Submitted to: Journal of Trace Elements in Medicine and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2007
Publication Date: 1/15/2008
Citation: Hawkes, W.C., Keim, N.L., Richter, D., Gustafson, M.B., Gale, B., Mackey, B.E., Bonnel, E. 2008. Response of selenium status indicators to supplementation of healthy north american men with high-selenium yeast. Journal of Trace Elements in Medicine and Biology. Vol.122:107-121, 2008.
Interpretive Summary: The upper tolerable intake limit for selenium was set at 400 micrograms per day by the National Academy of Sciences in 2000. Our previous study of 5 men confined in our research unit and eating high-selenium foods suggested that intakes of only 300 micrograms per day might have adverse effects on energy metabolism and weight control. In clinical trials, selenium intakes of 300-400 micrograms per day have been found to protect against prostate cancer and it is important to clarify whether these intakes are safe for healthy people. Selenium intakes high enough to protect against cancer are only achieved in the United States by taking nutritional supplements, typically in the form of high-selenium yeast tablets. We tested the health effects of taking 300 micrograms of selenium in high-selenium yeast tablets for one year in 42 healthy, free-living men who were already getting an average of 135 micrograms per day from the usual diets. We found that a combined selenium intake of 435 micrograms per day had no detectable effect on energy metabolism, thyroid hormones or body weight. Our research shows that the upper tolerable intake limit includes an adequate safety factor for healthy men. This information will be useful in the next review of the dietary reference intervals by the National Academy of Sciences. Our results are useful for consumers, who can be assured that taking selenium supplements as prescribed is completely safe. Our demonstration of the safety of high-selenium yeast supplements will help remove barriers to testing selenium against cancer.
Technical Abstract: In a prior study, we observed decreased serum 3,3’,5-triiodothyronine (t3), increased serum thyrotropin and increased body weight in 5 men fed 297 'g/d of selenium (Se) in foods naturally high in Se while confined in a metabolic research unit. In an attempt to replicate and confirm those observations, we conducted a randomized study of high-Se yeast supplements (300'g/d) or placebo yeast administered to 42 healthy free-living men for 48 weeks. Serum T4, T3 and thyrotropin did not change in supplemented or control subjects. Body weight increased during the 48-week treatment period by 1.5 kg in both groups and remained at that level for the 48-week follow-up period. Body fat increased by 1.2 kg in both groups. Energy intake was not different between the groups and remained unchanged during the treatment period. Dietary intake of Se, macronutrients and micronutrients was not different between groups and remained unchanged during treatment. These results suggest that our previous observations were confounded by a dietary component other than Se or of the particular diet composition used. Because of the high dose and long administration period, this study provides strong evidence that Se supplements do not affect thyroid hormone metabolism, body composition, or weight gain.