"Let’s consider some of the evidence for vitamin D and CO....:
A meta-analysis of 25 randomized controlled trials showed that vitamin D supplementation significantly reduces the risk of acute respiratory infections in the overall population by 12% and in those with profound vitamin D deficiency by 70%.
Fifteen studies have compared survival rates between groups with higher and lower vitamin D levels, and consistently show that people with higher levels of vitamin D do better, especially compared with those who are deficient, which describes 42 percent of the US population. The findings of these fifteen studies clearly contradict the two negative studies referenced above.
It is well known that vitamin D is critical to the immune system. It activates the immune system’s defenses, enhances the function of T cells and macrophages against pathogens, and is critical to the production of cathelicidin, an antimicrobial peptide."
Source, full article with some recommendations: https://anh-usa.org/is-vitamin-d-a-covid-bust/