By TAP Integrative

More than 1,000 microorganisms make their home in the human gut. This collection of bacteria, fungi and viruses is called the microbiome. The microbiome is involved in many aspects of human health – from protecting against pathogens to affecting immunity and metabolism. Studies are continually adding to our understanding of the microbiome’s role in human health, as well as how it is affected by diet, genetics, medications and nutritional supplements.

One widely studied nutrient whose effects on the microbiome have not been elucidated is vitamin D. Known for its effects on bone mineralization and the modulation of the immune system, vitamin D has been shown in numerous studies to have a positive effect on health. In a paper published in 2016 in the European Journal of Nutrition, researchers aimed to describe the effects of oral vitamin D3 supplementation on the microbiome.

In an interventional, open-label pilot study of 16 healthy volunteers, the researchers endoscopically collected stomach, small bowel, colon and stool samples before and after 8 weeks of supplementation with vitamin D3. For the first 4 weeks, participants received a weekly dose of 980 IU/kg bodyweight. For the second 4 weeks, the weekly dose was reduced to 490 IU/kg bodyweight. Samples collected were assessed for bacterial composition.

The results showed that the regimen of vitamin D3 supplementation changed the gut microbiome in the upper gastrointestinal tract—decreasing the relative abundance of Gammaproteobacteria, including Pseudomonas spp. and Escherichia/Shigella spp., and increasing bacterial richness. Additionally, vitamin D3 supplementation resulted in significantly increased CD8+ T cell immunity in the terminal ileum.

The study’s authors conclude that vitamin D3’s ability to modulate the upper GI microbiome and immunity in the terminal ileum may explain why it has a positive effect on gastrointestinal disorders.


Bashir M, Prietl B, Tauschmann M, et al. Effects of high doses of vitamin D3 on mucosa-associated gut microbiome vary between regions of the human gastrointestinal tract. Eur J Nutr. 2016;55(4):1479-1489.

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease