Interest in using Vitamin D to prevent or treat acute respiratory infections dates back to the 1930s when people tried cod liver oil to prevent the common cold (the virus that causes the cold includes a type of coronavirus). People who are at risk for severe COVID-19 (due to obesity, older age, and Black or Asian ethnic origin) often have low Vitamin D levels, which suggests that Vitamin D may help prevent COVID-19. In Europe, severe COVID-19 infections are common in populations with low levels of Vitamin D . It makes sense to encourage people to get enough Vitamin D, either from sunlight, which helps make Vitamin D, or foods such as fatty fish (salmon, tuna and mackerel); cheese; mushrooms; and egg yolks. There is a chance that this might reduce the impact of COVID-19 in populations without enough Vitamin D. There is nothing to lose by adding in these things, and potentially much to gain.