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Effect of Selenium Supplementation on Thyroid Function in UK Pregnant Women: a Randomised, Controlled Pilot Trial

Selenium (Se) is an essential trace mineral which is important for human health including immune and thyroid functions. The thyroid has the highest Se concentration of all tissues and maternal thyroid function directly influences fetal development. This study explores the effect of Se supplementation on thyroid function in UK pregnant women. At 12wks’ gestation, 230 pregnant women were randomized to 60mg/day Se (high-Se yeast) or a yeast placebo in the SPRINT trial (Se in Pregnancy Intervention), and remained on treatment until the end of pregnancy. Whole-blood Se was determined at 12 and 35wks by ICP-MS. Plasma selenoprotein P (SEPP1), an indicator of Se status, was measured at 35wks by ELISA. Thyroid-stimulating hormone (TSH), free thyroxine (FT4) and antithyroid peroxidise antibodies (TPOAb) were measured at 12, 20 and 35wks by immunoassay. Whole-blood Se concentration did not differ between Se and placebo groups at baseline. At 35 wks, both whole-blood Se and plasma SEPP1 concentrations were significantly higher in the Se group than in the placebo group (both, P<0.000). Plasma SEPP1concentration at 35wks was positively correlated with whole-blood Se (Spearman’s r = 0.776, P = 0.000) in the whole population reflecting the fact that even in many of the women allocated to Se treatment, SEPP1did not reach a plateau (see Fig. 1). Hence the combination of Se dose and treatment time did not achieve nutritional Se sufficiency, as measured by plasma SEPP1.