Sunlight can boost your immune system

The best-known benefit of sunlight is that it boosts our body's vitamin D supply, but a new study has revealed that sunlight also energises T cells that play a central role in human immunity.

This study, published in the journal of Scientific Reports, showed that sunlight directly activates key immune cells by increasing their movement. "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 study's senior author Gerard Ahern from Georgetown University Medical Center in the US.

"Some of the roles attributed to vitamin D on immunity may be due to this new mechanism," Ahern added. The researchers 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. What drove the motility response in T cells was synthesis of hydrogen peroxide, which then activated 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.

And while the human and T cells the researchers studied in the laboratory were not specifically skin T cells -- they were isolated from mouse cell culture and from human blood -- the skin has a large share of T cells in humans, he says, 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," he says.

The researchers further decoded how blue light makes T cells move more by tracing the molecular pathway activated by the light. "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.

Ahern says there is much work to do to understand the impact of these findings, but he 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.