Vitamin D: immune function, inflammation, infections and auto-immunity

ABSTRACTABSTRACTVitamin D plays an active role beyond mineral metabolism and skeletal health, including regulation of the immune system. Vitamin D deficiency is widely prevalent, and observational studies link low vitamin D status to a risk of infections and auto-immune disorders. Reports indicate an inverse relationship between vitamin D status and such conditions. This review details vitamin D signalling interactions with the immune system and provides experimental and clinical evidence evaluating vitamin D status, vitamin D supplementation and host susceptibility to infections, inflammation and auto-immunity. The published literature including related reviews, systematic reviews, meta-analyses, randomised controlled trials (RCTs), observational studies and basic science reports have been synthesised. Meta-analyses of observational studies have demonstrated a link between low vitamin D status and risk of acute respiratory infections, COVID-19 disorders, multiple sclerosis, type 1 diabetes (T1DM), inflammatory bowel disease (IBD), systemic lupus erythematosus and other auto-immune disorders. Observational studies suggest that vitamin D supplementation may protect against several infectious and auto-immune conditions. Meta-analyses of RCTs had mixed results, demonstrating a small protective role for vitamin D supplementation against acute respiratory infections, especially in those with vitamin D deficiency and children, and providing modest benefits for the management of T1DM and IBD. Vitamin D status is inversely associated with the incidence of several infectious and auto-immune conditions. Supplementation is recommended for those with vitamin D deficiency or at high risk of deficiency, and it might provide additional benefit in acute respiratory infections and certain auto-immune conditions.KEYWORDS: COVID-1925-hydroxyvitamin Dvitamin D receptorCYP27B1metabolismricketsrespiratory Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by the no funding.Notes on contributorsCasey R. JohnsonCasey Johnson is a paediatric gastroenterology fellow at Boston Children's Hospital and former paediatric resident at Mayo Clinic.Tom D. ThacherTom Thacher is the Parker D. and Isabella G. Sanders Professor of Family Medicine at Mayo Clinic. His international research has focused on nutritional rickets and vitamin D.