Analysis of the increase in COVID-19 cases in European countries, showing no correlation with temperature, but a significant correlation with country latitude. Since UV radiation decreases earlier for higher latitudes, this supports the theory that low vitamin D levels increases COVID-19 risk.
Author recommends that vitamin D supplementation be considered to reduce pandemic severity during the winter, noting that UV levels in Europe and Northern USA will not return to a level above that of October until the end of March.
Walrand et al., 1/21/2021, peer-reviewed, 1 author.