Does sunlight change our gut microbiome?

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Scientists show that ultraviolet (UV) light exposure leads to changes in the gut microbiome, but only in volunteers who were deficient in vitamin D.There is plenty of evidence that links vitamin D, the sunshine vitamin, to health outcomes.
Living at higher latitudes, which means less exposure to UV light and a greater chance of being vitamin D deficient, carries a higher risk of developing diseases such as multiple sclerosis (MS) and inflammatory bowel disease (IBD).
Research into the gut microbiome indicates that our microbial passengers may play a significant part in these conditions.
But what links vitamin D to our intestinal microbiota?
A team of researchers, many from the University of British Columbia, in Vancouver, Canada, set out to answer this question by studying how the gut microbiome responds to UV light.
When volunteers who were deficient in vitamin D received three sessions of UVB exposure, their gut microbiomes changed and bore the same hallmarks as those of study participants who were not vitamin D deficient.
The team published their findings in Frontiers in Microbiology.
The study included nine female volunteers who took vitamin D supplements in the 3 months leading up to the experiments and 12 who did not.
All participants had fair skin, specifically Fitzpatrick skin types 1 to 3.
The volunteers who had taken the supplements had vitamin D blood levels that are classed as adequate, while all but one of those who had not taken the supplements were vitamin D deficient.
All participants then had three sessions of full body exposure to UVB light. The research team saw increases in the vitamin D levels in all of the volunteers, as a result.
They then compared the composition of each participant’s gut microbiome before and after the treatments.
The authors found significant changes in the microbial compositions in the group that had been mostly vitamin D insufficient at the start of the experiment.
“Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements,” senior study author Prof. Bruce Vallance notes, summarizing the teams’ results. “UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.”