Randomized controlled trial of the effect of selenium supplementation on thyroid function in the elderly in the United Kingdom.
Level 2 - randomized trial
Individual randomized double-blind placebo-controlled trial
PubMed 18258627 · doi:10.1093/ajcn/87.2.370
What was done
A double-blind, placebo-controlled trial randomized 501 elderly UK volunteers aged 60-74 years (stratified by sex across age bands 60-64, 65-69, and 70-74 y) to receive placebo yeast or high-selenium yeast at doses of 100, 200, or 300 mcg Se/day for 6 months. Researchers measured plasma selenium, thyroid-stimulating hormone (TSH), and total and free T3 and T4 at baseline and 6 months. Data were analyzed from 368 euthyroid volunteers who completed blood sampling at both timepoints.
What was found
Baseline plasma selenium averaged 91 mcg/L and correlated weakly with free T4 (r = -0.19, P < 0.001) and the free T3 to free T4 ratio (r = 0.12, P = 0.02). Selenium supplementation significantly increased plasma selenium, but showed no evidence of any effect on thyroid function parameters or T4-to-T3 conversion. Absolute numerical values and effect sizes for post-supplementation thyroid measures were not reported in the abstract.
Why it matters
Despite reported historical declines in selenium intake in the UK, these findings indicate that routine selenium supplementation does not improve thyroid hormone status in older euthyroid adults who already possess baseline plasma selenium levels near 91 mcg/L.
Limits
Only 368 of the 501 randomized participants were included in the final analysis due to missing paired samples or non-euthyroid status. The abstract omits exact numerical values, standard deviations, and confidence intervals for post-treatment thyroid hormone concentrations. The results cannot be generalized to severely selenium-deficient populations or patients with established hypothyroidism.
Cited by
- supports Selenium is vital for the enzymatic conversion of thyroid hormone T4 to T3.