Association Between Vitamin D Deficiency and Autoimmune Thyroid Disorder: A Systematic Review

Despite recent evidence that low serum 25-hydroxyvitamin D (25(OH)D) levels and deflects may influence the emergence of autoimmune thyroid disorders (AITD), the relationship between vitamin D deficiency and Graves' disease (GD) and Hashimoto's thyroiditis (HT), which comprise AITD, remains unclear. We retrieved studies that described vitamin D association with HT and GD from PubMed/Medline, Google Scholar, and the Cochrane Library. We included research studies that compared vitamin D levels and deficiency or sufficiency between AITD cases such as HT and GD cases and control subjects. The final assessment comprised 11 studies that recruited 1952 AITD cases (HT and GD) that were published between 2011 and 2021; these were included in the final review. All the included studies were observational, and more precisely, case-control studies that recruited healthy subjects as well as controls. The majority of the studies reviewed indicated that HT and GD patients have a greater prevalence of vitamin D deficiency or low serum 25 (OH)-D levels. Two studies failed to establish an association between vitamin D deficiency and HT and GD disease. In conclusion, vitamin D deficiency or insufficiency can increase the rate of autoimmune diseases such as HT and GD. Randomized controlled trials with a longer follow-up period are needed to confirm the causal relationship between autoimmune thyroid disorder and vitamin D and to provide more reliable insights into the relevance of treatment effects of vitamin D therapy or supplementation.