A review of the critical role of vitamin D in the functioning of the immune system and the clinical implications of vitamin D deficiency

Abstract

This review looks at the critical role of vitamin D in improving barrier function, production of antimicrobial peptides including cathelicidin and some defensins, and immune modulation. The function of vitamin D in the innate immune system and in the epithelial cells of the oral cavity, lung, gastrointestinal system, genito‐urinary system, skin and surface of the eye is discussed. Clinical conditions are reviewed where vitamin D may play a role in the prevention of infections or where it may be used as primary or adjuvant treatment for viral, bacterial and fungal infections. Several conditions such as tuberculosis, psoriasis, eczema, Crohn's disease, chest infections, wound infections, influenza, urinary tract infections, eye infections and wound healing may benefit from adequate circulating 25(OH)D as substrate. Clinical diseases are presented in which optimization of 25(OH)D levels may benefit or cause harm according to present day knowledge. The safety of using larger doses of vitamin D in various clinical settings is discussed.

Deficiency in 25-Hydroxyvitamin D and 30-Day Mortality in Patients With Severe Sepsis and Septic Shock

“…18,19 The mechanism through which vitamin D deficiency is associated with increased mortality in patients with sepsis may be related to its immunological effects. Studies 22,23 suggest that vitamin D can regulate adaptive and innate immune responses. Receptors for vitamin D are nuclear receptors that are expressed on many immune cells, including activated B and T cells, macrophages, and other antigen-presenting cells.…”

Nutritional Aspects of Gastrointestinal Wound Healing

“…These proteins preserve the integrity of the barriers in the gastrointestinal tract, control the communal bacteria that usually reside in the gastrointestinal tract, and help to resist invasion by other pathogens. 19 The physiologically active hormone also upregulates occludin, connexin 43, and E-cadherin activity, which is required for tight junctions, gap junctions, and adherens junctions in the intestinal mucosa, respectively. 19 Vitamin D may also play a role in reducing fibrosis in Crohn's disease, as an analog reduces profibrotic responses in colonic myofibroblasts.…”

Innate Immune Responses in the Geriatric Population

“…It promotes innate immune responses to TLR activation by Mycobacterium tuberculosis. 1,25(OH)2vit D increases cathelicidin, a antimicrobial peptide after activation of TLR1/2 but inhibits the maturation of monocytederived dendritic cells (Bikle, 2009;Hewison, 2010;Schwalfenberg, 2011). By increasing cathelicidin, vitamin D supplementation improves the outcome of many diseases: it reduced dental caries and Helicobacter pylori infections.…”

“…By increasing cathelicidin, vitamin D supplementation improves the outcome of many diseases: it reduced dental caries and Helicobacter pylori infections. Vitamin D insufficiency is associated with Crohn's disease, pour outcome in severe pneumonia and urinary tract infections (Schwalfenberg, 2011). Vitamin D improves physical barrier by stimulating gap junctions genes, adherent genes and tight junction genes (Schwalfenberg, 2011).…”