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Title: Effects of Selenomethionine Supplementation on Selenium Status and Thyroid Hormone Concentrations in Healthy Adults

Author
item Combs, Gerald
item MIDTHUNE, DOUGLAS
item Patterson, Kristine
item Canfield, Wesley
item Hill, Arland
item Levander, Orville
item TAYLOR, PHILIP
item MOLER, JAMES
item PATTERSON, BLOSSOM

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2009
Publication Date: 6/1/2009
Citation: Combs, G.F., Midthune, D.N., Patterson, K.K., Canfield, W.K., Hill, A.D., Levander, O.A., Taylor, P.R., Moler, J.E., Patterson, B.H. 2009. Effects of Selenomethionine Supplementation on Selenium Status and Thyroid Hormone Concentrations in Healthy Adults. American Journal of Clinical Nutrition. 89(6):1808-1814.

Interpretive Summary: This paper reports the results of an intervention study in which 28 healthy adults were given a daily supplement of selenium (200 mcg/d) for two years over which time the effects on thyroid status were measured. This was a follow-up to a previous, but small study that reported selenium supplementation to increase circulating levels of thyroid hormone, also called T3. We found selenium supplementation to increase plasma selenium by nearly 60% within 12 months, but not to affect serum levels of T3 or its precursor T4. We did, however, note a suggestion of a long-term drop in serum levels of thyroid-stimulating hormone (TSH). We conclude that selenium supplementation does not significantly affect thyroid hormone status in healthy Americans.

Technical Abstract: Background: Selenium (Se) is a component of the iodothyronine 5'-deiodinases that convert tetraiodothyronine (T4) to thyroid hormone (T3). One study has suggested that six Se-adequate American males responded to short-term (120 d) Se-supplementation with decreased serum T3 followed by increased thyroid-stimulating hormone (TSH) and 0.8 kg increased body weight. Follow-up on that report is highly relevant to the some ~ 17,000 men currently taking Se (200 mcg/d) in SELECT, a clinical trial designed to test the hypothesis that long-term supplementation with Se may reduce the incidence of prostate cancer. Objective: The objective of this study was to determine the effects of both short- and long-term supplemental on thyroid hormone status of healthy men and women within a study designed to characterize the effects of Se-supplementation on their Se metabolism. Methods: Healthy adults, 13 males and 15 females, were given a daily oral supplement of L-selenomethionine providing 200 mcg Se for 28 mos. Thyroid hormones (T4, T3, TSH) were measured in plasma twice prior to supplementation and then quarterly while supplemented. Results: Subjects’ plasma Se increased from 148+/-50 ng/ml to 233+/-23 ng/ml within 12 mos. No significant changes were detected between baselin and month 28 for either serum T3 (baseline 108.1+/-20.9 ng/dl) or T4 (6.8+/-1.4 mcg/dl) levels. However, TSH levels rose, then began declining after 9-12 months. The baseline level of 1.9±9 mIU/ml ultimately decreased by 0.3 mIU/ml, (p=.05). These changes were independent of seasonal effects. Conclusion: Selenium supplementation does not significantly affect thyroid hormone status in healthy Americans, but there is a suggestion that long-term supplementation may affect TSH levels.