Association of vitamin D deficiency with COVID-19 infection severity: Systematic review and meta-analysis

Background: We sought to evaluate the association between vitamin D deficiency and the severity of coronavirus disease 2019 (COVID-19) infection. Methods: Multiple databases from 1 January 2019 to 3 December 2020 were searched for observational studies evaluating the association between vitamin D deficiency and severity of COVID-19 infection. Independent reviewers selected studies and extracted data for the review. The main outcomes of interest were mortality, hospital admission, length of hospital stay and intensive care unit admission. Results: Seventeen observational studies with 2756 patients were included in the analyses. Vitamin D deficiency was associated with significantly higher mortality (odds ratio [OR]: 2.47, 95% confidence interval [CI]: 1.50–4.05; 12 studies; hazard ratio [HR]: 4.11, 95% CI: 2.40–7.04; 3 studies), higher rates of hospital admissions (OR: 2.18, 95% CI: 1.48–3.21; 3 studies) and longer hospital stays (0.52 days; 95% CI: 0.25–0.80; 2 studies) as compared to nonvitamin D deficient status. Subgroup analyses based on different cut-offs for defining vitamin D deficiency, study geographic locations and latitude also showed similar trends. Conclusions: Vitamin D deficiency is associated with greater severity of COVID-19 infection. Further studies are warranted to determine if vitamin D supplementation can decrease the severity of COVID-19.