Prognostic and therapeutic role of vitamin D in COVID-19: systematic review and meta-analysis

Abstract

Purpose

Vitamin D deficiency/insufficiency may increase the susceptibility to COVID-19. We aimed to determine the association between vitamin D deficiency/insufficiency and susceptibility to COVID-19, its severity, mortality and role of vitamin D in its treatment.

Methods

We searched CINHAL, Cochrane library, EMBASE, PubMED, Scopus, and Web of Science up to 30.05.2021 for observational studies on association between vitamin D deficiency/insufficiency and susceptibility to COVID-19, severe disease and death among adults, and, randomized controlled trials (RCTs) comparing vitamin D treatment against standard care or placebo, in improving severity or mortality among adults with COVID-19. Risk of bias was assessed using Newcastle-Ottawa scale for observational studies and AUB-KQ1 Cochrane tool for RCTs. Study-level data were analyzed using RevMan 5.3 and R (v4∙1∙0). Heterogeneity was determined by I  ² and sources were explored through pre-specified sensitivity analyses, subgroup analyses and meta-regressions.

Results

Of 1877 search results, 76 studies satisfying eligibility criteria were included. Seventy-two observational studies were included in the meta-analysis (n=1976099). Vitamin D deficiency/insufficiency increased the odds of developing COVID-19 (OR 1∙46, 95% CI 1∙28–1∙65, p<0∙0001, I  ²=92%), severe disease (OR 1∙90, 95% CI 1∙52–2∙38, p<0.0001, I  ²=81%) and death (OR 2∙07, 95% CI 1∙28–3∙35, p=0.003, I  ²=73%). 25-hydroxy vitamin D (25(OH)D) concentration were lower in individuals with COVID-19 compared to controls (mean difference [MD] -3∙85 ng/mL, 95% CI -5∙44,-2∙26, p=<0.0001), in patients with severe COVID-19 compared to controls with non-severe COVID19 (MD -4∙84 ng/mL, 95% CI -7∙32,-2∙35, p=0∙0001) and in non-survivors compared to survivors (MD -4∙80 ng/mL, 95%-CI -7∙89,-1∙71, p=0∙002). The association between vitamin D deficiency/insufficiency and death was insignificant when studies with high risk of bias or studies reporting unadjusted effect estimates were excluded. Risk of bias and heterogeneity were high across all analyses. Discrepancies in timing of vitamin D testing, definitions of severe COVID-19 and vitamin D deficiency/insufficiency partly explained the heterogeneity. Four RCTs were widely heterogeneous precluding meta-analysis.

Conclusion

Multiple observational studies involving nearly two million adults suggest vitamin D deficiency/insufficiency increases susceptibility to COVID-19 and severe COVID-19, although with a high risk of bias and heterogeneity. Association with mortality was less robust. Heterogeneity in RCTs precluded their meta-analysis.