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United States Department of Agriculture

Agricultural Research Service

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

Authors
item Combs, Gerald
item Midthune, Douglas - NATL CANCER INSTITUTE
item Patterson, Kristine
item Canfield, Wesley
item Hill, Arland
item Levander, Orville
item Taylor, Philip - NATL CANCER INSTITUTE
item Moler, James - INFORMATION MGMT SVS
item Patterson, Blossom - NATL CANCER INSTITUTE

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2009
Publication Date: June 1, 2009
Repository URL: http://handle.nal.usda.gov/10113/31819
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.

Last Modified: 10/25/2014