Study participants who had vitamin D deficiency were almost twice as likely to test positive for the COVID-19 coronavirus compared to patients who had sufficient levels of the vitamin.

In this study published in JAMA Network Open, researchers at the University of Chicago Medicine found an association between vitamin D deficiency and the likelihood of becoming infected with the coronavirus. The study included 489 patients. Their vitamin D level was measured within a year before being tested for COVID-19.

“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,” David Meltzer, MD, PhD, Chief of Hospital Medicine and lead author of the study, told media outlets. “Our statistical analysis suggests this may be true for the COVID-19 infection.”

Half of Americans are deficient in Vitamin D; yet, higher rates occur among African Americans, Hispanics, and individuals living in areas like Chicago where it is difficult to get enough sun exposure in winter.

A disproportionate percentage of COVID-19 cases and deaths are occurring among Blacks, Native Americans, Hispanic, and Latino people. Rates for these groups range from about 4.7 to 5.3 times those of non-Hispanic white people.

Societal factors—underlying health conditions, dense living conditions, employment in the service industry or as an essential worker, acess to health care, discriminatory treatment—all may contribute to the impact of COVID-19 on people of color, who are often more greatly affected by any public health emergencies, such as hurricane Katrina.

“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.”