Exposure to sunlight can modify intestinal microbiome

Exposure of the skin to ultraviolet light from the sun can modify the intestinal microbiome according to a new study published in Frontiers in Microbiology. To mediate this change would be vitamin D and this would also explain the protective effect of ultraviolet light itself with regard to inflammatory bowel diseases.

It is well known that exposure to sunlight gives greater production of vitamin D in the skin. It is known, however, through studies published in recent years, also that the same greater quantity of vitamin D can alter the human intestinal microbiome. It follows that solar radiation on the skin can change the human intestinal microbiome but this has only been shown in rodents. This new study shows that this effect is also real for humans.

The researchers performed experiments on 21 healthy volunteer women. The 21 patients underwent three one-minute ultraviolet exposure sessions throughout the body for a week. Throughout the treatment, stool samples were taken and intestinal bacteria were analyzed. Blood samples were also taken to analyze vitamin D levels. The researchers discovered that the exposure of the skin to ultraviolet rays significantly increased the intestinal microbial diversity and this happened only in those people who had not taken vitamin D supplements in the course of experiments.

As explained by Bruce Vallance, a researcher at the University of British Columbia who led the study, exposure to UVB rays increased the richness and uniformity of the subjects’ microbiome. Before exposure to rays, women who did not take supplements showed a less diversified intestinal microbiome than women who already took vitamin D supplements. Among the bacteria that increased the most were the Lachnospiraceae, a genus of bacteria already previously linked with vitamin D.

“UVB light is able to modulate the composition of the intestinal microbiome in humans, through the synthesis of vitamin D,” says Vallance. Now researchers would like to discover the underlying causes but according to Vallance, it is likely that exposure to UVB light somehow affects the immune system of the skin and this, in turn, has a favorable influence on the intestinal environment for different species of bacteria.

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