Randomized controlled trial of the effect of selenium supplementation on thyroid function in the elderly in the United Kingdom.

BACKGROUND: Thyroid function depends on the essential trace mineral selenium, which is at the active center of the iodothyronine deiodinase enzymes that catalyze the conversion of the prohormone thyroxine (T(4)) to the active form of thyroid hormone, triiodothyronine (T(3)). OBJECTIVE: Because selenium intake in the United Kingdom has fallen during the past 25 y, we wanted to determine whether current selenium status might be limiting conversion of T(4) to T(3) in the elderly, in whom marginal hypothyroidism is relatively common. DESIGN: We investigated the effect of selenium supplementation in a double-blind, placebo-controlled trial in 501 elderly UK volunteers. Similar numbers of men and women from each of 3 age groups, 60-64 y, 65-69 y, and 70-74 y, were randomly allocated to receive 100, 200, or 300 microg Se/d as high-selenium yeast or placebo yeast for 6 mo. As part of the study, plasma selenium, thyroid-stimulating hormone, and total and free T(3) and T(4) were measured. Data from 368 euthyroid volunteers who provided blood samples at baseline and 6 mo were analyzed. RESULTS: Although selenium status at baseline correlated weakly with free T(4) (r = -0.19, P < 0.001) and with the ratio of free T(3) to free T(4) (r = 0.12, P = 0.02), we found no evidence of any effect of selenium supplementation on thyroid function, despite significant increases in plasma selenium. However, baseline plasma selenium in our study (x: 91 microg/L) was somewhat higher than in previous supplementation studies in which apparently beneficial effects were seen. CONCLUSION: We found no indication for increasing selenium intake to benefit T(4) to T(3) conversion in the elderly UK population.

Impact of selenium on mood and quality of life: a randomized, controlled trial.

BACKGROUND: Selenium is known to be important to the brain. Three small, published studies have suggested an effect of selenium supplementation or deprivation on mood in healthy volunteers. We investigated these findings on a much larger scale. METHODS: In this double-blind, placebo-controlled intervention, 501 UK participants aged 60-74 were randomly allocated to receive 100, 200 or 300 microg selenium/d as high-selenium yeast or placebo yeast. Mood (Profile of Moods States - Bipolar Form [POMS-BI] questionnaire), "quality of life" (Short Form 36 [SF-36] questionnaire) and plasma selenium were measured at baseline and six months. RESULTS: Supplementation significantly increased plasma selenium above baseline values: from an overall mean (SD) of 90(19) ng/g to 91(26), 144(27), 191(41) and 227(53) ng/g in the placebo, 100, 200, 300 microg selenium groups respectively (p < .001). Four hundred forty-eight participants completed the POMS-BI questionnaires at both time points, with no significant differences in total mood or mood-subscale scores seen between doses. After six months of supplementation, mean (SD) total mood scores for the four doses were 163(36), 161(37), 162(33), 162(34), F(3,443) = .25, p = .86. Quality of life was similarly unaffected. CONCLUSIONS: There was no evidence that selenium supplementation benefited mood or quality of life in these elderly volunteers. Though this is at odds with some previous results, our robust study design, much larger sample size and longer supplementation period, together with the evidence that the brain is a privileged site for selenium retention, suggest that this is a reliable finding.