COVID-19: High Vitamin D Levels May Protect Black People
Vitamin D plays a wide range of roles in the body, including regulating calcium levels, maintaining healthy bones and teeth, and supporting the immune system.
In addition to getting vitamin D from dietary sources, the body can make its own in the skin through exposure to sunlight.
However, it can be difficult for people with dark skin and those with low exposure to sunlight to maintain sufficiently high levels of the vitamin, especially during the winter months.
One study found that, overall, about 42% of people in the United States were deficient in vitamin D. The figure rose to 82% among Black people and 70% among Hispanic people.
Accumulating evidence has shown that people with deficient vitamin D levels are more likely to test positive for SARS-CoV-2, which is the virus that causes COVID-19. They may also be more likely to develop severe disease.
This association may partly explain why the pandemic has disproportionately affected Black, Hispanic, and other non-white populations.
Clinical trials have found that vitamin D supplements can help protect people against other respiratory infections resulting from viruses.
The research suggests that taking a vitamin D supplement can even reduce viral infections among people who are not deficient in the vitamin, based on the recommended intake in the current guidelines. These recommendations are based on the levels necessary to maintain healthy bones.
Dr. David Meltzer, Ph.D., and his colleagues at the University of Chicago, IL, wondered whether the same could be true of vitamin D and COVID-19.
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Vitamin D blood tests
The researchers analyzed the medical records of 4,638 individuals who had a vitamin D blood test in the 12 months before having a PCR test for SARS-CoV-2 at the University of Chicago Medical Center (UChicago Medicine).
The researchers used the length of time since the vitamin D test and subsequent treatments to estimate the participantsâ€™ vitamin D levels 14 days before the PCR test.
In addition, they accounted for factors that are known to increase a personâ€™s risk of COVID-19, such as age, sex, race, and medical conditions.
In total, 211 Black participants and 102 white participants tested positive for SARS-CoV-2.
The researchers discovered that among Black participants, the risk of testing positive was 2.64 times as high for those with a serum vitamin D level of 30â€“ 39.9 nanograms per milliliter (ng/ml) â€” a â€œsufficientâ€ level â€” as it was for those with a level of at least 40 ng/ml.
In other words, there appeared to be a significant protective effect from having levels above the range that experts consider to be sufficient.
Among Black participants with a vitamin D level of at least 30 ng/ml, every incremental 1 ng/ml increase in the level of the vitamin led to a 5% decrease in the risk of testing positive for SARS-CoV-2.
â€œThis supports arguments for designing clinical trials that can test whether or not vitamin D may be a viable intervention to lower the risk of the disease, especially in Persons of Color,â€ he adds.
There were no statistically significant associations between vitamin D levels and the risk of testing positive for SARS-CoV-2 among white individuals.
The researchers attribute this to the relatively low number of positive SARS- CoV-2 tests among white people in their sample.
Similarly, the numbers of participants from other racial groups, including Hispanic people, were too small to yield statistically significant results.
The study appears in the journal JAMA Network Open.
Case for high dose supplements
â€œThese results increase the urgency to consider whether increased sun exposure or vitamin D supplementation could reduce COVID-19 risk,â€ say the researchers in their paper.
They write that less than 5â€“10% of adults in the U.S. are likely to have vitamin D levels greater than 40 ng/ml. To attain these levels from taking a supplement â€” without increased sun exposure â€” would require more than the currently recommended daily dose.
â€œLifeguards, surfers; those are the kinds of folks who tend to have more than sufficient vitamin D levels,â€ says Dr. Meltzer. â€œMost folks living in Chicago in the winter are going to have levels that are well below that.â€
The National Institutes of Health (NIH) recommend 600 international units (IU), which equates to 15 micrograms (mcg), daily for adults aged 19â€“70 years. For adults aged 71 years and older, the recommended amount rises to 800 IU (20 mcg) daily.
In the United Kingdom, the National Health Service (NHS) recommends 400 IU (10 mcg) daily. It advises everyone to consider supplementing the vitamin during the fall and winter months but notes that those at high risk of deficiency should do so all year round.
Dr. Meltzer notes that although some studies have found that vitamin D improves immune function and decreases inflammation, the evidence has been mixed.
He believes this may be because researchers have been testing doses that are too low to boost the immune system.
â€œBased on these results, we think that earlier studies may have given doses that were too low to have much of an effect on the immune system, even if they were sufficient for bone health,â€ he says.
â€œIt may be that different levels of vitamin D are adequate for different functions,â€ he adds.
A key limitation of the current study is that while it can demonstrate an association between vitamin D levels and SARS-CoV-2 infection risk, it cannot demonstrate that one causes the other.
To address this problem, researchers from the University of Chicago and Rush University in Chicago, IL, are conducting two clinical studies to learn whether taking a daily vitamin D supplement can help prevent COVID-19 or decrease the severity of its symptoms.
Some of the results of the study were surprising. For instance, Black individuals with a vitamin D level of 20â€“30 ng/ml were not at an increased risk of COVID-19 compared with those with a level over 40 ng/ml.
â€œThe significant association of vitamin D levels with COVID-19 risk in Black individuals that was not found in white individuals could reflect their higher COVID-19 risk, to which socioeconomic factors and structural inequities clearly contribute.â€