Effects of vitamin D supplementation on intestinal permeability, cathelicidin and disease markers in Crohn’s disease: Results from a randomised double-blind placebo-controlled study

Randomized, double-blind, placebo-controlled trial in adults with Crohn's disease in clinical remission on stable therapy. The active intervention arm included 13 participants, with 14 in placebo, enrolled at Tallaght Hospital in Dublin, Ireland between October 2011 and December 2011.

Oral vitamin D3 2000 IU/day for 3 months, compared with placebo. Compliance in the active arm was greater than 95%.

Vitamin D3 increased 25(OH)D levels and was associated with higher LL-37, while intestinal permeability was maintained in the active group over 3 months. In placebo, small bowel permeability increased (p=0.018) and gastro-duodenal permeability increased (p=0.030). At 3 months, participants with 25(OH)D concentrations of 75 nmol/L or higher had higher LL-37, lower CRP (p=0.019), and higher quality of life (p=0.037), but between-group differences in CDAI, CRP, fecal calprotectin, and quality of life were not significant (p=0.119, 0.624, 0.140, 0.900). No adverse events or clinical relapses were reported.

Small sample size and short 3-month duration limit confidence in clinical effects. The study population was restricted to Crohn's disease patients in remission on stable therapy, which reduces generalizability. Several findings were within-group or subgroup associations rather than significant between-group differences in clinical outcomes.