In a fight against the COVID-19 pandemic, new research adds to the growing body of evidence that vitamin D deficiency may raise the risk of getting novel coronavirus.

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Vitamin D is a hormone, produced in the skin during exposure to sunlight, and helps regulate the amount of calcium and phosphate in the body, which are needed to keep bones, teeth and muscles healthy. In a retrospective study of patients tested for COVID-19, published in the journal JAMA Network Open, the researchers found an association between vitamin D deficiency and the likelihood of becoming infected with the coronavirus.

"Vitamin D is important to the function of the immune system and vitamin D supplements have previously been shown to lower the risk of viral respiratory tract infections," said study lead author David Meltzer from the University of Chicago (UChicago) in the US. "Our statistical analysis suggests this may be true for the COVID-19 infection," Meltzer added.

For the study, the research team looked at 489 UChicago Medicine patients whose vitamin D level was measured within a year before being tested for COVID-19. The findings showed that patients who had vitamin D deficiency, that was not treated, were almost twice as likely to test positive for the COVID-19 coronavirus compared to patients who had sufficient levels of the vitamin. "Half of Americans are deficient in Vitamin D, with much higher rates seen in African Americans, Hispanics and individuals living in areas like Chicago where it is difficult to get enough sun exposure in winter," the researchers wrote. "Understanding whether treating Vitamin D deficiency changes COVID-19 risk could be of great importance locally, nationally and globally," Meltzer said.

Vitamin D is inexpensive, generally very safe to take, and can be widely scaled. The research team emphasized the importance of experimental studies to determine whether vitamin D supplementation can reduce the risk, and potential severity, of COVID-19. They also highlight the need for studies of what strategies for vitamin D supplementation may be most appropriate in specific populations. They have initiated several clinical trials at UChicago Medicine and with partners locally. Earlier, another study published in the journal FEBS, found that low levels of Vitamin D in the blood are associated with an increased risk of COVID-19 infection.