Vitamin D supplements fail to prevent Covid in studies
Vitamin D supplements don’t help to prevent Covid-19 infection or other acute respiratory tract infections, according to two new studies, countering previous studies showing a protective effect.
One study, done in the United Kingdom during the height of the pandemic, gave 3,100 people with insufficient levels of vitamin D a low or a high dose of the vitamin to see if the supplement would prevent a coronavirus or respiratory infection.
Vitamin D supplementation at either dose "did not result in reduced risk of all-cause acute respiratory infections (ARI), or in risk or severity of COVID-19 specifically," said study author Dr. Adrian Martineau, a professor of respiratory infection and immunity at the Institute of Population Health Sciences at Queen Mary University of London via email.
A second double-blinded, randomized clinical trial, also done during the pandemic, gave over 34,000 Norwegians cod liver oil or a placebo to test the impact of vitamin D on Covid and respiratory disease prevention. Cod liver oil naturally contains low doses of vitamin D, along with vitamin A and omega-3 fatty acids.
The British Medical Journal released both studies Wednesday.
"The major takeaway is that for people in general, a vitamin D supplement did not prevent COVID-19, serious COVID-19 or symptomatic acute respiratory tract infections," said study author Dr. Arne Søraas, a researcher in the department of microbiology at Oslo University Hospital in Norway, in an email.
The findings of both studies counter a study done in 2020 in Mexico City, where health professionals were given either 4,000 IU of vitamin D a day or a placebo. Researchers found protective effects from the vitamin in just one month. Two more clinical trials that are underway in the United States and Canada will add more data, Martineau said.
The studies were done before vaccinations were widely available, both authors noted. "We can be completely sure that vaccination is way more effective than vitamin D which probably does not prevent COVID-19 at all," Søraas said.
The primary function of vitamin D is to help the body absorb calcium and phosphate, thus keeping muscles and teeth healthy and bones strong and less likely to break. However, vitamin D is also known to help the immune system fight off invading bacteria and viruses.
Research has shown that vitamin D deficiency impairs the immune system, and some studies have found vitamin D supplements may reduce the risk of respiratory virus infections and calm immune system overreaction.
During the early days of the pandemic, physicians on the front lines began noticing people with lower levels of vitamin D appeared to have a higher risk of dying from Covid-19. Suddenly, the internet was flooded with speculation that taking supplemental doses of vitamin D -- even if not needed -- would prevent the coronavirus from taking hold.