It is well known that vitamin D positively influences human health, but data on its impact on the human gut microbiome are lacking. Researchers conducted a pilot study on sixteen healthy volunteers. They were endoscopically examined to access a total of 7 sites to investigate the effects of oral vitamin D3 supplementation on the human mucosa-associated and stool microbiome, as well as CD8(+) T cells. Supplementation decreased relative abundance of Gammaproteobacteria including Pseudomonas spp. and Escherichia/Shigella spp. and increased bacterial richness. While no major changes occurred in the terminal ileum, appendiceal orifice, ascending colon, and sigmoid colon or in stools, the CD8(+) T cell fraction was significantly increased in the terminal ileum. Researchers concluded vitamin D3 modulates the gut microbiome of the upper GI tract, which might explain its positive influence on GI diseases such as inflammatory bowel disease or bacterial infections, and local effects of vitamin D demonstrate pronounced regional differences in the response of the GI microbiome to external factors.
Bashir M, et al. Effects of high djoses of vitamin D3 on mucosa-associated gut microbiome vary between regions of the human gastrointestinal tract. Eur J Nutr. 2016;55(4): 1479-89. doi: 10.1007/s00394-015-0966-2. Epub 2015 Jul 1.