Sunlight on the abdomen: Crucial for GI microbiome composition?

You’re lying on a blanket on the beach wearing a bathing suit, abdomen exposed to direct sunlight. With your midsection basking in sunlight, could you be triggering shifts in your gastrointestinal (GI) microbiome?

Vitamin D is, of course, activated by UV wavelengths on the skin, and thereby introduces beneficial changes in intestinal health with effects that include increased intestinal immunity, increased thickness of the mucus barrier, and reduced intestinal permeability, important and, in many instances, life-changing effects. But there is more to sunlight exposure than just UV light.

Recall from my recent discussions on light management that, while ultraviolet (UV) light only penetrates <1 millimeter into the epidermis (but sufficient to activate vitamin D) of the skin, red and especially infrared (IR) light wavelengths penetrate a centimeter or more, with higher wavelengths farther into the IR spectrum able to penetrate deep into body structures. IR wavelengths can therefore penetrate abdominal skin, fascia (connective tissue), abdominal fat, intestinal walls, and perhaps the microbes dwelling within. As you lay on the beach and enjoy the sun, IR light therefore has potential to exert effects on the GI microbiome. Emerging evidence in both animals and humans suggest that IR light shone on the abdomen also exerts effects elsewhere on the body such as the retina and brain (so-called abscopal effects, or effects distant from the irradiated site of exposure).

Evidence suggests that, yes, infrared exposure of the abdomen causes changes in microbial composition of the GI microbiome: increases in butyrate-producing (“butyrogenic” species) such as Akkermansia, Faecalibacterium, and Allobaculum, while reducing potential Proteobacterial pathogens (fecal species). IR light on the abdomen appears to add to these effects through mostly favorable shifts in microbial species composition.

Even more interesting, emerging experimental evidence also suggests that infrared light shone on the abdomen reverses—not reduces, but reverses—the deposition of beta-amyloid plaque and phosphorylated tau proteins in the brain, the two hallmarks of Alzheimer’s dementia. Witness these microscopic sections of brain tissue in mice:

From Chen et al 2021

The leftmost column labeled “Ctrl M” are brain sections from control mice unexposed to IR light. In the third column from the left labeled “PBM 730” (signifying photobiomodulation with 730 nm infrared light) are brain sections from mice exposed to infrared. You can see that the brightly red-stained beta-amyloid plaque is absent from the PBM 730 mice. Along the bottom row, you can also see the absence of bright green-colored staining for phosphorylated tau. Both were eliminated by abdominal exposure to infrared light.

Key in these phenomena is that infrared wavelengths are able to pentetrate deep into the body. UV, blue, and visible light do not have this capability; only IR does. Given human evolution under a tropical sun, life outdoors with little to no clothing, was abdominal exposure to IR wavelengths one of the factors that “molded” the composition of the gastrointestinal microbiome and its effects on health? Conversely, is the ubiquity of dysbiosis and SIBO in people with obesity due to the excess subcutaneous and abdominal fat that reduces IR penetration into the GI microbiome?

As I have often warned, as interesting as these findings are and the potential they have for even greater amplification of health, you cannot do any better than exposure to sunlight. These insights therefore hold greatest potential for those of us who live in northern climates where sunlight is weak or concealed behind clouds, or those of us who spend our days working indoors unexposed to sun. If you live in a sunny climate such as southern California, Florida, Arizona, or Texas, then just get outside every day, making it a point to include exposure of the abdomen. Another issue to consider: If you have a significant quantity of abdominal subcutaneous (below the skin) and visceral (within the abdomen) fat, have you set yourself up for deprivation exposure to the GI microbiome and thereby all the health risks of such deprivation?

If you feel that you may benefit from red/IR exposure, please do not purchase red light devices costing thousands of dollars. Because red light manufacturers count on consumer ignorance of the science, they are ready and willing to sell you expensive devices complete with extravagant claims. An inexpensive device costing <$100 is all you need to expose your abdomen, face, and (with eyes closed) retina and enjoy both local and abscopal effects.

The original IHB post is currently found on the: ⎆Infinite Health Blog, but accessing it there can require an unnecessary separate blog membership. The copy of it above is complete, and has been re-curated and enhanced for the Inner Circle membership.