"There are a growing number of data suggesting the link between serum 25(OH)D concentrations and COVID-19 infectivity and severity. Although the results from randomized clinical trials aiming to prove the benefit of vitamin D supplementation for these purposes are pending, there is no downside to increasing vitamin D intake and having sensible sunlight exposure to maintain serum 25(OH)D at a level of at least 30 ng/mL (75 nmol/L) and preferably at 40 to 60 ng/mL (100-150 nmol/L) to achieve optimal health benefits of vitamin D and minimize the risk of COVID-19 infection and its severity."

Source: https://www.endocrinepractice.org/article/S1530-891X(21)00087-2/fulltext