regression models and General Additive Models (GAMs) adjusting for gestational age, maternal age, cotinine, prepregnancy Body Mass Index and severe vomiting. We also ran stratified analysis by trimester of pregnancy.Results: Median (p25-75) TSH, FT3, FT4 concentrations were: 1.47 (1.06-2.08) mIU/L, 4.60 (4.29-5.06) pmol/L, and 14.09 (13.00-15.65) pmol/L, respectively. Median (p25-75) MnH, MnB and PnB were 1.62 (0.86-3.49) μg/g, 23.44 (19.36-27.43), 6.66 (5.17-9.08) μg/L, respectively. Increased MnH was associated with increased TSH (% of change = 13,24, 95%CI -1,95, 30,79 for each 1% increase in MnH) during the second trimester of pregnancy. In addition, MnH showed a non-linear association with FT4 during the third trimester of pregnancy (GAM estimated degrees of freedom >2 with p<0.05). Overall, higher MnB concentrations were associated with increased FT4, ß=0,04 (95%CI 0, 0,07). Associations were strongest during the first trimester ß=0,13 95% CI: 0,05, 0,21). MnB also showed a non-linear association with FT3 during the first trimester. Finally, increased PbB concentrations were associated with higher FT4 [β=0.07 (95% CI: 0.00, 0.13)], particularly during the second trimester of pregnancy [β=0.10 (95% CI: 0.02, 0.19)]Conclusion: Our findings show that both manganese and lead explain TH concentrations during pregnancy. For Mn, being an essential element, this may reflect normal physiological functioning. Nevertheless, increased MnH is likely to reflect excess Mn and associations may also reflect endocrine disrupting effects. For lead, results show even very low concentrations might affect TH and possibly cause endocrine disrupting effects.
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