# The Role of Vitamin D in Autoimmune Diseases

## TL;DR

This review explores how vitamin D influences immune responses and its potential role in managing autoimmune diseases like multiple sclerosis and rheumatoid arthritis.

## Contribution

The paper provides a comprehensive overview of vitamin D's molecular mechanisms in immune regulation and its implications for autoimmune diseases.

## Key findings

- Vitamin D deficiency is linked to the pathogenesis of autoimmune diseases such as multiple sclerosis and type 1 diabetes.
- Vitamin D promotes tolerogenic immune responses and suppresses inflammation through its receptor interaction.
- Supplementation may help reduce disease activity in immune-mediated disorders.

## Abstract

Vitamin D is a steroid hormone whose relevant immunomodulatory role has been widely described. Therefore, its contribution to the pathogenesis of immune-mediated diseases is an important and ongoing matter of research. Specifically, the active form of vitamin D, i.e., 1,25-dihydroxyvitamin D, through the interaction with its receptor, exerts different activities on the innate and adaptive immune system, among which are suppression of inflammation and promotion of tolerogenic responses. Indeed, vitamin D insufficiency/deficiency has been related to the pathogenesis and/or disease activity of several autoimmune diseases, including, amongst others, multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and type 1 diabetes mellitus. Based on these premises, in this review, we will describe the main molecular mechanisms modulated by vitamin D in the regulation of immune responses, including the induction of immune tolerance. Moreover, we will focus on the current knowledge regarding the contribution of vitamin D depletion to the aforementioned autoimmune diseases, seeking to provide evidence as to why its supplementation in the context of these immune-mediated disorders may potentially ameliorate disease activity and its related clinical manifestations.