Sunlight gives us more than vitamin D, a new study shows. Through a completely separate pathway, sunlight prompts immune cells called T cells to move more quickly through the body, helping them reach infected tissues faster.
“What we found is a completely separate role of sunlight on immunity," said the study's senior investigator, Gerard Ahern, PhD. "Some of the roles attributed to vitamin D on immunity may be due to this new mechanism."
Blue light from the sun is the specific component that makes T cells move faster, and it can reach through to the second layer of the skin, called the dermis. This explains how the skin successfully protects itself from the microorganisms that it frequently encounters. The skin has nearly twice as many T cells as there are circulating in the blood. Once the blue light from the sun reaches T cells living in the dermis, the newly energized cells then move on to circulate in the blood throughout the entire body.
Blue light is also safer for the skin than ultraviolet light, which is required for vitamin D production. Overexposure to ultraviolet light is associated with skin cancer and melanoma.
Ahern and his team studied the interplay between T cells and blue light by examining isolated T cells and their response to blue light. After being activated by blue light exposure, T cells are triggered to synthesize hydrogen peroxide, which then activates the signaling pathway responsible for the super-energized T cells.
White blood cells, including T cells, release hydrogen peroxide naturally during infection both to kill bacteria and to recruit other immune cells to the infection site to boost the immune response. After discovering the involvement of hydrogen peroxide in the studies with sunlight, Ahern said that the research “all fits together.”
Ahern’s findings contain the first report of a human cell responding to sunlight by increasing its speed, and in the future, therapy based on blue light could be used to boost the immune system.
The study was recently published in the journal Scientific Reports.