title: Effects of selenomethionine supplementation on selenium status and thyroid hormone concentrations in healthy adults.
abstract: BACKGROUND
  Selenium, a potential cancer prevention agent currently being tested against prostate cancer in the Selenium and Vitamin E Cancer Prevention Trial (SELECT), plays an integral role in thyroid metabolism. The effects of long-term selenium supplementation on thyroid hormone concentrations are unknown.
  
  
  OBJECTIVE
  The objective was to investigate the effects of long-term selenium supplementation on thyroid hormone concentrations.
  
  
  METHODS
  Twenty-eight healthy adults took 200 microg selenomethionine/d for 28 mo. The thyroid hormones triiodothyronine (T3), thyroxine (T4), and thyrotropin (TSH) were measured in plasma for 4 mo before supplementation and quarterly during supplementation. The assay methods were changed midstudy; the results of the 2 methods were not comparable. Therefore, one analysis was conducted based on the results of the first method, and a second analysis was based on all of the data, adjusted for the change. Serial data collection permitted a test for trends rather than simply a difference between initial and final values.
  
  
  RESULTS
  By 9 mo, mean (+/-SEM) plasma selenium concentrations had increased from 1.78 +/- 0.07 micromol/L at baseline to 2.85 +/- 0.11 micromol/L for men and from 1.64 +/- 0.04 to 3.32 +/- 0.1.2 micromol/L for women. T3 concentrations in men increased 5% per year (P = 0.01). T4 and TSH concentrations were unchanged.
  
  
  CONCLUSIONS
  Selenium supplementation produced no clinically significant changes in thyroid hormone concentrations. A small but statistically significant increase in T3 concentrations was noted in men, with no corresponding decreases in TSH. A subset of SELECT subjects might be monitored periodically for changes during long-term selenium supplementation.
authors.affiliation: Grand Forks Human Nutrition Research Center, US Department of Agriculture, Agricultural Research Service, Grand Forks, ND 55202, USA. gerald.combs@ars.usda.gov
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Combs
authors.forename: Douglas N
authors.initials: DN
authors.lastname: Midthune
authors.forename: Kristine Y
authors.initials: KY
authors.lastname: Patterson
authors.forename: Wesley K
authors.initials: WK
authors.lastname: Canfield
authors.forename: A David
authors.initials: AD
authors.lastname: Hill
authors.forename: Orville A
authors.initials: OA
authors.lastname: Levander
authors.forename: Philip R
authors.initials: PR
authors.lastname: Taylor
authors.forename: James E
authors.initials: JE
authors.lastname: Moler
authors.forename: Blossom H
authors.initials: BH
authors.lastname: Patterson
mesh_terms: D000328:Adult; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012643:Selenium / Q000097:blood*; D012645:Selenomethionine / Q000008:administration & dosage / Q000494:pharmacology*; D012737:Sex Factors; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014131:Trace Elements / Q000008:administration & dosage / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014131:Trace Elements; D014284:Triiodothyronine; D013972:Thyrotropin; D012645:Selenomethionine; D012643:Selenium; D013974:Thyroxine