Mounting research confirms that sun avoidance may be at the heart of a large number of health problems. Not only does your body produce vitamin D in response to sun exposure on bare skin, but sunlight also produces a number of other health benefits that are unrelated to vitamin D production.

In fact, humans appear to have a lot in common with plants in this regard — we both need direct sun exposure in order to optimally thrive, and while artificial lighting sources offering specific light spectrums may be helpful for various problems, ideally we need the full spectrum of light that natural sunlight offers.

Most recently, researchers at Georgetown University Medical Center (GUMC) published a laboratory study using cells in petri dishes, showing that exposure to blue and ultraviolet (UV) light increases T cell activity — white blood cells involved in immune function and fighting infections.^1,2,3

Sunlight Is a Natural Immune Booster

This is thought to be the first study showing an impact of light on this particular type of immune cell, so more research is needed to verify the results. However, there's plenty of evidence in the medical literature confirming that sunlight has immune-boosting properties.

In this study,⁴ light was found to stimulate the production of hydrogen peroxide, which boosted the activity of T lymphocytes. As little as five to 10 minutes of sun exposure were needed to boost immune cell activity. As noted in one news report:⁵

"Given the large surface area of human skin, all of the T cells present in skin could potentially benefit from this phenomenon through exposure to blue light, the researchers suggest.

Note that vitamin D is only produced in the body via exposure to UVB rays, which can be harmful in cases of prolonged sun exposure.

If blue light from the sun's rays is capable of energizing infection-fighting T cells, it could be a potential means of treatment for boosting immunity in many patients, the researchers conclude."

While the researchers appear hopeful that blue light alone might be a valuable immune-boosting treatment, it's important to realize that the biological effects of light can be very complex, and it's important to get it right.

As explained by Dr. Alexander Wunsch, a world class expert on photobiology, excessive exposure to blue light — such as that from LED lighting, which is primarily blue and devoid of near-infrared found in sunlight and incandescent lighting — can be quite harmful, and may be a significant risk factor for age-related macular degeneration (AMD).

The healthiest blue light is from the sun, as it is balanced by near-infrared radiation, which has many important biological functions. Importantly, near-infrared radiation will activate cytochrome C oxidase in your mitochondria and help to optimize ATP production.

T Cells Are Intrinsically Photosensitive

For a long time, it was believed mammals only had photosensitive cells in the eye. We're now finding photosensitive cells in many other areas of the human body.

As noted by the authors, this study demonstrates that "T lymphocytes possess intrinsic photosensitivity and this property may enhance their motility on skin." In other words, T cells sense and respond to light.

Blue light specifically triggers the production of hydrogen peroxide (H2O2) in T cells, which triggers a chemical cascade that results in increased T cell motility. The increased motility or activity, in turn, allows the immune cells to function better.

Interestingly, once the T cells are activated they also alter their antioxidant capacity — an effect that appears to allow for greater H2O2 production in response to light.

The spectral sensitivity of T cells peaked at both ~350 nanometers (nm), which is in the ultraviolet A (UVA) range, and ~470 nm, which is in the blue spectrum. The latter (470 nm light) has previously been shown to kill methicillin-resistant Staphylococcus aureus (MRSA) in vitro.⁶

According to lead author Gerard Ahern, Ph.D., an associate professor at the Department of Pharmacology and Physiology in Georgetown, some of the immunity benefits typically attributed to vitamin D may actually be due to this new-found mechanism.

While there may be some truth to that, previous research has teased out a number of different mechanisms for vitamin D's activity, including its bactericidal and immune-boosting effects.

For example, researchers have found vitamin D acts directly on the beta defensin 2 gene (which encodes an antimicrobial peptide) and the NOD2 gene (which alerts cells to the presence of invading microbes).⁷ Vitamin D is also involved in the production of over 200 antimicrobial peptides that help fight all sorts of infections.