Vitamin A Nutritional Status and Clinical Outcomes in COVID-19: A Systematic Review.

The role of vitamin A in the pathophysiological context of coronavirus disease 2019 (COVID-19) represents a current challenge, given the major impact of COVID-19 on morbidity and mortality and the importance of retinol in pulmonary and immunomodulatory functions. The aim of this review is to assess the relationship between vitamin A nutritional status and clinical outcomes in people with COVID-19. The PubMed, Web of Science, Scopus and ScienceDirect databases were used to search for observational studies that assessed retinol levels in hospitalized individuals with COVID-19, following the PRISMA recommendations. A total of 1,912 articles were identified and seven met the inclusion criteria. Four studies showed borderline or deficient retinol blood levels (retinol <0.20 mg/L or <0.70 mol/L) in people with COVID-19, associated with worsened clinical outcomes. In the other three studies lower mean values of this vitamin were identified in COVID-19 symptomatic groups compared to asymptomatic or convalescent groups that showed worse clinical outcomes. The results suggest a possible association between retinol and COVID-19 outcomes. However, there is a clear need to develop clinical trials to elucidate the role of vitamin A in the pathophysiological process of COVID-19.