Therapeutic and prognostic role of vitamin D for COVID-19 infection: A systematic review and meta-analysis of 43 observational studies

Vitamin D modulates the systemic inflammatory response through interaction with immune system. As such, it has a possible protective role against the risk of respiratory tract infections and other diseases. It may be useful in particular, during COVID-19 pandemic. PubMed, the Cochrane Library, and EMBASE were searched from inception until January 31, 2021, for observational or clinical studies reporting the prognosis (and therapeutic effect) of COVID-19 infection in patients with deficient vitamin D levels. The infection rate, severity, and death from COVID-19 infection were pooled to provide an odds ratio with a 95 % confidence interval (OR 95 % CI). An OR 1 was associated with the worst outcome in deficient compared with nondeficient patients. We assessed the association between vitamin D and risk, severity, and mortality for COVID-19 infection, through a review of 43 observational studies. Among subjects with deficient vitamin D values, risk of COVID-19 infection was higher compared to those with replete values (OR = 1.26; 95 % CI, 1.19-1.34; P < .01). Vitamin D deficiency was also associated with worse severity and higher mortality than in nondeficient patients (OR = 2.6; 95 % CI, 1.84-3.67; P < .01 and OR = 1.22; 95 % CI, 1.04-1.43; P < .01, respectively). Reduced vitamin D values resulted in a higher infection risk, mortality and severity COVID-19 infection. Supplementation may be considered as preventive and therapeutic measure.