COVID-19; respiratory infection; retinoic acid; retinol; alpha-tocopherol.
COVID-19 is a disease caused by SARS-CoV-2, a new coronavirus first identified in Wuhan (China) and rapidly spread throughout the world that affects the immune system causing exacerbated inflammation. Viral infections can lead to the depletion of levels of some vitamins, such as vitamins A and E, and inadequate nutrient levels can be harmful to health. This study aims to investigate whether COVID-19 affects levels of these vitamins and how they can help fight infection. Two studies were carried out: an experimental study and a systematic review. The systematic review was performed according to the PRISMA declaration, using three different databases. Data from articles were collected and analyzed by two independent researchers. The quality of in vivo studies was also evaluated. We identified 4,572 articles, of which 10 met the inclusion criteria. Three of them were related to vitamin A, two to vitamin E, and five related both vitamins to COVID-19. The cross-sectional study was conducted between May and October 2020. Clinical data were collected by face-to-face interviews or by telephone contact and by access to the medical records of hospitalized patients. Participants were allocated into two groups according to severity, with a group of mild (n = 88) or critical (n = 106) patients and a control group (n = 46). The data were transferred to the Research Electronic Data Capture (Redcap, Vanderbilt University) and analyzed by the Statistical Package for the Social Sciences (IBM SPSS Statistics 26). P values <0.05 were considered statistically significant. Patients with COVID-19 presented a reduction in vitamin A and E concentrations, being below or close to the reference values for deficiency. Supplementation of these vitamins was associated with a better prognosis (p<0.001). Low vitamin A levels (<0.7 mmol/L) were associated with higher chances of persistent symptoms after 90 days. Experimental studies have shown that these vitamins can be targets against SARS-CoV-2 infection and the retinoic acid-inducible I gene (RIG-I) plays an important role in combating the disease through different mechanisms. However, the therapeutic capacity of these vitamins requires additional biological validation through more robust studies, such as randomized clinical trials and the evaluation of the food intake of these vitamins. In addition, studies are also needed to assess serum levels of these vitamins before infection.