Research Finds A New Link Between Sun Exposure & Gut Health

You religiously slather on sunscreen, wear a floppy hat even when you aren't at the beach, and seek shade whenever you're outside, all in an effort to avoid sun exposure. We all know the dangers of UV: skin damage, wrinkles, and skin cancer have all been linked to the sun's rays. 

But have we taken it too far? Researchers believe our sun-safe behavior may be driving not only vitamin D deficiencies but inflammatory bowel disease and gut issues. Yup—a new study found a surprising link between sun exposure and gut health.  

In the study1, published in Frontiers in Microbiology, 21 healthy women had their vitamin D levels and microbiome tested and then were exposed to UVB light three times over the course of a week. The study was conducted in Canada during the wintertime, so the women were not exposed to UV rays outside of the experiment; however, some of the women reported supplementing with vitamin D prior to the study.

As expected, vitamin D levels increased across most of the participants. Interestingly, participants who were the most deficient in vitamin D at the start of the study also saw a significant increase in microbial diversity along with vitamin D levels. Microbial diversity is associated with good gut health, especially the specific strains observed in the study. 

That doesn't mean you should ditch sunscreen in favor of gut health, though. The participants who had sufficient vitamin D status at the start of the study (specifically those who used vitamin D supplements) had more diverse microbiomes to begin with. Study authors noted that UVB exposure increased gut diversity in those who had low-vitamin-D status to the same level as those who had sufficient status. This points to the importance of maintaining good vitamin D levels for gut health, no matter whether you get it from UV light or a supplement.

Previous research has noted an association between low vitamin D levels and autoimmune disorders2, like IBS, but this is the first study to demonstrate the link between sun-exposure-induced vitamin D levels and increased gut biodiversity, which means the gut-skin axis could be the key to developing targeted therapies for gut disorders in the future.