There might be something to it. Here's what experts know about the effects of UV rays and vitamin D when it comes to coronavirus protection.

By Claire Gillespie
April 24, 2020
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He admits he’s not a doctor, but that doesn’t stop President Trump from coming up with ideas for how to treat or prevent COVID-19. At the White House coronavirus task force briefing on April 23, he suggested that ultraviolet (UV) light can kill the virus, CNN reported.   

He referenced an “emerging result” from research by the Department of Homeland Security that indicates exposure to sunlight, heat, and humidity seems to weaken the coronavirus. 

Bill Bryan, the acting homeland security undersecretary for science and technology, said at the briefing: “Our most striking observation to date is the powerful effect that solar light appears to have on killing the virus—both surfaces and in the air. We’ve seen a similar effect with both temperature and humidity as well, where increasing the temperature and humidity or both is generally less favorable to the virus.”

Bryan added that the virus dies quickest when three environmental factors combine: a high temperature, high humidity, and direct sunlight. This has raised hopes that the coronavirus could become less contagious in summer months, and prompted President Trump to speculate that “hitting the body with a tremendous” ultraviolet or “just very powerful light” could get rid of the infection. He even suggested somehow bringing “the light inside the body [...] either through the skin or in some other way.”

Right now, there’s not much to go on. The research hasn't been published, so it's not known how much UV light would be required to have an effect on the coronavirus. But we reached out to infectious disease experts to get their take on it—and it turns out there is something to it.

It’s true that UV light can decrease the viability of viruses (including the new coronavirus) on surfaces, but "that doesn’t mean people with COVID-19 who expose themselves to UV light—or sunlight, which contains UV radiation—will get rid of the infection,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health

There’s also the fact that UV light comes with some potentially serious health risks. UV rays can penetrate and damage skin cells, and overexposure to UV can lead to skin cancer. 

President Trump’s comments caused such an outcry on social media that the World Health Organization (WHO) added to the coronavirus “myth busters” page on its website: “Exposing yourself to the sun or to temperatures higher than 25C degrees DOES NOT prevent the coronavirus disease. You can catch COVID-19, no matter how sunny or hot the weather is. Countries with hot weather have reported cases of COVID-19.” (25 degrees Celsius equals 77 degrees Fahrenheit.)

Sunlight has been in the coronavirus news cycle recently for another reason. It’s an excellent natural source of vitamin D, which has many purported health benefits, including an increased resistance to infectious diseases. But when it comes to COVID-19, the research is limited. Clinical trials have started in Spain and France to see if vitamin D improves outcomes for COVID-19 patients, but so far there’s no evidence that vitamin D reduces the risk of contracting the coronavirus. However, it may help to lower the risk of a more severe respiratory infection, Cynthia Sass, MPH, RD, Health contributing nutrition editor, tells Health

“The goal is to achieve adequate blood levels of vitamin D to best support immune function,” explains Sass. She says the best approach is to have a blood test to find out if your blood vitamin D level is within the adequate range. “This determines if a supplement is needed in order to achieve adequate blood vitamin D status, and if so, the proper dosage of supplemental vitamin D,” she says.

It’s important to be careful with doses of vitamin D supplements—more isn’t better. “High doses of vitamin D can trigger unwanted side effects, which may include increased blood calcium levels, negatively impacting the heart, blood vessels, and kidneys. Other side effects may include irregular heartbeat and digestive upset,” Sass says. 

If you can't get your blood vitamin D status tested, Sass recommends doing one of three things to raise your blood levels without risking too much vitamin D: incorporate into your diet more vitamin D-rich foods, such as egg yolks, wild salmon, tuna, fortified foods, and mushrooms that have been exposed to UV light; take a daily supplement that provides 800-2000 IU of vitamin D; or consume a combination of the two. 

The tolerable upper Intake Level (UL) for vitamin D (the maximum daily intake from both food and supplements combined that is unlikely to cause adverse health effects) is 4000 IU, so don't exceed this level without medical supervision, Sass warns. 

If you take the right dose of vitamin D, your health could benefit in numerous ways. But as Sass says, no supplement can stop you from getting the coronavirus. 

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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