Vitamin D in autoimmune diseases

Davide Gatti, Francesca Pistillo, Giulia Bonasera, Giulia Zanetti, Valeria Messina

University of Verona, Rheumatology Unit

DOI 10.30455/2611-2876-2022-3e

That vitamin D cannot be considered as merely a vitamin related to bone metabolism is by now an established fact. Certainly, everyone knows that exposure to sunlight improves our state of well-being. The explanation for this cannot simply be reduced to the production of endorphins by keratinocytes exposed to UV radiation.

There is a great deal of historical evidence for the efficacy of heliotherapy, starting with the Nobel Prize awarded to Niels Ryberg Finsen in 1903 for showing the extraordinary and rapid therapeutic efficacy that exposure to sunlight had on tubercular skin lesions [lupus vulgaris]. Therefore, vitamin D goes far beyond bone metabolism alone, which is also confirmed by the observation that essentially, the vitamin D receptor (VDR) is nearly ubiquitous in our bodies being particularly well represented in extra-skeletal tissues. Furthermore, this receptor has also been found in yeasts and in animals with no skeletal or dental apparatus at all, such as lampreys. Among the extra-skeletal actions of vitamin D, this review will focus on that relating to the modulation of the immune response. 

The VDR is expressed by diverse cells of the immune system (both innate and adaptive). However, many of these cells (especially macrophages and dendritic cells) possess the full enzyme apparatus required to transform vitamin D into its active form, which will then act on the same cell (autocrine activity) or on neighbouring cells (paracrine activity).

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