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Sunlight offers surprise benefit
January 3, 2017, 11:38 am

Sunlight allows our body to make vitamin D, which is credited with healthier living, but now a new research finding reveals another powerful benefit of getting some sun.

Researchers at Georgetown University Medical Center in the United States have found that sunlight, through a mechanism separate from vitamin D production, energizes T cells that play a central role in human immunity. Their findings, suggest how the skin, the body's largest organ, stays alert to the many microbes that can nest there.

"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 one senior investigator involved in the study. "Some of the roles attributed to vitamin D on immunity may be due to this new mechanism."

The researchers specifically found that low levels of blue light, found in sun rays, makes T cells move faster — marking the first reported human cell responding to sunlight by speeding its pace.

T cells need to move to do their work, which is to get to the site of an infection and orchestrate a response. This study shows that sunlight directly activates key immune cells by increasing their movement. The researchers also noted that while production of vitamin D required UV light, which can promote skin cancer and melanoma, blue light from the sun, as well as from special lamps, is safer.

And while the human and T cells they studied in the laboratory were not specifically skin T cells, the skin has a large share of T cells in humans — approximately twice the number circulating in the blood. "We know that blue light can reach the dermis, the second layer of the skin, and that those T cells can move throughout the body," said a research team member.

The researchers also found that hydrogen peroxide was responsible for driving the motility response in T cells by activating a signaling pathway that increases T cell movement. Hydrogen peroxide is a compound that white blood cells release when they sense an infection in order to kill bacteria and to ‘call’ T cells and other immune cells to mount an immune response.

Sunlight makes hydrogen peroxide in T cells, which then makes the cells move. Meanwhile, an immune response also uses hydrogen peroxide to make T cells move to the damage site, said the research team. However, the researchers caution that there is much work to be done to understand the impact of these findings, but suggests that if blue light T cell activation has only beneficial responses, it might make sense to offer patients blue light therapy to boost their immunity.

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