Low vitamin D levels may increase risk for coronavirus, according to a new study from medical and social science researchers at the University of Chicago.

The study, published Sept. 3 in JAMA Network Open, was based on a cohort of 489 patients who had their vitamin D level measured at a major academic center in the year before COVID-19 testing began. Fifteen percent later tested positive for COVID-19.

Researchers determined that the relative risk of testing positive for COVID-19 was 1.77 times greater for patients with a deficiency of the vitamin compared with those who had a sufficient supply.

This week, researchers presenting at the European Society of Endocrinology also linked low vitamin D levels to a range of other conditions from cardiovascular disease to cancer, but they argued that risk association should be made according to a specific measurement.

Their data suggest that the free, precursor form of vitamin D found circulating in the bloodstream is a more accurate predictor of future health and disease risk than the more often-measured total vitamin D.

More than 99% of all vitamin D metabolites in human blood are bound to proteins, with the rest free to be “biologically active.” In the new study, only free 25-hydroxyvitamin D was predictive of future health problems and not free 1,25-dihydroxyvitamin D.

“These data further confirm that vitamin D deficiency is associated with a negative impact on general health and can be predictive of a higher risk of death,” said author Leen Antonio, M.D., Ph.D., of University Hospitals Leuven in Belgium.

The JAMA study linking Vitamin D to COVD-19 risk used readings of 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol levels. Its authors called for additional randomized clinical trials to determine whether Vitamin D interventions can reduce COVID-19 incidence either in the broad population or among targeted groups at increased risk.

“Since African American and Hispanic populations in the U.S. have both high rates of vitamin D deficiency and bear a disproportionate burden of morbidity and mortality from COVID-19, they may be particularly important populations to engage in studies of whether vitamin D can reduce the incidence and burden of COVID-19,” the researchers wrote. “Testing of vitamin D levels may be an important tool in guiding treatments, and the availability of low-cost home testing for vitamin D may be valuable given the benefits of social distancing in COVID-19.”