Markham Heid writes:

Last month, during a now-infamous press conference, Donald Trump speculated about the ways in which sunlight and chemical disinfectants could help protect people from the threat of Covid-19. Trump seemed to suggest that injecting disinfectants could have some utility — a comment that drew immediate scrutiny and scorn.

Much less attention was paid to the president’s statement that sunlight might safeguard people from the virus. “Supposing we hit the body with a tremendous — whether it’s ultraviolet or just very powerful light,” Trump said. “Supposing you brought the light inside the body, which you can do either through the skin or in some other way.”

When it comes to potential Covid-19 treatments, the president’s speculations have been numerous and frequently misguided. But the idea that sunlight could counteract Covid-19, both inside and outside the body, is not all that far-fetched.

Richard Weller, MD, is a dermatologist and sunlight researcher at the University of Edinburgh in the U.K. Weller says he’s looked at Covid-19 data in the United States, and that there seems to be a correlation between states that get a lot of sun and lower rates of death. “I think there are probably several pathways by which sunlight and sun exposure may exert beneficial effects,” he says.

For thousands of years, humans have recognized that the seasons play a role in the emergence and transmission of certain illnesses, including viruses. “Annual epidemics of the common cold and influenza disease hit the human population like clockwork in the winter,” write the authors of a 2020 review paper from a team at the Yale University School of Medicine. They also point out that two deadly coronaviruses — first SARS, and now Covid-19 — both emerged during the winter months. “[This indicates] that the winter environment promotes the spread of a variety of respiratory virus infections,” they write.

While the seasonality of many common respiratory illnesses is well-established, it may surprise some to learn that experts haven’t nailed down the exact causes of this phenomenon. For the most part, they tend to agree that a mix of environmental factors — such as temperature and humidity — play a role in pathogen transmission. So does human behavior; people are more likely to crowd together indoors during the winter months, and stagnant indoor air can increase the likelihood of spreading germs. But that Yale review also lists sunlight as a possible explanation for the seasonality of certain pathogens. [Continue reading…]