Effects of selenomethionine supplementation on selenium status and thyroid hormone concentrations in healthy adults.
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.
Combs
Gerald F
GF
Grand Forks Human Nutrition Research Center, US Department of Agriculture, Agricultural Research Service, Grand Forks, ND 55202, USA. gerald.combs@ars.usda.gov
Midthune
Douglas N
DN
Patterson
Kristine Y
KY
Canfield
Wesley K
WK
Hill
A David
AD
Levander
Orville A
OA
Taylor
Philip R
PR
Moler
James E
JE
Patterson
Blossom H
BH
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*
D014131:Trace Elements; D014284:Triiodothyronine; D013972:Thyrotropin; D012645:Selenomethionine; D012643:Selenium; D013974:Thyroxine