A systematic review and meta-analysis of effect of vitamin D levels on the incidence of COVID-19

Background: Coronavirus disease 2019 (COVID-19) is a disease primarily affecting the respiratory tract, however due to the nature of the pathogenesis it is able to affect the whole body. So far, no causative treatment has been found and the main strategy when dealing with COVID-19 relies on widespread vaccination programs and symptomatic treatment. Vitamin D due to its ability to modulate the immu-nological system has been proposed as a factor playing role in the organism response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Therefore, we decided to perform this me-ta-analysis which aimed to establish a connection between vitamin D status and COVID-19 infection. Methods: Study was designed as a systematic review and meta-analysis. PubMed, EMBASE, Web of Science, Cochrane Collaboration Databases and Scopus electronic databases were searched for relevant studies from database inception to May 10 ^th, 2021. Mean differences (MDs) with their 95% confidence intervals (CI) were calculated. Results: Thirteen studies providing data for 14,485 participants met the inclusion criteria. Mean vitamin D levels in SARS-CoV-2 negative patients was 17.7 ± 6.9 ng/mL compared to SARS-CoV-2 positive patients 14.1 ± 8.2 ng/mL (MD = 3.93; 95% CI 2.84–5.02; I ² = 99%; p < 0.001). Conclusions: Low serum vitamin D levels are statistically significantly associated with the risk of COVID-19 infection. Supplementation of vitamin D especially in the deficiency risk groups is indicated.