Studies show low vitamin D levels are associated with higher risks of contracting COVID-19 or with becoming seriously ill

In a retrospective study of patients tested for COVID-19, researchers at the University of Chicago Medicine 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 David Meltzer, MD, PhD, Chief of Hospital Medicine at UChicago Medicine and lead author of the study. “Our statistical analysis suggests this may be true for the COVID-19 infection.”

The research team looked at 489 UChicago Medicine patients whose vitamin D level was measured within a year before being tested for COVID-19. Patients who had vitamin D deficiency (< 20ng/ml) that were not treated were almost twice as likely to test positive for the COVID-19 coronavirus than patients who had sufficient levels of the vitamin.

The study, “Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results,” was published Sept. 3 in JAMA Network Open. Findings were previously reported on medRxiv, a preprint server for the health sciences.

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.

“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.”

Meltzer and his team emphasize 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 on 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.

Among recent studies finding a link between vitamin D levels and how severe COVID-19 is:

Researchers from the U.K. evaluated the average vitamin D levels and the number of COVID-19 cases and the death rates across 20 European countries. Countries with low average vitamin D blood levels in the population had higher numbers of COVID-19 cases and deaths, says study leader Petre Cristian Ilie, MD, PhD, research and innovation director at the Queen Elizabeth Hospital Foundation Trust in King’s Lynn, U.K.

At Northwestern University, researchers used modelling to estimate that 17% of those deficient in vitamin D would develop a severe COVID-19 infection, but only about 14% of those with healthy vitamin D levels. They estimated the association between vitamin D and severe COVID-19 based on a potential link between vitamin D deficiency and C-reactive proteins, or CRP, a surrogate marker for severe COVID-19

In a small study, Louisiana and Texas researchers evaluated 20 patients hospitalized with COVID-19, finding that 11 of the patients admitted to the ICU were vitamin D deficient. Still, only four of those did not need the ICU.

Indonesian researchers evaluated 780 documented cases of COVID-19 and found that most patients who died had vitamin D levels below normal.

Irish researchers analyzed European population studies and vitamin D levels, finding countries with high rates of vitamin D deficiency also had higher death rates from COVID-19. Those researchers asked the government to raise the vitamin D recommendations.