FRIDAY, April 9, 2021 (HealthDay News) -- COVID-19 might have a tough new foe: The sun.
New research shows that sunnier regions of the United States have lower COVID-19 death rates than cloudier areas, suggesting that the sun's UV rays might somehow provide some protection against the disease.
The effect is not due to better uptake of the healthy "sunshine vitamin," vitamin D, noted the Scottish research team led by Richard Weller, of the University of Edinburgh.
"The effect appears independent of a vitamin D pathway," the researchers reported, and they also stressed that the study wasn't designed to prove a cause-and-effect relationship.
However, if sunshine does help prevent severe COVID-19, "optimizing sun exposure may be a possible public health intervention," the study authors concluded.
The new report was published April 8 in the British Journal of Dermatology.
For the study, Weller's group analyzed all recorded COVID-19 deaths in the continental United States from January to April 2020, and then compared that with data on levels of the sun's ultraviolet (UV) rays in nearly 2,500 U.S. counties during the same period.
People in regions with the highest level of exposure to UVA rays (which make up 95% of the sun's UV light) were less likely to die of COVID-19 than those in regions with the lowest levels of UVA exposure, the findings showed.
The researchers conducted similar analyses in England and Italy and came up with the same results. Averaging the results of the three studies, the Scottish team said that for every increase of 100 kilojoules per square meter of sunlight (a standard measure) in a given area, the odds of dying from COVID-19 fell by about one-third.
The investigators tried to account for certain factors associated with risk of coronavirus infection and death, such as age, ethnicity, wealth, population density, air pollution, temperature and local infection rates.
The association between greater sun exposure and a lower risk of death from COVID-19 couldn't be explained by higher levels of vitamin D because only regions with levels of UVB that were too low to produce significant vitamin D in the body were included in the study, the authors said.
So how might extra sunlight curb COVID-19?
According to Weller's group, one possible explanation is that sun exposure causes the skin to release a chemical called nitric oxide. Some laboratory studies have found that nitric oxide may reduce the ability of the new coronavirus to replicate and spread. The study authors are planning to follow-up with more research regarding this theory.
Previous research by the same team found that increased sunlight exposure is associated with better heart health, lower blood pressure and fewer heart attacks. Heart disease is a known risk factor in dying from COVID-19, so that past research could also help explain the new findings, they suggested.
Two COVID-19 experts in the United States agreed that the findings were intriguing, but merited more study.
"The research does not establish a cause and effect, and represents an association at best," stressed Dr. Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York City. He wasn't surprised that vitamin D wasn't credited with any health benefit.
"While there is evidence that vitamin D may have beneficial effects on immune function, a specific antiviral effect remains unproven at this time," Glatter said. "In fact, a randomized controlled study of people with moderate to severe COVID-19 who received high-dose vitamin D demonstrated no benefit."
Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, in Baltimore, is an expert on viruses. He said the research raises interesting questions, but the nitric oxide hypothesis needs more study.
"Putting that link together to show the mechanism of how this is happening, I think that's where you'd want to see this line of research go, in order to show that there's also a vitamin D-independent benefit of sunlight," Adalja said.
The U.S. Centers for Disease Control and Prevention has more on COVID-19 prevention.
SOURCES: Amesh Adalja, MD, senior scholar, Center for Health Security, Johns Hopkins Bloomberg School of Public Health, Baltimore; Robert Glatter, MD, emergency medicine physician, Lenox Hill Hospital, New York City; British Journal of Dermatology, April 8, 2021;University of Edinburgh, news release, April 8, 2021