COMMENTARY

Some Benefits of Sunlight May Be Independent of Vitamin D

JoAnn E. Manson, MD, DrPH

Disclosures

January 18, 2017

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Hello. This is Dr JoAnn Manson, professor of medicine at Harvard Medical School and Brigham and Women's Hospital. I'd like to talk with you about a very interesting and intriguing study that was recently published in Scientific Report[1] by researchers at Georgetown Medical Center, suggesting that sunlight exposure may boost immune function through mechanisms that are completely separate from vitamin D. The study suggests that blue light specifically, within the visible light spectrum, may directly activate key immune cells and increase their motility. The researchers studied both human and mouse T lymphocytes after exposure to blue light. They found that the blue light triggered the synthesis of hydrogen peroxide, which in turn activated key signaling pathways that led to increased movement and motility of the T cells.

This is a process that can take place naturally. When T cells are stimulated by infection or the presence of a foreign invader, they will release hydrogen peroxide, and this will mobilize other T cells and other immune cells to mount an immune response. So it seems very biologically plausible that blue light could be having this effect, which can be replicated by exposing the T cells directly to hydrogen peroxide.

Why is this of particular interest? Blue light is known to reach the dermis, the second layer of the skin, and the dermis has a very high concentration of T lymphocytes. In fact, it's been estimated that there are twice as many T lymphocytes in the dermis as circulating in the bloodstream. When mobilized, these T lymphocytes can travel through the dermis and into the bloodstream. This suggests that there may, indeed, be a separate pathway through which sunlight exposure (specifically blue light exposure) may affect immune function.

Vitamin D may do so as well. It's known that exposure to UVB light stimulates the synthesis of a precursor of vitamin D in the skin. The concern has been that recommending increased sun exposure to increase the blood level of vitamin D may lead to increased risk for skin cancer and skin aging, because of the effect of UVB light. UVA light also has the effect of increasing skin aging.

The National Academy of Medicine actually did not recommend increasing sun exposure to boost levels of vitamin D. However, this pathway through blue light may be attainable through the use of special lamps that would deliver blue light, which would reach the derma without posing increased risk for skin cancer or skin aging.

This is a very exciting area of research. I hope it will continue. Stay tuned for more results in the future along these lines. Also stay tuned for the results of the large-scale randomized trials of vitamin D supplementation, including our vital vitamin D and omega-3 trial. The findings from several large-scale randomized trials of vitamin D throughout the world should be available within the next 1 to 1.5 years. Thank you so much for your attention. This is JoAnn Manson.

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