Sunlight Energizes Infection-Fighting Cells

The health benefits of vitamin D — the “sunshine vitamin” that’s made by the body when skin is exposed to sunlight — are well-known and range from building healthy bones to protecting the brain and reducing the risk of cancer and diabetes.

But the sun itself may provide a powerful stimulant to the immune system via a mechanism that is separate from the production of vitamin D. Researchers at Georgetown University Medical Center found sunlight energizes T cells, a type of white blood cell that plays a major role in immunity.

“We all know sunlight provides vitamin D, which is suggested to have an impact on immunity, among other things. But what we found is a completely separate role of sunlight on immunity,” said the study’s senior investigator, Gerard Ahern, Ph.D.

“Some of the roles attributed to vitamin D on immunity may be due to this new mechanism,” he said.

They specifically found that low levels of blue light, found in sun rays, make T cells move faster. It’s the first time scientists have found that human cells respond to sunlight by speeding their pace.

“T cells, whether they are helper or killer, need to move to do their work, which is to get to the site of an infection and orchestrate a response,” Ahern says. “This study shows that sunlight directly activates key immune cells by increasing their movement.”

“We found that sunlight makes hydrogen peroxide in T cells, which makes the cells move. And we know that an immune response also uses hydrogen peroxide to make T cells move to the damage,” Ahern says. “This all fits together.”

Ahern says that if activating T cells with blue light has only beneficial effects, it might make sense to offer patients blue light therapy to boost their immunity.