Vitamin D Receptor Polymorphisms and Immunological Effects of Vitamin D in Hashimoto's Thyroiditis

Vitamin D is involved in numerous processes and is obtained both exogenously and endogenously. Its active form is 1,25-dihydroxycholecalciferol, which exerts its biological effects via the vitamin D receptor (VDR). The main factors influencing VDR density are polymorphisms of the VDR gene, which may affect, e.g., gene mRNA stability and also VDR gene expression. There are four main polymorphic sites within the gene, BsmI, ApaI, FokI and TaqI, and two polymorphisms related to the gene promoter: GATA and Cdx2. One of the functions of vitamin D is to modulate the immune system. It affects T lymphocytes, B lymphocytes and dendritic cells. Currently, vitamin D deficiency is a common global problem that is associated with an increased risk of autoimmune diseases, including Hashimoto's thyroiditis. Numerous studies have demonstrated an association between low vitamin D levels and elevated thyroid-stimulating hormone (TSH) levels, and have also proven the existence of a negative correlation between vitamin D levels andanti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibody titers. Review objectives and a concise summary of the methodology: The review aims to analyze studies examining the relationship between specific VDR polymorphisms, vitamin D levels, and the development of various diseases, with a particular emphasis on Hashimoto's thyroiditis. This review is based on original and review articles written in English published between March 2018-November 2024 searched primarily in the PubMed, and additionally in Google Scholar databases. A narrative review of the literature was conducted.

The presence of specific VDR polymorphisms influences the effectiveness of vitamin D supplementation, but the role of supplementation in the prevention of autoimmune diseases has not been definitively confirmed. To date, studies have primarily involved relatively small groups of patients with significant population heterogeneity, with case-control investigations being the most common. Therefore, further research on larger, more homogeneous groups is recommended to achieve more standardized results. Additionally, the influence of epigenetic factors modulating VDR activity and its interactions with the environmental factors is also important.