A small, open label study in Austria looked at the effects of a high dose Vitamin D supplement (a weekly dose of 980 IU/kg bodyweight for 4 weeks, followed by 4 weeks at 490 IU/kg) was given to 16 healthy volunteers. All participants underwent gastroduodenoscopy and colonscopy before and after the intervention. Biopsies were taken throughout the gastrointestinal tract and stool samples were retained and analysed. The microbial population was characterised in each part of the gut. In addition, the number of CD8+ T cells was enumerated as they show the highest expression of the Vitamin D receptors (VDRs). In this manner, the study was able to comment on changes in the total gut microbiome.
Sufferers of Irritable bowel disease (IBD) are often deficient in Vitamin D (2). The study authors suggest that having sufficient levels of Vitamin D in the diet might help avoid the onset of such autoimmune diseases.
The high dose intervention (which was above most recommended levels of supplementation) resulted in mean Vitamin D levels of 55.2 ng/mL in the volunteers. No adverse effects were noted.
Following the intervention, there were major shifts in the bacterial population of the upper gastrointestinal tract, but not in the lower gut or stool samples. The CD8+ T cell fraction was significantly increased in the terminal ileum.
In the upper gut, there was major reduction in Gammaproteobacteria, which includes the opportunistic pathogens, Pseudomonas spp and Escherichia/Shigella spp. These bacterial usually prosper in an inflammatory environment. When the inflammation is removed, beneficial bacteria such as Bacteroides spp. are able to prosper.
Three of the volunteers were infected with Helicobacter pylori, which is a common cause of gastrointestinal ulcers. This single species accounted for 90 percent of the bacteria in their stomachs. However, the overall abundance of Helicobacter spp in the gut was reduced following the intervention.
In summary, this small study indicates that Vitamin D intervention should be able to positively modulate the microbiome in the upper human gastrointestinal tract.