Vitamin D and COVID-19: A Physiological Perspective

Already known to be capable of enhancing the performance of the immune system, preclude microbial infections, and reduce susceptibility to influenza, Vitamin D, or 1,25-dihydroxyvitamin D (1,25(OH)2D) as an active form, it has maintained a positive reputation in discourses regarding COVID-19 for a lengthy amount of time. Its deficiency is statistically correlated with infection of the disease, the severity thereof, and fatalities therefrom. There have also existed suggestions that Vitamin D supplements could either prevent contracting SARS-CoV-2, the Coronavirus that causes the disease, or alleviate the symptoms it is capable of begetting, since data has established a relationship between Vitamin D supplementation and the severity of respiratory illnesses and certain assays indicated optimistic results in COVID-19 patients supplemented with the vitamin. Accordingly, a great deal of research and efforts have been put into investigating the physiological mechanisms in the human body attributable to the vitamin's reputation against the Coronavirus and combined with what was already discovered before the advent of SARS-CoV-2, a great amount of knowledge has consequently been unveiled. Via regulation of various pathways, 1,25(OH)2D promotes the production of antimicrobial peptides, autophagy, the integrity and impermeability of cellular junctions against pathogens, as well as mitigate the consequences of SARS-CoV-2 infection such as cytokine storm through immunomodulation of the T cell differentiation pathways and lung injury through stimulation of the Angiotensin-Converting Enzyme 2 (ACE2) and manipulation of the Renin-Angiotensin System (RAS). Nevertheless, the unfortunate fact is that Vitamin D deficiency still plagues the global population across all age categories, which could have translated into humanity's heightened exposure to the Coronavirus. With the COVID-19 pandemic inexorably raging on with no prospect of termination observable in the foreseeable future, this review article provides a concise yet thorough insight into that vast knowledge, which could illuminate the significance of Vitamin D amidst the current predicament experienced by mankind, as well as instigate more curiosity as to any current unclarity related to the issue and ignite further discussions and studies that would deliver more understanding to the vitamin's role as a safeguard against SARS-CoV-2