Does Sunlight Kill COVID-19 and Does Vitamin D Prevent It? Experts Explain

Here's what experts know about the effects of UV rays and vitamin D when it comes to COVID-19 protection.

He admitted not being a doctor, but that didn't stop former President Trump from coming up with ideas for how to treat or prevent COVID-19. At the White House COVID-19 task force briefing on April 23, 2020, he suggested that ultraviolet (UV) light could kill the virus, CNN reported. We reached out to infectious disease experts to get their take on sunlight and its effects on COVID-19—turns out, there is something to it.

Trump referenced an "emerging result" from research by the Department of Homeland Security that indicated exposure to sunlight, heat, and humidity seemed to weaken SARS-CoV-2, the virus that causes COVID-19.

Bill Bryan, the then-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 are 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 raised hopes that COVID-19 would become less contagious in the 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."

President Trump's comments caused such an outcry on social media that the World Health Organization (WHO) added to the COVID-19 "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." (For reference, 25 degrees Celsius equals 77 degrees Fahrenheit.)

The Connection Between UV Light and COVID-19

There are three types of UV radiation: UVA, UVB, and UVC. Most rays that come from the sun are UVA rays, with the remaining rays being UVB rays. Additionally, the American Cancer Society said that UVC rays tend to come from artificial sources like mercury bulbs or UV sanitizing bulbs designed to kill germs.

In February 2021, the U.S. Food & Drug Administration (FDA) indicated that "UVB and UVA radiation is expected to be less effective than UVC radiation at inactivating the SARS-CoV-2 coronavirus"—but the FDA also noted that UVC radiation might be helpful in the virus' inactivation.

While it's true that UV light can decrease the viability of viruses on surfaces in general, "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, told 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.

What About the Link Between Sunlight and COVID-19?

Sunlight was in the COVID-19 news cycle for other reasons as well. It's an excellent natural source of vitamin D, which has many purported health benefits, including increased resistance to infectious diseases. When it comes to COVID-19, the research is growing.

Researchers of a May 2021 study published in the Annals of Medicine & Surgery found that "…there exists an interesting link between sunlight exposure, latitude, and vitamin D status with COVID-19 incidence, fatality, and recovery rates that requires further investigation."

A January 2022 study in the Korean Journal of Family Medicine looked at how COVID-19 could be affected by climate. The researchers discovered that there were lower COVID-19 instances when higher humidity, air temperature, and exposure to sunlight were involved.

Thus, it sounds as if there is a potential for sunlight to be helpful against COVID-19. It may help to lower the risk of a more severe respiratory infection, Cynthia Sass, RD, Health contributing nutrition editor, told Health.

"The goal is to achieve adequate blood levels of vitamin D to best support immune function," explained Sass. Sass said 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," said Sass.

Vitamin C and COVID-19

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," said Sass.

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, warned Sass.

If you take the right dose of vitamin D, your health could benefit in numerous ways. But as Sass said, no supplement can stop you from getting COVID-19.

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 CDC, WHO, and their local public health department as resources.

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  2. World Health Organization (WHO). COVID-19 mythbusters.

  3. Centers for Disease Control and Prevention (CDC). Ultraviolet radiation.

  4. American Cancer Society (ACS). Ultraviolet (UV) radiation: What is UV radiation?.

  5. U.S. Food & Drug Administration (FDA). UV lights and lamps: Ultraviolet-C radiation, disinfection, and coronavirus.

  6. Sharun K, Tiwari R, Dhama K. COVID-19 and sunlight: Impact on SARS-CoV-2 transmissibility, morbidity, and mortalityAnn Med Surg (Lond). 2021;66:102419.

  7. Kato M, Sakihama T, Kinjo Y, Itokazu D, Tokuda Y. Effect of climate on covid-19 incidence: a cross-sectional study in JapanKorean J Fam Med. 2022;43(1):37-41.

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