Vitd and Barrier Function in IBD

Inclusion Criteria: * All patients must fulfill the clinical criteria for diagnosis of CD as defined by Lennard-Jones et al. (1976) * All patients must be in clinical remission for at least 1 month at study entry as defined by a Crohn's Disease Activity Index (CDAI) of \<150 * 18-65 years * Patients on stable drug therapies for at least 1 month pre-enrolment * Sufficient English language ability to carry out the study requirements Exclusion Criteria: * Symptomatic CD at study entry including CDAI \>150 * Pregnancy * Previous extensive small bowel resection (less than 200 cm of viable small bowel or a loss of 50% or more of the small intestine) * Presence of an ileostomy or colostomy * Known hypersensitivity to vitamin D * Hypercalcaemia (corrected serum calcium \> 2.66 mmol/L) * Those currently using supplemental vitamin D \>800 IU/D * Diagnosis of any of the following: active tuberculosis, sarcoidosis, hyperparathyroidism, renal failure, pseudohyperparathyroidism, malignancy, active, lymphoma, short bowel syndrome * Antibiotic use in the 4 weeks prior to enrolment * Current use of bisphosphonates * Renal Impairment, Diabetes Mellitus * Patients participating in a concurrent RCT * Alcohol dependency