The Effect of Various Doses of Oral Vitamin D₃ Supplementation on Gut Microbiota in Healthy Adults: A Randomized, Double-blinded, Dose-response Study

Background/aim: To investigate the effects of vitamin D₃ supplementation on gut microbiota.

Patients and methods: Twenty adults with vitamin D insufficiency/deficiency [25(OH)D <30 ng/ml] were enrolled and given 600, 4,000 or 10,000 IUs/day of oral vitamin D₃ Stool samples were collected at baseline and 8 weeks for identifying gut microbiota using 16S rRNA gene amplification and sequencing.

Results: Baseline serum 25(OH)D was associated with increased relative abundance of Akkermansia and decreased relative abundance of Porphyromonas (p<0.05). After the intervention, we observed a dose-dependent increase in relative abundance of Bacteroides with a significant difference between the 600 IUs and the 10,000 IUs groups (p=0.027), and Parabacteroides with a significant difference between the 600 IUs and the 4,000 IUs groups (p=0.039).

Conclusion: Increased serum 25(OH)D was associated with increased beneficial bacteria and decreased pathogenic bacteria. A dose-dependent increase in bacteria associated with decreased inflammatory bowel disease activity was observed after vitamin D₃ supplementation.