The purpose of this study is to determine if vitamin D as an adjuvant therapy can improve the outcome (i.e. fewer relapses) and the quality of life, including levels of physical activity, in children diagnosed Crohn's disease (CD).

Crohn's disease is a chronic inflammatory condition affecting all segments of the digestive tract from the mouth to the anus. This condition is associated with an increased risk of relapses throughout the course of the disease. Nearly 25% of patients with Crohn's disease are in the pediatric age range. Many epidemiological data are in favor of an increase incidence of pediatric Crohn's disease. Environmental factors could explain this increased incidence. Among them sunlight exposure and vitamin D deficiency have been suggested by many authors.

Recent studies have described how varying doses of oral vitamin D supplementation can alter serum levels of 25 hydroxyvitamin D (25(OH)D), but no study has specifically addressed the question as to whether vitamin D supplementation can alter the rate of relapse/complications and/or quality of life in children diagnosed with CD.

Current treatments of CD at diagnosis are effective around the time of diagnosis, but in the short and long term, some of these therapies are inefficient or lead to allergic or intolerance reactions. Altogether the rate of relapses in the year after diagnosis is significant. Thus, different therapeutic approaches must be investigated with the aim of lowering the burden of the disease.

From November 2012 to July 2013, we conducted an open label pilot cohort study aiming to investigate the bioavailability and tolerance of high doses of vitamin D3 (3,000 IU or 4,000 IU per day) administered orally as an adjunct therapy in 20 children with newly diagnosed pediatric CD (http://clinicaltrials.gov/ct2/show/NCT01692808). Data from laboratory studies, observational research and pilot trials taken together suggest that vitamin D can be of great importance in the genesis and progression of CD. Vitamin D deficiency could be a true risk factor for disease occurrence and/or relapses. The results of our pilot study demonstrate that in children with active CD at diagnosis, a daily dose of 4,000 IU of vitamin D is well tolerated and quickly increases the blood levels of 25OHD3 to 100 nmol/L or above in 100% of children with CD at diagnosis. Moreover a maintenance dosage of 2,000 IU a day is required (and sufficient) for maintaining this target over several months. Currently there is no adequately powered study in the pediatric CD population exploring the relationship between vitamin D therapy at diagnosis and CD outcomes.

We propose a randomized controlled trial (RCT) to study the efficacy of high-dose oral vitamin D, as adjunct therapy, in children diagnosed CD, to reduce the relapse rate and to improve patients' quality of life.

Primary Efficacy End Point: The proportion of patient with at least one relapse 52 weeks after randomization.

Secondary efficacy endpoint: Quality of life scores, Cumulative steroid dose, Time to first relapse, Duration of corticotherapy, Number of relapses, Number of hospitalizations Safety Endpoint : incidence of hypercalcemia (defined as a corrected serum calcium level >2.65 mmol/L), incidence of hypercalciuria (defined as urinary calcium to creatinine molar ratio ≥1.50), incidence of supra-optimal levels of 25OHD3 as defined by a serum level ≥ 250 nmol/L, rate of study discontinuation due to hypercalcemia or hypercalciuria.

Efficacy Variable: Occurrence of relapse, Time to relapse, Change in QoL score from baseline to 26 weeks, 52 weeks. Change in physical activity score from baseline to 26 weeks, 52 weeks

Inclusion Criteria:

1. Age at randomization between 4 and 17 years inclusively
2. Pediatric Crohn's Disease Activity Index (PCDAI) ≤ 10 with no clinical symptoms (abdominal pain or blood in the stool) at inclusion
3. Receiving a stable dose for at least 4 weeks of any of the following drugs: Thiopurines, Methotrexate, or TNF-α inhibitors (Infliximab/Adalimumab)
4. Dosage of fecal calprotectin lower than 250 µg/g stool at inclusion.

Exclusion Criteria:

1. History of surgery resulting in a permanent colostomy or ileostomy (because of the inability to calculate PCDAI at baseline)
2. Patients who have already been included in the pilots vitamin D trials
3. Patients actively enrolled in other CD drug trials.

The vitamin D will be donated by a pharmaceutical company. It will be dispensed in anonymized bottles with the content similar in color and taste in order to keep patients unaware of their allocation. We will implement a number of study maneuvers aimed at minimizing measurement biases. These include: (1) masking of the data; (2) documenting the use of major co-interventions such as other multivitamin supplements.