Countries with higher death rates had larger numbers of people with vitamin D deficiency than countries with lower death rates.
— Read on www.webmd.com/lung/news/20200518/more-vitamin-d-lower-risk-of-severe-covid-19
In the northern hemisphere, people are more likely to be lower in Vitamin D because of the shorter days and the position the earth is relative to the sun. Supplementation could be a good idea if it’s not realistic to increase Vitamin D consumption by being in the sun or from food sources. Nevertheless, Vitamin D has not been shown to prevent COVID-19.