Hashimoto's thyroiditis (HT) is marked by self-tissue destruction as a consequence of an alteration in the adaptive immune response that entails the evasion of immune regulation. Vitamin D carries out an immunomodulatory role that appears to promote immune tolerance. The aim of this study is to elaborate a narrative review of the relationship between vitamin D status and HT and the role of vitamin D supplementation in reducing HT risk by modulating the immune system. There is extensive literature confirming that vitamin D levels are significantly lower in HT patients compared to healthy people. On the other hand, after the supplementation with cholecalciferol in patients with HT and vitamin D deficiency, thyroid autoantibody titers decreased significantly. Further knowledge of the beneficial effects of vitamin D in the prevention and treatment of autoimmune thyroid diseases requires the execution of additional randomized, double-blind, placebo-controlled trials and longer follow-up periods.