Does selenium supplementation affect thyroid function? Results from a randomized, controlled, double-blinded trial in a Danish population.
OBJECTIVE
Selenium is present in the active site of proteins important for thyroid hormone synthesis and metabolism. The objective of this study is to investigate the effect of selenium supplementation in different doses on thyroid function, under conditions of suboptimal dietary selenium intake.


METHODS
The Danish PREvention of Cancer by Intervention with SElenium pilot study (DK-PRECISE) is a randomized, double-blinded, placebo-controlled trial. A total of 491 males and females aged 60-74 years were randomized to 100 μg (n=124), 200 μg (n=122), or 300 μg (n=119) selenium-enriched yeast or matching yeast-based placebo tablets (n=126). A total of 361 participants, equally distributed across treatment groups, completed the 5-year intervention period.


METHODS
Plasma samples were analyzed for selenium and serum samples for TSH, free triiodothyronine (FT3), and free thyroxine (FT4) at baseline, and after 6 months, and 5 years of supplementation.


RESULTS
Plasma selenium concentrations increased significantly and dose-dependently in treatment groups receiving selenium (P<0.001). Serum TSH and FT4 concentrations decreased significantly and dose-dependently by 0.066 mIU/l (P=0.010) and 0.11 pmol/l (P=0.015), respectively, per 100 μg/day increase, with insignificant differences between 6 months and 5 years. No significant effects were found for FT3 and FT3:FT4 ratio.


CONCLUSIONS
In euthyroid subjects, selenium supplementation minutely and dose-dependently affects thyroid function, when compared with placebo, by decreasing serum TSH and FT4 concentrations. Based on these findings, selenium supplementation is not warranted under conditions of marginal selenium deficiency. However, a role for selenium supplementation in the treatment of autoimmune thyroid diseases is still unresolved.
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark kristian.winther@rsyd.dk.
Kristian Hillert
KH
Winther
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Steen Joop
SJ
Bonnema
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Frederik
F
Cold
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Birgit
B
Debrabant
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Mads
M
Nybo
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Søren
S
Cold
Department of Endocrinology and MetabolismOdense University Hospital, Kloevervaenget 10, 6. Sal, DK-5000 Odense C, DenmarkDepartment of OncologyOdense University Hospital, Odense, DenmarkDepartment of EpidemiologyBiostatistics and Biodemography, University of Southern Denmark, Odense, DenmarkDepartment of Clinical Biochemistry and PharmacologyOdense University Hospital, Odense, Denmark.
Laszlo
L
Hegedüs
D000368:Aged; D003718:Denmark; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012643:Selenium / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood / Q000187:drug effects*; D013974:Thyroxine / Q000097:blood / Q000187:drug effects*; D013997:Time Factors; D014131:Trace Elements / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D014284:Triiodothyronine / Q000097:blood / Q000187:drug effects*; D015002:Yeast, Dried / Q000008:administration & dosage
D014131:Trace Elements; D014284:Triiodothyronine; D013972:Thyrotropin; D012643:Selenium; D013974:Thyroxine