Investigation into the impact of vitamin D supplementation on the microbiota of patients with and without ulcerative colitis.

Background: There is evidence vitamin D may be immunomodulatory and alter faecal microbiota, but results from clinical studies in humans to date have been inconclusive. This study aimed to assess the effect of vitamin D replacement in deficient patients with and without ulcerative colitis (UC) on inflammation and faecal microbiota.Methods: Vitamin D was replaced over 8 weeks to patients with active UC (defined by faecal calprotectin = 100 µg/g), inactive UC (faecal calprotectin < 100 µg/g), and non-IBD controls with baseline 25(OH) vitamin D < 50 nmol/L, and markers of inflammation and stool microbiota analysed. Results: Eight patients with active UC, 9 with inactive UC and 8 non-IBD controls received 40,000 units cholecalciferol weekly over 8 weeks. Mean baseline 25(OH) vitamin D increased from 34 (range 12-49) nmol/L to 111 (71-158) nmol/L (p < 0.001), with no difference between the three groups (p = 0.316). Faecal calprotectin levels reduced from median 275 to 111 µg/g (p = 0.023), platelet count reduced (p = 0.032), albumin increased (p = 0.044) in patients with active UC, but did not change in patients with inactive UC or non-IBD controls. No changes in overall bacterial diversity were noted although Enterobacteriaceae abundance increased overall (p = 0.028) and there was a trend towards a reduction in abundance of Ruminococcus gnavus (p = 0.068) following vitamin D supplementation in patients with UC. Conclusions: Vitamin D supplementation was associated with reduced intestinal inflammation in patients with active UC, but did not significantly alter faecal microbiota.