Background: Vitamin D deficiency has been associated with type 2 diabetes and inflammation, and more recently, with dysbiosis. Vitamin D supplementation has been shown to improve gut microbiome and intestinal inflammation in animal studies. It is proposed that vitamin D may exert actions on glucose metabolism and inflammation through the gut microbiome. However, limited human studies have investigated the effect of vitamin D supplementation on the gut microbiome.
Methods: In a double-blind randomised clinical trial, we compared effects of vitamin D supplementation (100,000IU loading dose of cholecalciferol followed by 4000IU daily) versus matching placebo for 16 weeks on faecal microbiome (16S rRNA sequencing;QIIME software) in 26 vitamin D-deficient (25(OH)D<50 nmol/L) overweight or obese, otherwise healthy adults. Data on physical activity, sun exposure, and diet were collected using validated questionnaires.
Results: There were no significant differences in physical activity, sun exposure, and diet (overall energy intake, fibre, protein, carbohydrate, total or saturated fat) between vitamin D and placebo groups at baseline and follow-up (all p>0.05). At baseline, the two groups did not exhibit any significant differences in microbiome profiles (p=0.9) or in diversity (p=0.6). At follow-up, there was no clustering based on vitamin D supplementation (p=0.3), however, there was a significant association between community composition and vitamin D supplementation at the genus level (p=0.04). The vitamin D group had a higher abundance of genus Lachnospira, and lower abundance of genus Blautia (linear discriminate analysis (LDA)>3.0).
Conclusion: Our findings suggest that vitamin D supplementation increases abundance of genus Lachnospira previously linked to decreased inflammation and insulin sensitivity, and decreases the abundance of genus Blautia linked to increased insulin resistance. Vitamin D supplementation may, therefore, have a beneficial impact on the faecal microbiome. Further studies are needed to explore whether improved microbiome following vitamin D supplementation would translate into improved clinical outcomes.