- Vitamin D deficiency has previously been linked to a higher risk of contracting COVID-19 and developing more serious disease, especially among Black and Hispanic people.
- According to a new observational report, also “sufficient” vitamin D levels, as established by current guidelines, are linked to a higher risk of COVID-19 in Black people.
- Vitamin D status is currently assessed based on preserving bone health rather than immune function.
Vitamin D has a variety of functions in the body, including calcium regulation, bone and tooth protection, and immune system support.
In addition to having vitamin D from food, the body can develop it in the skin by exposing it to sunlight.
However, maintaining adequate amounts of the vitamin can be difficult for people with dark skin and those who do not get enough sunlight, particularly during the winter months.
According to one study, almost half of all Americans are vitamin D deficient. Among Black people, the figure rose to 82 percent, and among Hispanics, it was 70 percent.
SARS-CoV-2, the virus that causes COVID-19, is more likely to test positive in people with low vitamin D levels, according to growing evidence. They may also be at a higher risk of contracting a serious illness.
This connection could explain why Black, Hispanic, and other non-white populations have been disproportionately affected by the pandemic.
Vitamin D supplements have been shown in clinical trials to assist in the prevention of other viral respiratory infections.
According to the existing recommendations, taking a vitamin D supplement can also minimize viral infections in people who are not vitamin D deficient. These dosages are focused on what’s needed to keep your bones in good condition.
Dr. David Meltzer, Ph.D., and his colleagues at the University of Chicago, IL, wondered whether vitamin D and COVID-19 could be treated similarly.
Vitamin D blood tests
The researchers looked at the medical history of 4,638 people who had a vitamin D blood test at the University of Chicago Medical Center 12 months before a PCR test for SARS-CoV-2 (UChicago Medicine).
The researchers calculated the participants’ vitamin D levels 14 days before the PCR test using the time before the vitamin D test and subsequent treatments.
They also took into account factors that have been related to an increased risk of COVID-19, such as age, sex, race, and medical conditions.
In total, 211 black people and 102 white people tested positive for SARS-CoV-2.
The researchers discovered that those with a serum vitamin D level of 30–39.9 nanograms per milliliter (ng/ml) — a “sufficient” level — had 2.64 times the chance of testing positive compared to those with a level of at least 40 ng/ml.
In other words, having levels beyond the range considered adequate by experts seemed to have a major protective impact.
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.
“These new findings indicate that having vitamin D levels above those deemed acceptable is associated with a lower risk of testing positive for [SARS-CoV-2], at least in Black people,” says Dr. Meltzer, the study’s lead author and chief of hospital medicine at UChicago Medicine.
“This 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,” he adds.
In white people, there were no statistically significant ties between vitamin D levels and the risk of testing positive for SARS-CoV-2.
This, according to the researchers, is due to the low number of positive SARS-CoV-2 tests among white people in their study.
Likewise, the number of participants from other ethnic groups, such as Hispanics, was insufficient to produce statistically meaningful results.
The research was published in JAMA Network Open.
Case for high dose supplements
The researchers write in their paper, “These findings increase the urgency to consider whether increased sun exposure or vitamin D supplementation could reduce COVID-19 risk.”
Vitamin D levels greater than 40 ng/ml are present in less than 5–10% of adults in the United States, according to the researchers. It will take more than the currently prescribed daily dose of a vitamin to reach these amounts without raising sun exposure.
“Lifeguards, surfers; those are the kinds of folks who tend to have more than sufficient vitamin D levels,” says Dr. Meltzer. “In the winter, most people in Chicago will have amounts that are far below that.”
For adults aged 19–70 years, the National Institutes of Health (NIH) recommends 600 international units (IU), or 15 micrograms (mcg), per day. The recommended daily volume for adults 71 years and older is 800 IU (20 mcg).
The National Health Service (NHS) in the United Kingdom recommends 400 IU (10 mcg) per day. It recommends that everyone take vitamin D supplements during the fall and winter months, but that those at high risk of deficiency should do so all year.
While some studies have shown that vitamin D enhances immune function and reduces inflammation, the evidence is mixed, according to Dr. Meltzer.
He assumes it’s because researchers have been dealing with immune-boosting doses that are too low.
“Based 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,” he says.
He adds, “It’s possible that different levels of vitamin D are sufficient for different functions.”
The current study has a major flaw: while it can show a correlation between vitamin D levels and the risk of SARS-CoV-2 infection, it cannot show that one triggers the other.
To fix this concern, researchers at 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.
Socioeconomic inequality
Some of the study’s findings were unexpected. In contrast to those with a level over 40 ng/ml, Black people with a vitamin D level of 20–30 ng/ml did not have an elevated risk of COVID-19.
Furthermore, those with a COVID-19 risk of less than 20 ng/ml seemed to have a lower risk than those with a risk of 30–40 ng/ml. The authors speculate that differences in vitamin D treatment could explain the discrepancies, but they indicate that more research is needed in this area.
The writers of the new study also point out that social and economic inequities contribute to Black people’s increased vulnerability to COVID-19.
They write:
The 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.”
