Understanding the Relationship Between Selenium, Iodine and Associated Biomarkers During Pregnancy and The Effect on Birth Weight

Selenium and iodine are essential dietary trace elements required for oxidative protection and thyroid hormone metabolism. Iodine deficiency states have been linked to serious clinical complications in pregnancy for both mother and child, however current assessments of selenium status in the UK pregnant population remains limited. The present study aims to assess selenium and iodine concentrations during pregnancy in a UK based cohort, investigating for the first time potential associations between these two micronutrients. Serum selenium, urinary iodine, serum GPx3, serum SEPP1, serum free triiodothyronine (fT3), serum free thyroxine (fT4), serum TSH and serum thyroglobulin was measured in 70 prospective mothers from the Health & Iodine Status in Babies (HIBA) cohort. Serum samples were collected at three time points spanning gestation (~13-15 weeks, ~24 weeks and ~36 weeks) and quantified using ICP-MS/ELISA methodologies. Longitudinal assessments were performed to monitor how concentrations changed over time. Serum selenium concentration was associated with iodine, relevant biomarkers, dietary intake and birthweight using repeat measure linear regression. Median (interquartile range) serum selenium concentrations across the three time-points of pregnancy were 71.4(16.4), 64.2(12.2) and 57.7(15.3) µg/L, respectively. Adjusted linear regression analysis found significant associations between selenium and GPx3 (p<0.001), SEPP1 (p<0.001) and birthweight (p=0.02, first time point), however no associations between diet and iodine status were observed. This study found that the mothers in this cohort were generally selenium deficient as per recommended guidelines (90-100 µg/L). For the first time within a UK population, selenium concentration was found to be associated with birthweight during early pregnancy with a 10 µg increase in serum selenium concentration leading to a 150 g rise in birthweight. As such, the results of this study could have a major impact on the nutritional guidance recommended to UK mothers, though further research with a larger population is warranted to consolidate findings.