Randomized controlled trial of the effect of selenium supplementation on thyroid function in the elderly in the United Kingdom.
BACKGROUND
Thyroid function depends on the essential trace mineral selenium, which is at the active center of the iodothyronine deiodinase enzymes that catalyze the conversion of the prohormone thyroxine (T(4)) to the active form of thyroid hormone, triiodothyronine (T(3)).


OBJECTIVE
Because selenium intake in the United Kingdom has fallen during the past 25 y, we wanted to determine whether current selenium status might be limiting conversion of T(4) to T(3) in the elderly, in whom marginal hypothyroidism is relatively common.


METHODS
We investigated the effect of selenium supplementation in a double-blind, placebo-controlled trial in 501 elderly UK volunteers. Similar numbers of men and women from each of 3 age groups, 60-64 y, 65-69 y, and 70-74 y, were randomly allocated to receive 100, 200, or 300 microg Se/d as high-selenium yeast or placebo yeast for 6 mo. As part of the study, plasma selenium, thyroid-stimulating hormone, and total and free T(3) and T(4) were measured. Data from 368 euthyroid volunteers who provided blood samples at baseline and 6 mo were analyzed.


RESULTS
Although selenium status at baseline correlated weakly with free T(4) (r = -0.19, P < 0.001) and with the ratio of free T(3) to free T(4) (r = 0.12, P = 0.02), we found no evidence of any effect of selenium supplementation on thyroid function, despite significant increases in plasma selenium. However, baseline plasma selenium in our study (x: 91 microg/L) was somewhat higher than in previous supplementation studies in which apparently beneficial effects were seen.


CONCLUSIONS
We found no indication for increasing selenium intake to benefit T(4) to T(3) conversion in the elderly UK population.
Rayman
Margaret P
MP
Nutritional Sciences Division, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom. m.rayman@surrey.ac.uk
Thompson
Alexander J
AJ
Bekaert
Bram
B
Catterick
Janet
J
Galassini
Rachel
R
Hall
Emma
E
Warren-Perry
Margaret
M
Beckett
Geoffrey J
GJ
D000368:Aged; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000188:drug therapy / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D012643:Selenium / Q000097:blood; D018036:Selenium Compounds / Q000008:administration & dosage*; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D006113:United Kingdom / Q000453:epidemiology
D018036:Selenium Compounds; D014284:Triiodothyronine; D013972:Thyrotropin; D012643:Selenium; D013974:Thyroxine