# The Immunological Role of Vitamin D in Primary Immunodeficiencies: A Narrative Review of the Current Literature

## TL;DR

This review explores how vitamin D deficiency affects people with primary immunodeficiencies and highlights its impact on health and treatment outcomes.

## Contribution

The paper provides a narrative review on the role of vitamin D in primary immunodeficiencies and its clinical implications.

## Key findings

- Vitamin D deficiency is linked to more severe clinical conditions in patients with primary immunodeficiencies.
- Calcitriol therapy showed beneficial effects in these patients, emphasizing the need for long-term monitoring.
- Deficiency is associated with complications like osteoporosis, fractures, and hypocalcemia.

## Abstract

Vitamin D is a fat-soluble hormone essential for bone mineralization. In addition to this role, vitamin D is known for its immunomodulatory effects through its binding to intracellular vitamin D receptors (VDRs), which translocate to the nucleus of immune cells, including antigen-presenting cells (APC), B lymphocytes, T lymphocytes and monocytes, thereby modulating the transcription of genes responsible for the immune response. Vitamin D deficiency is associated with an increased risk of developing infections and autoimmune diseases. The purpose of this review is to evaluate vitamin D deficiency in patients with primary immunodeficiency (CVID, XLA, DGS, APECED, SCID, WAS, HIES), to assess its clinical and therapeutic impact. Vitamin D deficiency, often asymptomatic, is associated with more severe clinical conditions in subjects with PID. It can be associated with osteoporosis, fractures, myelofibrosis and endocrine disorders such as hypocalcemia. These patients responded beneficially to calcitriol therapy, underscoring the need for long-term monitoring.