Higher levels of vitamin D than traditionally considered sufficient may help prevent COVID-19 infection — particularly in Black patients, shows a new single-center, retrospective study looking at the role of vitamin D in prevention of infection.

The study, published recently in JAMA Network Open, notes that expert opinion varies as to what “sufficient” levels of vitamin D are, some define this as 30 ng/mL, while others cite 40 ng/mL or greater.

In their discussion, the authors also note that their results show: “Risk of positive COVID-19 test results decreased significantly with increased vitamin D level of 30 ng/mL or greater when measured as a continuous variable.”

“These new results tell us that having vitamin D levels above those normally considered sufficient is associated with decreased risk of testing positive for COVID-19, at least in Black individuals,” said lead author, David Meltzer, MD, chief of hospital medicine at University of Chicago Medicine in Illinois, in a press release from his institution.

“These findings suggest that randomized clinical trials to determine whether increasing vitamin D levels to greater than 30 to 40 ng/mL affect COVID-19 risk are warranted, especially in Black individuals,” he and his coauthors say.

Vit D at Time of Testing Most Strongly Associated With COVID Risk

An earlier study by the same researchers found that vitamin D deficiency (less than 20 ng/ml) may raise the risk of testing positive for COVID-19 in people from various ethnicities, as reported by Medscape.

Data for this latest study were drawn from electronic health records for 4638 individuals at the University of Chicago Medicine and were used to examine whether the likelihood of a positive COVID-19 test was associated with a person’s most recent vitamin D level (within the previous year), and whether there was any effect of ethnicity on this outcome.

Mean age was 52.8 years; 69% were women; 49% were Black; 43% white; and 8% were another race/ethnicity.

A total of 27% of the individuals were deficient in vitamin D (less than 20 ng/mL), 27% had insufficient levels (20 to less than 30 ng/mL), 22% had sufficient levels (30 to less than 40 ng/mL), and the remaining 24% had levels of 40 ng/mL or greater.

In total, 333 (7%) of people tested positive for COVID-19, including 102 (5%) whites and 211 (9%) Blacks. And 36% of Black individuals who tested positive for COVID-19 were classified as vitamin D deficient, compared with 16% of whites.

A positive test result for COVID-19 was not significantly associated with vitamin D levels in white individuals but was in Black individuals.

So in Black people, compared with levels of ≥ 40 ng/mL, vitamin D levels of 30 to < 40 ng/mL were associated with an incidence rate ratio (IRR) of 2.64 for COVID-19 positivity (P = 0.01). For levels of 20 to < 30 ng/mL, the IRR was 1.69 (P = 0.21); and for < 20 ng/mL the IRR was 2.55 (P = .009).

The researchers also found that the risk of positive test results with lower vitamin D levels increased when those levels were lower just prior to the positive COVID-19 test, lending “support [to] the idea that vitamin D level at the time of testing is most strongly associated with COVID-19 risk,” they write.

Try Upping Vitamin D Levels to 40 ng/mL or Greater to Prevent COVID?

In their discussion, the authors note that significant association of vitamin D levels with COVID-19 risk in Blacks but not in whites, “could reflect their higher COVID-19 risk, to which socioeconomic factors and structural inequities clearly contribute.”

“Biological susceptibility to vitamin D deficiency may also be less frequent in white than Black individuals, since lighter skin increases vitamin D production in response to sunlight, and vitamin D binding proteins may vary by race and affect vitamin D bioavailability.”

Given less than 10% of US adults have a vitamin D level greater than 40 ng/mL, the study findings increase the urgency to consider whether increased sun exposure or supplementation could reduce COVID-19 risk, according to the authors.

“‘When increased sun exposure is impractical, achieving vitamin D levels of 40 ng/mL or greater typically requires greater supplementation than currently recommended for most individuals of 600-800 IU/d vitamin D3,” they add.

However, Meltzer also acknowledges, “This is an observational study. We can see that there’s an association between vitamin D levels and likelihood of a COVID-19 diagnosis, but we don’t know exactly why that is, or whether these results are due to the vitamin D directly or other related biological factors.”

All in all, the authors suggest that randomized clinical trials are needed to understand if vitamin D can reduce COVID-19 risk, and as such they should include doses of supplements likely to increase vitamin D to at least 40 ng/mL, and perhaps even higher, although they point out that the latter must be achieved safely.

“Studies should also consider the role of vitamin D testing, loading doses, dose adjustments for individuals who are obese or overweight, risks for hypercalcemia, and strategies to monitor for and mitigate hypercalcemia, and that non-white populations, such as Black individuals, may have greater needs for supplementation,” they outline.

They are now recruiting participants for two separate clinical trials testing the efficacy of vitamin D supplements for preventing COVID-19.

The authors have disclosed no relevant financial relationships.

JAMA Netw Open. 2021;4:e214117. Full text