One major micronutrient studied for its possible protective effect against the COVID-19 disease is vitamin D. This systematic review sought to identify and synthesize available evidence to aid the understanding of the possible effect of vitamin D deficiency on COVID-19 status and health outcomes in COVID-19 patients. Three databases (PubMed, ScienceDirect, and Google Scholar) were systematically used to obtain English language journal articles published between 1 December 2019 and 3 November 2020. The search consisted of the terms (“Vitamin D,” OR “25-Hydroxyvitamin D,” OR “Low vitamin D.”) AND (“COVID-19” OR “2019-nCoV” OR “Coronavirus” OR “SARS-CoV-2”) AND (“disease severity” OR “IMV” OR “ICU admission” OR “mortality” OR “hospitalization” OR “infection”). We followed the recommended PRISMA guidelines in executing this study. After going through the screening of the articles, eleven articles were included in the review. All the included studies reported a positive association between vitamin D sufficiency and improved COVID-19 disease outcomes. On the other hand, vitamin D deficiency was associated with poor COVID-19 disease outcomes. Specifically, two studies found that vitamin D-deficient patients were more likely to die from COVID-19 compared to vitamin D-sufficient patients. Three studies showed that vitamin D-deficient people were more likely to develop severe COVID-19 disease compared to vitamin D-sufficient people. Furthermore, six studies found that vitamin D-deficient people were more likely to be COVID-19 infected compared to vitamin D-sufficient people. Findings from these studies suggest that vitamin D may serve as a mitigating effect for COVID-19 infection, severity, and mortality. The current evidence supports the recommendations for people to eat foods rich in vitamin D such as fish, red meat, liver, and egg yolks. The evidence also supports the provision of vitamin D supplements to individuals with COVID-19 disease and those at risk of COVID-19 infection in order to boost their immunity and improve health outcomes.
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