Since the pandemic began, sales of vitamin D and other supplements promoted for immune health have soared. But preliminary studies of vitamin D and Covid-19 have yielded mixed results.
At the University of Chicago Medicine, which serves a largely black and Hispanic population on the South Side of Chicago, researchers reviewed the medical records of more than 4,300 patients, many of them health care workers, who were tested for Covid-19 in March and early April.
After controlling for factors that can influence vitamin D levels, like age, race and chronic medical conditions, they found that people who were vitamin D deficient before the pandemic began were 77 percent more likely to test positive for Covid-19 compared to people who had normal levels.
Dr. David Meltzer, a professor of medicine at the University of Chicago and the lead author of the study, which has not yet been peer reviewed, cautioned that the findings were correlational and did not prove causation. He said he and his colleagues were recruiting local paramedics, police officers and other emergency workers for a randomized trial that will test whether taking low to moderate doses of vitamin D daily has an impact on their risk of developing Covid-19 or the severity of their symptoms. Dr. Meltzer suspects that people taking vitamin D who contract the virus will have fewer symptoms of Covid-19 “because the immune system will be less likely to have an exaggerated inflammatory response.”
“I think you can learn a lot from observational studies,” said Dr. Meltzer, who is chief of the Section of Hospital Medicine at the University of Chicago Medicine. “But in the end we desperately need randomized trials to determine as rapidly as we can if there’s a real effect here.”
In Britain people from minority ethnic groups, such as those with African or South Asian ancestry, make up a third of all confirmed cases of Covid-19 in critical care, even though they account for just 14 percent of the population. They also experience higher levels of poverty, chronic diseases and vitamin D deficiencies. At least one medical group, the British Association of Physicians of Indian Origin, has urged all British health care workers from minority backgrounds to consider taking vitamin D supplements as a precaution.
But two recent studies using data from the U.K. Biobank, a long running project that has tracked the health of a half million people aged 40 to 69, cast doubt on the links between vitamin D and Covid-19. One group of researchers found that participants who recently tested positive for coronavirus were more likely to have had very low or deficient levels of vitamin D compared to other participants. But the association disappeared after the results were adjusted for factors like age, race, obesity and socioeconomic status.