Relationship between Vitamin D status and microbiome changes in Bulgarian patients with type 2 diabetes mellitus

The human microbiome plays a very important role in the normal functioning of both metabolic and immune systems. Changes in gut microbiota (dysbiosis) possibly contribute to the development of metabolic and autoimmune diseases. There is close association between the human gut microbiome and Vitamin D metabolism. The objective of our study was to characterize the composition of the gut microbiome in patients with type 2 diabetes mellitus (T2DM) in comparison to controls with normal glucose tolerance, and to correlate the Vitamin D status with the changes in the gut microbiome. Totally, 15 patients with T2DM and 16 controls were enrolled in the study. The complex gut microbiome was analysed by next generation sequencing (NGS) in both groups, additionally divided into subgroups according to serum 25-hydroxyVitamin D (25[OH]D) levels. We found a significant decrease in butyrate-producing bacteria Eubacterium spp. and an increase in lipopolysaccharide (LPS) - positive bacteria Enterobacter spp., Escherichia spp. and Pseudomonas spp. in T2DM patients compared to controls. Control individuals with 25[OH]D levels of over 80 nmol/L were characterized with significantly decreased amount of Escherichia spp. and Pseudomonas spp. and increased Eubacterium spp. On the other hand, 25[OH]D < 80nmol/L levels in diabetic patients were related with lower content of butyrate-producing bacteria and higher levels of LPS-positive bacteria. The results showed an influence of gut microbiome on the glucose homeostasis and a relationship between Vitamin D levels and the gut microbiome.