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People who are deficient in vitamin D may be at higher risk of contracting the novel coronavirus than those with sufficient levels, according to the results of a new retrospective study from Illinois.

Individuals with untreated vitamin D deficiency were nearly twice as likely to test positive for COVID-19 relative to their peers with adequate vitamin D levels.

“These findings appear to support a role of vitamin D status in COVID-19 risk,” the authors say in the study, published online September 3 in JAMA Network Open.

“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. Our statistical analysis suggests this may be true for the COVID-19 infection,” lead author David Meltzer, MD, PhD, chief of hospital medicine at University of Chicago Medicine, Illinois, said in a news release from his institution.

Important for Immune Function

Meltzer and colleagues studied 489 University of Chicago Medicine patients (mean age 49 years, 75% women) whose vitamin D levels were determined in the 2 months before being tested for COVID-19.

Vitamin D deficiency was defined as < 20 ng/mL 25-hydroxycholecalciferol or < 18 pg/mL 1,25-dihydroxycholecalciferol.

Vitamin D status was categorized as likely deficient for 124 participants (25%), likely sufficient for 287 (59%), and uncertain for 78 (16%).

A total of 71 participants (15%) tested positive for COVID-19.

In a multivariate analysis, a positive COVID-19 test was significantly more likely in those with likely vitamin D deficiency than in those with likely sufficient vitamin D levels at the time of COVID-19 testing (relative risk [RR], 1.77; 95% CI, 1.12 – 2.81; = .02).

The estimated mean rate of COVID-19 in the deficient group was 21.6% compared with 12.2% in the sufficient group.

Testing positive for COVID-19 was also associated with increasing age up to age 50 years (RR, 1.06; P = .02) and race other than White (RR, 2.54; P = .009)

Protective Effect of Treatment?

The findings also raise the possibility that treatment for vitamin D deficiency may lower the risk of COVID-19, the researchers say.

Patients with deficient vitamin D levels who had their vitamin D treatment increased did not appear to have increased risk for COVID-19.

This suggests a “protective effect of treatment, but the confidence intervals on estimated rates for these groups are too wide to exclude the possibility of no treatment effect,” Meltzer and colleagues note.

“If vitamin D does reduce COVID-19 incidence, it is tempting to consider whether it might reduce COVID-19 transmission,” they hypothesize.

Because vitamin D strengthens innate immunity it could be expected to decrease COVID-19 infection and transmission. Vitamin D also affects zinc metabolism, which decreases the replication of coronaviruses.

As previously reported by Medscape Medical News, a recent study from Israel suggested low plasma vitamin D levels are an independent risk factor for COVID-19 infection and hospitalization.

In that study, participants positive for COVID-19 were 50% more likely to have low vs normal vitamin D levels in a multivariate analysis that controlled for other confounders.

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 colleagues say randomized clinical trials are now needed to see whether broad population interventions and interventions among groups at increased risk of vitamin D deficiency and COVID-19 could reduce COVID-19 cases.

The study was supported by the Learning Health Care System Core of the University of Chicago/Rush University Institute for Translational Medicine (ITM) Clinical and Translational Science Award and the African American Cardiovascular Pharmacogenetics Consortium. The authors have declared no relevant conflicts of interest.

JAMA Netw Open. Published September 3, 2020. Full text