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Scientists warn against taking high doses of vitamin D for COVID-19

There is good evidence that the excessive intake of vitamin D can be harmful, especially for people with other health issues, such as kidney problems, a team of scientists says.

Vitamin D
Claims of a link between vitamin D supplements and a resistance to COVID-19 — or any acute respiratory tract infection — are not supported by good evidence.
People should not take high doses of vitamin D to prevent or treat COVID-19, warns a team of British, Irish and American scientists.

“There is no strong scientific evidence to show that very high intakes (ie, mega supplements) of vitamin D will be beneficial in preventing or treating COVID-19,” write the 21 scientists in a consensus paper published late last week in the journal BMJ, Nutrition, Prevention and Health.

There is good evidence, however, that the excessive intake of vitamin D can be harmful, especially for people with other health issues, such as kidney problems, they add.

In the United States, the National Academy of Medicine has determined that healthy adults (those without a specific disease related to a vitamin D deficiency) need, on average, 600 international units (IUs) of vitamin D daily — until the age of 71, when they need, on average, 800 IUs.

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Vitamin D is unique among micronutrients, as it’s produced in the skin during exposure to sunlight. So although the vitamin can be obtained through food (such as salmon, egg yolks and fortified milk), just five to 30 minutes of sunlight exposure twice a week is usually sufficient to meet most people’s vitamin D needs, including those living in Minnesota and other northern latitudes.

Even before the coronavirus pandemic, millions of Americans were taking vitamin D supplements unnecessarily and, in some cases, dangerously. A 2017 University of Minnesota study found that one in five American were consuming vitamin D supplements even though experts say that only about 6 percent of Americans are actually deficient in the vitamin.

In recent weeks, unsubstantiated reports that high doses of vitamin D (up to 10,000 IUs daily, according to some accounts) may lower the risk of getting COVID-19 and/or reduce its severity have spread widely across the media, particularly social media. Sales of the supplement have soared as a result, rising by 22 percent in one week alone in March.

Yet, as the consensus paper makes clear, claims of a link between vitamin D supplements and a resistance to COVID-19 — or any acute respiratory tract infection — are not supported by good evidence.

“It is absolutely essential that advice given to the public is evidence-based, accurate and timely,” stress the paper’s authors. “[A]nything less would mislead and has the potential to cause harm.”

Lack of evidence

As the scientists point out, good nutrition and a healthy lifestyle have a positive effect on the body’s immune system, thus helping individuals resist infections. Vitamin D is certainly one of the many nutrients the body needs to stay healthy. It, therefore, should receive our attention — but “not as a ‘magic bullet’ to beat COVID-19, as the scientific evidence base is severely lacking at this time,” write the scientists.

Calls for the widespread use of high-dose vitamin D supplements to contain the spread of COVID-19 are “based on speculations about presumed mechanisms,” they stress. Those presumptions are not yet supported by direct evidence involving humans.

Previous research has suggested a link between vitamin D levels and the risk of developing upper respiratory tract infections, such as the common cold, but many of those studies have been observational. They don’t — and can’t — prove that the two are connected.

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As scientists are frequently heard to say, correlation does not mean causation.

It’s long been observed, for example, that our vitamin D levels tend to dip in the winter. That is also the season when we’re most likely to come down with the flu. But that doesn’t mean low vitamin D levels have anything to do with susceptibility to the flu. Winter is also when we spend more time indoors, which increases our exposure to the respiratory droplets expelled by a cough or sneeze from someone infected with influenza.

In 2017, a meta-analysis of 25 previous clinical trials concluded vitamin D supplementation reduces the risk of respiratory tract infections, particularly among people with low levels of the nutrient in their bodies. But, as the authors of the current consensus paper point out, that meta-analysis had several important limitations. Most notably, two of its studies involved children from the developing countries of Mongolia and Afghanistan. When those two studies are removed from the analysis, the evidence of a benefit from vitamin D supplementation vanishes.

Other research has shown that any kind of treatment tends to be substantially more effective in less developed countries than in developed ones.

A strong immune system

Randomized controlled trials (considered the gold standard of medical research) are currently under way to evaluate the effects of vitamin D supplementation on COVID-19 infections, report the authors of the consensus paper.

“Until there is more robust scientific evidence for vitamin D, we strongly caution against the use of high vitamin D supplementation,” they stress.

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In the meantime, to keep your body — and immune system — healthy, follow this advice from the Harvard Medical School:

  • Don’t smoke.
  • Eat a diet high in fruits and vegetables.
  • Exercise regularly.
  • Maintain a healthy weight.
  • If you drink alcohol, drink only in moderation.
  • Get adequate sleep.
  • Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.
  • Try to minimize stress.

And during the current coronavirus pandemic, practice social distancing, too.

FMI: BMJ, Nutrition, Prevention and Health is an open-access journal, so you can read the consensus paper in full on the publication’s website.