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

CONTEXT: Autoimmune thyroid disorders have been linked to vitamin D deficiency, but an effect of vitamin D supplementation is not established. OBJECTIVE: Our objective was to test whether vitamin D compared with placebo could reduce thyroid autoantibodies. DESIGN: Predefined additional analyses from a randomized, double-blind, placebo-controlled trial. SETTING: The study was conducted in different community centers in Oslo, Norway. PARTICIPANTS: 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. INTERVENTION: Daily supplementation with 25 µg (1000 IU) vitamin D(3), 10 µg (400 IU) vitamin D(3), or placebo for 16 weeks. OUTCOME MEASURE: 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). RESULTS: 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)D(3) increased from 26 to 49 nmol/L in the combined supplementation group, but there was no change in the placebo group. CONCLUSION: Vitamin D(3) 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.