The Impact of Vitamin D on Immune Function and Its Role in Hashimoto's Thyroiditis: A Narrative Review

Vitamin D, an essential nutrient, plays a crucial role in numerous biological functions, acting as a hormone and being important for the proper functioning of the immune system. This review illustrates the interactions between adequate vitamin D levels and an appropriate immune response, highlighting the implications for Hashimoto's thyroiditis (HT), a chronic inflammation of the thyroid characterized by the production of autoantibodies. A comprehensive review of the existing literature shows that vitamin D inhibits the secretion of pro-inflammatory cytokines, leading to an improvement in the clinical picture in HT by switching from a pro-inflammatory to immune balance. Vitamin D supplementation has been shown to reduce elevated serum levels of thyroid peroxidase antibodies, a key marker of HT. Although the results are conflicting, the evidence suggests that an adequate vitamin D intake supports the immune function and counteracts autoimmune conditions such as HT by improving their symptoms. There is evidence of vitamin D's key role in supporting the immune system function and managing autoimmunity, such as in HT. An adequate vitamin D intake is crucial for improving the clinical picture and the symptoms of HT.