effect of UV light on gut microbiome

New research shows that UV light exposure can affect the health of our gut microbiome. The results of this study impacts on individuals suffering from chronic inflammatory diseases such as IBD.

The multitude of microorganisms that live on and in human bodies, collectively known as the human microbiome have a significant impact on our health. The microbial cells in the human body is estimated to be nearly equal to number of human cells with the highest density of microbes present in the gut. The majority of these microbes live in symbiosis with the human body and are involved in various functions such as maintaining immunity against harmful pathogens, helping to digest food, and provide nutrients to our body.

The results from large scale projects such as the Human Microbiome Project and the MetaHIT (Metagenomics of the Human Intestinal Tract) project suggest an intimate link between our microbiome and our health. When the balance of microbial growth and diversity is impaired, which could result in loss of useful bacteria normally present, the condition is known as dysbiosis. Dysbiosis of the gut microbiome has been observed in patients with chronic infectious diseases such as inflammatory bowel disease (IBD). IBD refers to a group pf persistent and recurring gastrointestinal inflammations, which can occur anywhere along the entire GI tract or is restricted to only the large intestine. IBD causes relapsing diarrhea, fever, and abdominal pain. There is an increase in the increase of IBD occurrences with approximately 1.4 million and 2.2 million individuals afflicted in America and Europe respectively.

The important role of Vitamin D in IBD

In addition to the gut microbiome, vitamin D levels are also implicated in the development of IBD. Vitamin D deficiency is also linked to dysbiosis of the gut microbiota even in healthy individuals. About 80% of Vitamin D requirements in humans come from exposure to UVB rays in sunlight. People living in areas where sunlight exposure is limited to a few months in a year are at an increased risk of vitamin D deficiency. Thus, a causal relationship could exist between vitamin D deficiency and gut microbiome imbalance, which in turn is linked to inflammatory diseases such as IBD.

Research finds a link between gut microbiota and sunlight exposure

New research from Canada has shown for the first time the existence of a link between gut microbiota, sunlight exposure and vitamin D levels in humans. Research at the University of British Columbia, Canada reveals that exposure to UVB rays results in changes in gut microbiota. These changes were observed only in individuals who were vitamin D deficient. The results of this study is published in the journal Frontiers in Microbiology.

This pilot study included 21 healthy female participants; half of the participants had taken vitamin D supplements during the prior three months. All the participants were exposed to three 60-second full body exposure to UVB rays over a week. Blood and fecal samples were collected before and at the end of the study period to measure changes in vitamin D levels and gut microbiota.

UVB exposure improves microbiome

The participants who were vitamin D deficient showed an increase in gut microbial diversity. As explained by Prof.  Bruce Vallance, the lead researcher of the study, “Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements. UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.” Additionally, the vitamin D deficient participants also showed a 10% increase in vitamin D levels in their blood serum. This group of participants showed a significant increase in the relative abundance of Lachnospiraceae bacteria after UVB exposure. They also showed an increase in the relative abundance of Firmicutes and Proteobacteria and a decrease in Bacteroidetes. Prof. Vallance noted that “previous studies have linked Lachnospiraceae abundance to host vitamin d status. We too found a correlation with blood vitamin D levels, which increased following UVB exposure.”

These results along with the observed lack of changes in the vitamin D sufficient participants suggest that the UVB exposure mediates a change in the gut microbiome through vitamin D. As Prof. Vallance sums up, “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.”

This study does not aim to elucidate the exact mechanism by which vitamin D mediates changes in the gut microbiome. The researches hypothesize that the UVB exposure results in changes in the immune system locally, which then leads to more systemic changes including in the gut. This, in turn, changes the gut environment that promotes an increase in microbial diversity. This study is limited by the small and selective number of participants. Research that includes more participants with increased diversity will help to further validate the results shown in this study.

 

Written by Bhavana Achary, Ph.D

 

References:

Data on IBD – Kho ZY, Lal SK. The Human Gut Microbiome – A Potential Controller of Wellness and Disease. Front Microbiol. 2018;9:1835. Published 2018 Aug 14.

Bosman Else S., Albert Arianne Y., Lui Harvey, Dutz Jan P., Vallance Bruce A. (2019) Skin Exposure to Narrow Band Ultraviolet (UVB) Light Modulates the Human Intestinal Microbiome, Frontiers in Microbiology, 10, 2410 DOI=10.3389/fmicb.2019.02410

Press release – https://www.eurekalert.org/pub_releases/2019-10/f-wts101819.php

Image by Jill Wellington from Pixabay

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