Vitamin D supplementation at either dose “did not reduce the risk of all-cause acute respiratory infection (ARI), or specifically the risk or severity of COVID-19,” study author Dr. Adrian Martineau, professor of respiratory infections and immunology at the Institute of Population Health Sciences at Queen Mary University of London, emailed.
The British Medical Journal published the two studies on Wednesday.
“The main takeaway is that in the average person, vitamin D supplementation does not protect against COVID-19, severe COVID-19, or symptomatic acute respiratory infection,” said study author Dr. Arne Søraas, a researcher in the Department of Microbiology. Oslo University Hospital, Norway, in an email.
Søraas added that the UK study design “complements ours in several ways, giving higher doses of vitamin D only after the participants’ vitamin D status was measured. However, their results support our findings, which Also key: Neither study found any preventive effect after vitamin D supplementation.”
Both authors noted that these studies were done before a vaccine was widely available. “We can be absolutely sure that vaccination is more effective than vitamin D, which may not protect against COVID-19 at all,” Søraas said.
The popularity of vitamin D
The main function of vitamin D is to help the body absorb calcium and phosphate to keep muscles and teeth healthy and bones strong and less prone to breakage. However, vitamin D also helps the immune system fight off invading bacteria and viruses.
Early in the pandemic, doctors on the front lines began noticing that people with lower vitamin D levels appeared to be at a higher risk of dying from Covid-19. Suddenly, the internet was flooded with speculation that taking supplemental doses of vitamin D — even if it wasn’t needed — could protect against coronavirus.
However, “unlike vitamin C, vitamin D is a fat-soluble vitamin, and if taken in very high doses over a long period of time, it can ‘build up’ in the system and cause toxicity,” explains Martineau.
Studies have shown that long-term use of higher levels of vitamin D is associated with increased all-cause mortality, increased cancer risk, cardiovascular events, and increased falls and fractures in older adults.
Studying people with low vitamin D levels
Vitamin D blood tests were done on a random sample of participants and 3,100 people were found to have low levels of vitamin D. The other 3,100 were assigned as controllers.
Study participants with low vitamin D levels were then randomized into two groups of 1,550, who were assigned to take either 3,200 IU or 800 IU of vitamin D supplements daily for six months. However, the study was not blinded or placebo-controlled: everyone knew they were taking supplements provided by the two pharmaceutical companies that backed the study.
The study showed that neither high or low doses of vitamin D had any effect on preventing respiratory infections or confirmed cases of Covid-19 compared to the control group during the six-month period of the trial.
use low doses
The Norwegian study, conducted between November 2020 and June 2021, divided 34,601 people between the ages of 18 and 75 into two groups. Each group received 1 teaspoon (5 ml) of cod liver oil or 1 teaspoon corn oil daily as a placebo for six months throughout the winter.
Cod liver oil contains about 400 IU (10 micrograms) of vitamin D per teaspoon, Søraas says. Cod liver oil is a staple in Norway and has been used for centuries to add vitamin D and omega-3 fatty acids to the Norwegian diet. However, 75.5% of people in the study were not taking vitamin D supplements before enrollment.
Unlike the UK study where many people were vitamin D deficient, tests in Norway showed that 90% of people in the cod liver oil group and 72% in the placebo group had adequate levels of vitamin D At the start of the study: “But we didn’t find that this measure affected the chances of contracting COVID-19 or other acute respiratory infections,” Søraas said.
However, like the UK study, the Norwegian study found no protective effect of vitamin D in cod liver oil against respiratory infections or confirmed cases of Covid-19.
“The overall message was consistent — two studies with different designs looked at the relevant intervention in slightly different populations — but the bottom line was the same — and no effect was seen,” said UK study author Martineau.
“As a doctor, I see a lot of speculation that very high doses of vitamin D may have beneficial effects on a range of different diseases, but I encourage everyone to follow science-based government recommendations for all nutrients,” says Søraas .
“Our results support existing recommendations for excluding high doses.”