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Patients with "likely deficient" vitamin D status had nearly doubled risk of testing positive for COVID-19 versus those with "likely sufficient" vitamin D, a single-center study found.

Among nearly 500 patients, the relative risk for infection was 1.77 (95% CI 1.12-2.81, P=0.02) in those judged to be vitamin D-deficient (below 20 ng/mL or 18 pg/mL, respectively) compared with patients believed to have sufficient vitamin D, reported David Meltzer, MD, PhD, of the University of Chicago, and colleagues writing in .

Deficiency and sufficiency were estimated not only on the basis of vitamin D metabolite levels (25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol with thresholds of 20 ng/dL and 18 pg/mL, respectively) but also on records of vitamin D supplement prescriptions following those measurements.

The authors acknowledged one major caveat, however: vitamin D deficiency may be associated with many other COVID-19 risk factors, including age, obesity, diabetes, and chronic illness. Their statistical analysis included adjustments for many of these, but potential remained for residual confounding.

"[O]bserved associations of vitamin D with outcomes in almost any observational study may fail to accurately reflect any potential causal effects of vitamin D on outcomes," they cautioned.

The authors pointed to prior research suggesting a link between vitamin D and a decrease in other viral respiratory infections, and also noted vitamin D deficiency is "common." In particular, they cited the potential of shelter-in-place orders to decrease sun exposure, augmenting the need for vitamin D supplementation.

"To our knowledge, this study provides the first assessment of the association of vitamin D deficiency and potentially insufficient treatment with testing positive for COVID-19," they wrote.

Meltzer and colleagues drew on electronic health record data from 4,314 patients tested for COVID-19 at their institution from March 3 to April 10. Of these, 489 had complete data and were included in the sample. Average patient age was 49, 75% were women, and almost 70% were nonwhite (primarily Black).

One-quarter were determined to be likely deficient in vitamin D and 59% were likely sufficient; the remainder didn't qualify for either status because supplement prescriptions after measurement introduced uncertainty.

Compared to patients who weren't vitamin D deficient, those who were tended to be younger, a race other than white, more likely to receive vitamin D2 and less likely to receive vitamin D3.

Overall, 71 participants tested positive for COVID-19.

Other than vitamin D deficiency being a consequence of chronic health conditions or behavioral factors that increase COVID-19 risk, limitations to the data also include its limited sample size and that researchers were limited to data within the electronic health record.

Meltzer and colleagues suggested that interventions to reduce vitamin D deficiency, as a means to reduce COVID-19 risk, be tested in randomized trials. Such research would be especially pertinent since both African-American and Hispanic populations not only have disproportionate morbidity and mortality from COVID-19, but also high rates of vitamin D deficiency.

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