High vitamin D levels may protect against COVID-19: Study

Black Americans are infected with COVID-19 at nearly three times the rate of White Americans, according to a report​ from the National Urban League. The report also shows Black Americans are twice as likely to die from the virus. 

David Meltzer, MD, PhD, chief of hospital medicine at UChicago Medicine and lead author of the study, said a number of components are working in concert to create a perfect storm. 

“I believe that many factors contribute to this, including socioeconomic factors such as whether one has a job that allows one to work from home or enough economic resources to protect oneself, and access to health care. I think vitamin D may also contribute to differences in COVID-19 risk and outcomes by race and deserves serious attention as a contributor. We need to work on all these fronts.”​

A report in early 2020 that found people with vitamin D deficiency who had randomly been assigned to receive vitamin D supplementation had much lower rates of viral respiratory infections compared to those who did not receive supplementation. After Meltzer read about the study, he was motivated to do his own research, and began examining  data being collected at UChicago Medicine.

"There's a lot of literature on vitamin D. Most of it has been focused on bone health, which is where the current standards for sufficient vitamin D levels come from,"​ Meltzer explained. "But there's also some evidence that vitamin D might improve immune function and decrease inflammation. So far, the data has been relatively inconclusive. 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. It may be that different levels of vitamin D are adequate for different functions."​

Currently, the adult recommended dietary allowance for vitamin D is 600 to 800 international units (IUs) per day. According to Meltzer, the National Academy of Medicine has said that taking up to 4,000 IUs per day is safe for the vast majority of people, and risk of hypercalcemia increases at levels over 10,000 IUs per day. 

The study

The research, published in JAMA Open Network​, retrospectively examined the relationship between vitamin D levels and likelihood of testing positive for COVID-19. 

The study looked at data from over 3,000 patients at UChicago Medicine who had had their vitamin D levels tested within 14 days before a COVID-19 test.

While levels of 30 ng/ml or more are usually considered "sufficient," the authors found that Black individuals who had levels of 30 to 40 ng/ml had a 2.64 times higher risk of testing positive for COVID-19 than people with levels of 40 ng/ml or greater. Statistically significant associations of vitamin D levels with COVID-19 risk were not found in White people. 

“We do not know why these differences exist but several reasons come to mind,” ​explained Meltzer. “One is that White people in our sample may have been less likely to be in jobs or living situations that exposed them to the virus, so their risk is lower overall, and that would make it harder to see significant associations between vitamin D levels and the risk of COVID-19 even if the underlying biology was the same.  Another is that White people tend to have higher vitamin D levels, so there are fewer White people with the lower vitamin D levels where vitamin D may make a difference in the risk of developing COVID-19. A third is that White people are more likely to have vitamin D binding proteins that allow vitamin D to be used by the immune system even when vitamin D levels are low. A fourth is that White people may less rapidly break down vitamin D than Black people so lower levels in the blood are more effective in White people than they would be in Black people.”​

This research is an expansion of an earlier study showing that a vitamin D deficiency (less than 20 ng/ml) may raise the risk of testing positive for COVID-19. In the current study, those results were further supported, finding that individuals with a vitamin D deficiency had a 7.2% chance of testing positive for the virus. A separate study recently found that over 80% of patients diagnosed with COVID-19 were vitamin D deficient.

"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 Meltzer. "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."​

What is it about vitamin D?

The observational study does show an association between vitamin D levels and likelihood of a COVID-19 diagnosis, however, the mechanisms are unclear.

Meltzer told NutraIngredients-USA​ that vitamin D improves several aspects of the immune system that are important in the fight against COVID-19. 

“First, it improves innate immunity, the ability to fight off an infection one has never been exposed to before. Second, vitamin D helps adaptive immunity, the ability to fight off an infection one has been exposed to before, which may be beneficial in the later stages of even a first COVID-19 infection. Finally, vitamin D is an immunomodulator, which helps prevent the body from having too strong an inflammatory reaction to a COVID-19 infection that may result in symptoms such as shortness of breath,”​ explained Meltzer. 

Location may play a role 

Meltzer noted that most individuals, especially people with darker skin, have lower levels of vitamin D, with roughly half of the world's population with levels below 30ng/ml.

"Lifeguards, surfers, those are the kinds of folks who tend to have more than sufficient vitamin D levels,"​ he said. "Most folks living in Chicago in the winter are going to have levels that are well below that."​

According to Meltzer, there are now several studies suggesting that the risk or severity of COVID-19 is  related to the latitude one lives in, with people living in more northern areas generally at higher risk of developing COVID-19 or having more severe outcomes.

More research 

Prompted by the evidence that people with vitamin D deficiency are more likely to test positive for COVID-19 and experience significant symptoms, a team at the University of Chicago and Rush University is conducting two studies to learn whether taking a daily vitamin D supplement can help prevent COVID-19 or decrease the severity of its symptoms.

The UChicago Medicine research team is now recruiting participants for two separate clinical trials testing the efficacy of vitamin D supplements for preventing COVID-19.

Individuals who would like to learn more about the study and determine their eligibility can visit chess.uchicago.edu/vitamind​. 

Source: JAMA Network Open​

2021;4(3):e214117. doi:10.1001/jamanetworkopen.2021.4117​

"Association of Vitamin D Levels, Race/Ethnicity, and Clinical Characteristics with COVID-19 Test Results”​

Authors: D. Meltzer et al.