ABSTRACT
BACKGROUND AND OBJECTIVE: Hypovitaminosis D has been proposed as a risk factor for increased susceptibility to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and severe outcomes in coronavirus disease 2019 (COVID-19). Likewise, vitamin D supplementation has been proposed as an effective means for preventing and improving clinical outcomes in COVID-19. Nevertheless, available data are markedly inconsistent and contradictory. Considering the heterogeneity in the available clinical evidence, we planned to undertake a narrative review and provide a precise summary of the role of vitamin D in COVID-19. METHODS: PubMed/MEDLINE database was searched from inception till September 30, 2023 using appropriate MeSH terms. The initial search revealed 900 results. Thereafter, titles and abstracts were scanned and commentaries, letters, and editorials were excluded. Relevant observational studies and clinical trials/randomized controlled trials (RCTs) were full-text assessed and pertinent data were extracted for this narrative review. KEY CONTENT AND FINDINGS: Data from observational and ecological studies suggest that hypovitaminosis D is associated with a higher risk of acquiring COVID-19. Similarly, evidence support a negative association between 25-hydroxyvitamin D levels and COVID-19 severity, nevertheless, causality remains to be established. With regard to vitamin D supplementation and COVID-19-related health outcomes, data from observational studies and RCTs are contradictory. Even in moderate-to-severe/severe COVID-19, vitamin D supplementation has not been shown to be beneficial. Besides, data suggest that vitamin D levels might alter COVID-19 vaccine efficacy and be associated with long COVID. CONCLUSIONS: Vitamin D deficiency is linked to an increased risk of acquiring SARS-CoV-2 infection and poor COVID-19 prognosis, however, available evidence with regard to improved clinical outcomes with vitamin D supplementation is inconsistent.
