Vitamin D in patients with COVID-19: is there a room for it?

Vitamin-D receptors are found in a variety of cells with the potential to regulate many cellular functions. Higher COVID-19 severity has been reported in individuals, which are known to have lower vitamin-D levels. The relation between vitamin-D and COVID-19 has been analysed with a number of studies but only few met high standards. Studies revealed discordant findings. There is no data from interventional trials clearly indicating that vitamin-D supplementation may prevent against COVID-19. An increasing number of observational studies put forward the preventive feature of adequate vitamin-D status for COVID-19 mortality. Yet, there are again conflicting findings. This narrative review summarizes the current evidence and provides a practical advice to lessen the impact of COVID-19 by ensuring recommended vitamin-D intakes. This approach would not be harmful, but potentially useful. Vitamin-D is safe especially if it does not exceed the upper-tolerable-limit. Daily doses are recommended over the weekly or monthly higher doses. Mega-doses are not recommended because of its potential to lead adverse events. The target level of vitamin-D is proposed above 30 ng/mL in majority of the studies. Nonetheless, one should consider that the benefit is foreseen to be small, and some time (months) may be needed for such effect.