Effect of Vitamin D on Thyroid Autoimmunity: A Randomized, Double-Blind, Controlled Trial Among Ethnic Minorities

Autoimmune thyroid disorders have been linked to vitamin D deficiency, but an effect of vitamin D supplementation is not established.

Our objective was to test whether vitamin D compared with placebo could reduce thyroid autoantibodies.

Predefined additional analyses from a randomized, double-blind, placebo-controlled trial.

The study was conducted in different community centers in Oslo, Norway.

A total of 251 presumed healthy men and women, aged 18 to 50 years, with backgrounds from South Asia, the Middle East, and Africa were included.

Daily supplementation with 25 µg (1000 IU) vitamin D₃, 10 µg (400 IU) vitamin D₃, or placebo for 16 weeks.

Difference in preintervention and postintervention antithyroid peroxidase antibody (TPOAb) levels. Additional outcomes were differences in thyroid-stimulating hormone (TSH) and free fraction of thyroxine (fT4).

There were no differences in change after 16 weeks on TPOAb (27 kU/L; 95% CI, -17 to 72; P = 0.23), TSH (-0.10 mU/L; 95% CI, -0.54 to 0.34; P = 0.65), or fT4 (0.09 pmol/L; 95% CI, -0.37 to 0.55; P = 0.70) between those receiving vitamin D supplementation or placebo. Mean serum 25(OH)D₃ increased from 26 to 49 nmol/L in the combined supplementation group, but there was no change in the placebo group.

Vitamin D₃ supplementation, 25 µg or 10 µg, for 16 weeks compared with placebo did not affect TPOAb level in this randomized, double-blind study among participants with backgrounds from South Asia, the Middle East, and Africa who had low vitamin D levels at baseline.