Vitamin D won’t protect you from Covid or respiratory infections, studies show

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Vitamin D supplementation at either dose “did not reduce the risk of all-cause acute respiratory infections (ARIs), nor the risk or severity of COVID-19 specifically. “said study author Dr. Adrian Martineau, Professor of Respiratory Infection and Immunity at the Institute of Population Health Sciences at Queen Mary University of London via email.

A second randomized double-blind clinical trial, also done during the pandemic, gave more than 34,000 Norwegians cod liver oil or a placebo to test the impact of vitamin D on Covid and the prevention of respiratory disease. Cod liver oil naturally contains low doses of vitamin D, as well as vitamin A and omega-3 fatty acids.

The British Medical Journal published the two studies on Wednesday.

“The main takeaway is that for people in general, vitamin D supplementation did not prevent COVID-19, severe COVID-19, or symptomatic acute respiratory infections,” the author said. the study, Dr. Arne Søraas, a researcher in the department of microbiology at Oslo University Hospital in Norway, in an email.

Vitamin D can be toxic at high levels because any excess is stored in the body.

Søraas added that the design of the UK study “complements ours in several ways, with a higher dose of vitamin D given to participants only after measuring their vitamin D status. in vitamin D.”

The findings of the two studies contradict a study carried out in 2020 in Mexico City, where healthcare professionals were given either 4,000 IU of vitamin D daily or a placebo. Researchers found protective effects of the vitamin in just one month. Two other ongoing clinical trials in the United States and Canada will add more data, Martineau said.

The studies were done before the vaccines were widely available, the two authors noted. “We can be absolutely sure that vaccination is much more effective than vitamin D, which probably does not prevent 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, 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.

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Research has shown that vitamin D deficiency weakens the immune systemand some Studies have shown that vitamin D supplements can reduce the risk of respiratory viral infections and calm overreaction of the immune system.

Early in the pandemic, frontline doctors began noticing that 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 extra doses of vitamin D – even if it wasn’t necessary – would prevent the coronavirus from taking hold.

However, “unlike vitamin C, vitamin D is a fat-soluble vitamin that can ‘build up’ in the system and cause toxicity if taken in very high doses over long periods of time,” Martineau explained.

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Research has suggested that long-term use of higher levels of vitamin D is associated with increased all-cause mortality, increased risk of cancer, cardiovascular events, and more falls and fractures in old people.

The recommended daily dose of vitamin D for people in the United States between the ages of 1 and 70 is 600 international units (IU) per day, increasing to 800 IU per day for those over 70. In the UK, the recommended daily amount is 400 IU per day. Levels in other parts of the world are country specific to reflect environmental and dietary differences, but generally between 400 and 800 IU per day.

Studying People With Low Vitamin D Levels

The UK study was part of COVIDENCE UNITED KINGDOM, a nationwide study designed to investigate risk factors for developing Covid-19. The researchers recruited 6,200 adults, aged 16 or older, who were not taking vitamin D supplements, and conducted the study between December 2020 and June 2021.

A random sample of participants underwent a vitamin D blood test and 3,100 people had low vitamin D levels. The other 3,100 people were designated as controls.

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Study participants with low levels of vitamin D were then randomized into two groups of 1,550 people who were assigned to take 3,200 IU or 800 IU of a vitamin D supplement each day for six months. However, the study was not blinded or placebo-controlled: each person knew they were taking a supplement provided by two pharmaceutical companies that supported the study.

During the six months of the trial, neither the high dose nor the low dose of vitamin D had any effect in preventing respiratory tract infections or confirmed cases of Covid-19 compared to the control group, according to the study.

The results contradict two previous meta-analyses of randomized clinical trials conducted by Martineau and colleagues who found a significant, albeit small, impact on protection against respiratory disease.

Use a low dose

The Norwegian study, conducted between November 2020 and June 2021, divided 34,601 people aged 18 to 75 into two groups. Each group took either 1 teaspoon (5 milliliters) of cod liver oil or 1 teaspoon of corn oil, which served as a placebo, every day for six months during the winter.

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Each teaspoon of cod liver oil contained about 400 IU (10 micrograms) of vitamin D, Søraas said. Cod liver oil is a staple in Norway, 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 using vitamin D supplements before enrollment.

Unlike the UK study, where many people were vitamin D deficient, the tests in Norway showed that 90% of people in the cod liver oil group and 72% of those in the placebo had adequate levels. at the start of the study: “But we did not find that this measure influenced the risk of contracting COVID-19 or other acute respiratory infections,” Søraas said.

However, like the UK study, the Norwegian study found that vitamin D in cod liver oil had no preventative impact on respiratory infections or confirmed cases of Covid-19.

“The overall message is consistent – two differently designed studies looking at related interventions in slightly different populations – but the same result – no observed effect,” said Martineau, author of the UK study.

“As a doctor, I see a lot of speculation that very high doses of vitamin D could have benefits for a range of different illnesses, but I encourage everyone to follow science-based government recommendations. for all the nutrients,” Søraas said.

“Our results support existing recommendations that do not include massive doses.”

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