Researchers from three Korean hospitals have found that vitamin D deficiency has a major impact on causing and aggravating Covid-19 and how it does so.

Vitamin D is a nutrient that greatly affects the activities of the innate and acquired immune systems, including various immune responses in the body. Several Korean and foreign researchers have reported that vitamin D has had a close relationship with the infection rate and severity of Covid-19 since the early days of the pandemic.

The joint research team revealed the role and mechanism of vitamin D in Covid-19. As a result, the team confirmed that the lower the vitamin D concentration in the blood, the higher the risk and severity of Covid-19.

However, when patients supplemented their low vitamin D intake, the positive rate of Covid-19 virus, the causative virus of Covid-19, the rate of admission to the intensive care unit, and mortality rate in patients with moderate or higher severity decreased.

Professors Lim Soo at Seoul National University Bundang Hospital and Bae Jae-hyun at Korea University Anam Hospital, and Bae Jae-hyun of Seoul National University Hospital wrote the review paper after examining all existing studies.

The research team pointed to abnormalities in the immune system and the inflammatory response system as the most direct cause of this pattern.

Vitamin D deficiency causes decreased production of antimicrobial peptides, the abnormal immune response of T cells, increased apoptosis of lung epithelial cells and increased secretion of inflammatory cytokines from immune cells. As a result, it lowers the body's immunity making it more susceptible to infection with Covid-19 while increasing the risk of a cytokine storm, which is fatal to severely ill patients.

The researchers also confirmed that low vitamin D concentrations had increased severity while adversely affecting cardiovascular and metabolic diseases such as heart disease and diabetes.

According to the paper, vitamin D deficiency lowers the blood pressure control system renin-angiotensin-aldosterone system (RAAS) and glucose metabolism, exacerbating underlying diseases such as diabetes, thereby increasing the fatality rate.

"This study is meaningful, proving that vitamin D deficiency has an association with susceptibility and severity to Covid-19," Professor Bae said. "Although the degree is not large, vitamin D supplementation to patients with vitamin D deficiency has a good effect on various respiratory infections, including Covid-19."

Professor Lim also said, "While there are currently no agreed guidelines for blood vitamin D levels in Covid-19 patients, it is clear that vitamin D deficiency has an adverse effect on the course of Covid-19."

Lim added that he recommended that people avoid developing vitamin D deficiency during the pandemic and maintain a vitamin D blood concentration above 30 ng/mL.

Reviews in Endocrine and Metabolic Disorders published the study results in its latest issue.