Vitamin D deficiency is less common in countries where the sun exposure is consistent throughout the year or where the use of vitamin D fortified food is widespread. Various authors suggested that vitamin D deficiency might play a role in the variability of COVID-19 impact on different countries [175,176,177,181]. Ilie and colleagues searched literature for mean vitamin D level in each country and observed a negative correlation between vitamin D levels and number of COVID-19 cases and deaths [181]. Ali described a significant negative correlation between mean vitamin D levels and COVID-19 cases per one million population in European countries, as of 20 May 2020 [182].