Immune and inflammatory diseases such as inflammatory bowel disease (IBD) and multiple sclerosis (MS) have been linked with Western diets and environmental factors. One such environmental factor is reduced sunlight exposure, which leads to a decrease in vitamin D production, as well as dysbiotic changes in the makeup of the gut microbiome.
In a recent study published in Frontiers in Microbiology, scientists in Canada point out, “Limited UVB exposure is one of the most important environmental factors linked to the onset of immune mediated chronic inflammatory diseases, like IBD and MS.”
The intervention study, led by researchers from the University of British Columbia and the Women’s Health Research Institute in Vancouver, investigated whether repeated exposure of the skin to UVB light would alter the gut microbiota composition of healthy female volunteers.
The researchers studied 21 healthy Caucasian females between the ages of 19 and 40 with Fitzpatrick Skin Types I–III. The study examined whether increasing vitamin D levels by exposing the skin to UVB light would also change the makeup of intestinal microbiota.
The subjects were each given three one-minute sessions of full-body UVB exposure over the course of a week. Before and after treatment stool samples were collected for analysis of gut bacteria, and blood samples were also taken to measure vitamin D levels. Nine of the participants reported that they had been taking vitamin D supplements during the three months before the start of the trial , but the other participants had not. While most participants from the group taking vitamin D supplements before the study showed sufficient vitamin D serum levels, most of the subjects who had not taken them displayed insufficient vitamin D serum levels.
In one week, UVB exposures increased the gut microbiota diversity of the group that started the study with vitamin D insufficiency to the same level as that of the group that started the study with sufficient serum vitamin D levels. The exposure to UVB also had a selective influence on gut microbiota composition, as positive associations were found between organisms in the Lachnospira and Fusicatenibacter genuses and serum 25(OH)D levels.
“These findings suggest that otherwise healthy individuals carrying insufficient 25(OH)D serum levels have a less diverse microbiome composition as compared to individuals that are vitamin D sufficient. Also, UVB light exposures are able to increase the richness and evenness of the microbiome composition when given to VDS− individuals with a low starting microbial diversity,” the authors said.
UVB exposure may provide protection, benefit the gut
The study highlights how gut microbiota diversity only improved with UVB light exposure in the subjects who were not taking vitamin D supplements before the study—most of whom had a vitamin D insufficiency. This suggests how changes in the gut microbiota may depend on systemic levels of vitamin D measured by serum 25(OH)D concentrations.
"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,” said Professor Bruce Vallance, who led the University of British Columbia study. "In this study we show exciting new data that UVB light is able to modulate the composition of the gut microbiome in humans, putatively through the synthesis of vitamin D.”
Frontiers in Microbiology
2019; 10:2410. doi: 10.3389/fmicb.2019.02410
“Skin exposure to narrow band ultraviolet (UVB) light modulates the human intestinal microbiome”
Authors: E. Bosman, et al.