March 19 (UPI) -- Black people in the United States with low levels of vitamin D in their blood are nearly three times as likely to contract COVID-19 than those with healthy amounts of the nutrient, a study published Friday by JAMA Network Open found.
Conversely, Black people with healthy levels of vitamin D had a 25% lower risk for infection, the data showed.
Nearly 10% of Black study participants with low levels of the nutrient tested positive for COVID-19, compared to less than 4% of those with high amounts in their blood.
"At least for [Blacks in the United States], having vitamin D levels higher than those that have traditionally been considered adequate may reduce the risk of developing COVID-19," study co-author Dr. David Meltzer told UPI in an email.
"We found that having a vitamin D level as high as 30 to 40 nanograms per milliliter [in the blood], which is usually considered adequate, is associated with a two- to three-fold increased risk of testing positive for COVID-19, compared to [higher] levels," said Meltzer, director of the Center for Health and the Social Sciences at the University of Chicago.
Vitamin D plays a significant role in immune system function, according to Meltzer and his colleagues.
People with less than 20 nanograms per milliliter of the nutrient in the blood are considered "deficient," and may have poorer immune response to viruses and other pathogens, the researchers said.
As many as 60% of adults in the United States are vitamin D deficient, Meltzer estimated.
For this study, he and his colleagues analyzed data on more than 4,600 adults who had been assessed for vitamin D levels within one year prior to undergoing testing for COVID-19.
Among the study participants, 2,288, or 49%, were Black and 1,999, or 43%, were White.
In addition, 1,251 participants, or 27%, were vitamin D deficient at the start of the study, including 36% of Black people and 16% of White people enrolled, according to the researchers.
Of the study participants, 333, or 7%, tested positive for COVID-19, including 102, or 5%, of the White people and 211, or 9%, of the Black people enrolled, the researchers said.
Compared to those with health amounts of the nutrient -- 40 nanograms per milliliter or more -- Black people who were vitamin D deficient were roughly 2.6-times as likely to test positive for the virus, the data showed.
Most Black Americans have low levels of vitamin D, "especially if they do not take a vitamin D supplement [and], given the low risks of supplementation at low to moderate doses, our findings suggest that taking a supplement ... may be reasonable," Meltzer said.
"Randomized trials are needed to know with certainty whether vitamin D supplementation can reduce the risk of developing COVID-19, [and] we are currently recruiting for several clinical trials" for that purpose, he said.