Abstract

The recent worldwide rise in idiopathic immune and inflammatory diseases such as multiple sclerosis (MS) and inflammatory bowel diseases (IBD) has been linked to Western society-based changes in lifestyle and environment. These include decreased exposure to sunlight/UVB light and subsequent impairment in the production of vitamin D, as well as dysbiotic changes in the makeup of the gut microbiome. Despite their association, it is unclear if there are any direct links between UVB light and the gut microbiome. In this study we investigated whether exposing the skin to Narrow Band Ultraviolet B (NB-UVB) light to increase serum vitamin D levels would also modulate the makeup of the human intestinal microbiota. The effects of NB-UVB light were studied in a clinical pilot study using a healthy human female cohort (n = 21). Participants were divided into those that took vitamin D supplements throughout the winter prior to the start of the study (VDS+) and those who did not (VDS−). After three NB-UVB light exposures within the same week, the serum 25(OH)D levels of participants increased on average 7.3 nmol/L. The serum response was negatively correlated to the starting 25-hydroxy vitamin D [25(OH)D] serum concentration. Fecal microbiota composition analysis using 16S rRNA sequencing showed that exposure to NB-UVB significantly increased alpha and beta diversity in the VDS− group whereas there were no changes in the VDS+ group. Bacteria from several families were enriched in the VDS− group after the UVB exposures according to a Linear Discriminant Analysis (LDA) prediction, including Lachnospiracheae, Rikenellaceae, Desulfobacteraceae, Clostridiales vadinBB60 group, Clostridia Family XIII, Coriobacteriaceae, Marinifilaceae, and Ruminococcus. The serum 25(OH)D concentrations showed a correlation with the relative abundance of the Lachnospiraceae, specifically members of the Lachnopsira and Fusicatenibacter genera. This is the first study to show that humans with low 25(OH)D serum levels display overt changes in their intestinal microbiome in response to NB-UVB skin exposure and increases in 25(OH)D levels, suggesting the existence of a novel skin-gut axis that could be used to promote intestinal homeostasis and health.

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Excerpts:

The sun can indeed shine out of your backside, suggests research. Not because you’re self-absorbed, but because you’ve absorbed gut-altering UV radiation.

This is the first study to show that skin exposure to UVB light alters the gut microbiome in humans. Published in Frontiers in Microbiology, the analysis suggests that vitamin D mediates the change—which could help explain the protective effect of UVB light in inflammatory diseases like MS and IBD.

Exposure to UVB in sunlight is well-known to drive vitamin D production in the skin, and recent studies suggest that vitamin D alters the human gut microbiome. However, that UVB therefore causes gut microbiome changes, via vitamin D production, has so far been shown only in rodents.

In a new clinical pilot study, researchers tested the effect of skin UVB exposure on the human gut microbiome.

Healthy female volunteers (n=21) were given three one-minute sessions of full-body UVB exposure in a single week. Before and after treatment, stool samples were taken for analysis of gut bacteria—as well blood samples for vitamin D levels.

Skin UVB exposure significantly increased gut microbial diversity, but only in subjects who were not taking vitamin D supplements during the (winter) study (n=12).

“Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements,” reports Prof. Bruce Vallance, who led the University of British Columbia study. “UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.”

The results also showed some agreement with mouse studies using UVB, such as an increase in Firmicutes and decrease in Bacteroidetes in the gut following exposure.

Prof. Bruce Vallance: “The results of this study have implications for people who are undergoing UVB phototherapy, and identifies a novel skin-gut axis that may contribute to the protective role of UVB light exposure in inflammatory diseases like MS and IBD.”

https://m.medicalxpress.com/news/2019-10-sun-doesnt-skin-uv-exposure.html?fbclid=IwAR29Sk681AauWIeZW_O7EifmFxBA8_KVwoaKBkD6GANRZ64_5cUEltsBJXg

More information: Frontiers in Microbiology, DOI: 10.3389/fmicb.2019.02410 , https://www.frontiersin.org/articles/10.3389/fmicb.2019.02410/full

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