Staring at the Sun

UVB changes the gut microbiome

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The Sun is the center of our solar system. It makes up 99.8% of the mass of the whole solar system and is responsible for Earth’s climate and weather. With an average radius 695,508 km of which 20–25% is the core, the Sun is 109 times wider than the Earth and 330,000 times as massive, with a surface area of 11,990 times that of the Earth’s. 

In the past, the Sun has motivated mythological stories, such as the ones of the ancient Chinese, Egyptians,  Aztecs, or even Native American. Today, we know the importance of the light exposure for vitamin D production, and its role against several diseases (e.g. cancer, depression, bone fractures, influenza, and type-2 diabetes). 

Now, the Sun has inspired researchers from Canada to develop a pioneer study, in which a relation between UVB light and changes in the gut microbiome is demonstrated. The authors explain that the exposure to narrow band-UVB significantly increases alpha and beta varieties of vitamin D, in the group not taking any vitamin D supplements. Furthermore, bacteria from several families augmented, after the UVB exposure. Several microorganims were involved in this microbiome modification, and further analysis revealed a correlation with the relative abundance of Lachnopsira and Fusicatenibacter genera. Importantly, the work suggests the existence of a novel skin-gut axis that might stimulate intestinal homeostasis and health.

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.


Else S. Bosman et al., Skin Exposure to Narrow Band Ultraviolet (UVB) Light Modulates the Human Intestinal Microbiome, Frontiers in Microbiology, 2019.

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Harvard School of Public Health Nutrition Source. Vitamin D and health. Available from:



Celia Fortuna Rodrigues

PharmD, PhD , University of Porto


Go to the profile of Josef Wagner
Josef Wagner 12 months ago

Well done Celia, I really like the association between sun and the gut microbiome. 

Vitamin D turns out to be more a more one (the) of the most important vitamins for human and most likely for animal too. 

Looking forward to here more from you


Go to the profile of Celia Fortuna Rodrigues
Celia Fortuna Rodrigues 12 months ago

Yes, I agree. The authors of this study did a really great job :)