Effects of vitamin D on thyroid autoimmunity markers in Hashimoto's thyroiditis: systematic review and meta-analysis

To perform a meta-analysis of randomized controlled trials to evaluate the efficacy of vitamin D supplementation on thyroid autoimmunity markers in Hashimoto's thyroiditis (HT).

This meta-analysis included randomized controlled clinical trials identified by a systematic search of electronic databases (PubMed®, MEDLINE®, EMBASE, The Cochrane Library, China National Knowledge Infrastructure) from inception to August 2020. All studies included patients with HT that received vitamin D supplementation irrespective of the doses administered or the duration of treatment. The primary and secondary outcome measures were thyroid peroxidase antibody (TPOAb) and/or thyroglobulin antibody (TGAb) titres.

Eight studies (n = 652) were included. There was significant heterogeneity between the studies. Using a random-effect model, vitamin D supplementation reduced TPOAb titre (standardized mean difference [SMD]: -1.11; 95% confidence interval [CI]: 1-1.92, -0.29) and TGAb titre (SMD: -1.12; 95% CI: -1.96, -0.28). A subgroup analysis demonstrated that vitamin D supplementation for >3 months resulted in a decrease in TPOAb titre (SMD: -1.66, 95% CI: -2.91, -0.41) but treatment ≤3 months was ineffective. Treatment with vitamin D₃ decreased TPOAb titre (SMD: -1.48; 95% CI: -2.53, -0.42) whereas vitamin D did not.

These data suggest that vitamin D reduces autoantibody titre in patients with HT.