Covid-19 pandemic and vitamin d deficiency: A different approach with an analysis of the findings and a complimentary proposal

Vitamin D is an essential immune-modulator with receptors widely distributed throughout the body, and its serum levels fluctuate significantly in individuals between winter and summer months. This study examines the association between low vitamin D status and prevalence of COVID-19 cases around the world and proposes a relationship with the seasonal character of the human immune system strength rather than to the seasonal infectivity of viruses. Also, this review suggests that the observed geographical disparities in COVID-19 cases are due to differences in vitamin D levels. On the international scale, serum vitamin D levels are reportedly lowest in China, the Middle East, and South Europe; these populations also had the largest outbreaks of COVID-19 cases. In addition to the geographical differences in vitamin D status, there are known risk groups (ethnic, age-related, pregnancies). In contrast, some countries including Canada, Finland, and North Europe incorporate increased amounts of vitamin D through fortified foods, vitamin D supplements, and sunbathing. These countries show the lowest morbidity and mortality rates by COVID-19 infection and demonstrate that lower ambient temperatures do not contribute to a higher number of COVID-19 cases. COVID-19 has spread around the globe almost simultaneously in both warm and cold areas. Given this information, vitamin D measurement should become an essential component of public health monitoring as a biomarker of immunity status. Clinical trials should be conducted to confirm this hypothesis. COVID-19 tests should be performed together with vitamin D status tests to verify this proposed relationship.