This is a one-year multi-centre, double blind, placebo controlled, randomized trial investigating oral vitamin D3 (Colecalciferol) as an add-on treatment to interferon-beta-1b for Multiple Sclerosis (MS). Not less than one month after initiation of therapy with interferon beta 1b, MS patients will be randomised to once weekly treatment with peroral colecalciferol capsules (Dekristol®, Swiss-Caps, Switzerland) containing 0.5 mg of vitamin D3, or to once weekly peroral treatment with matching placebo. The hypothesis is that vitamin D suppresses clinical and MRI activity of MS.

The patients will be examined clinically at baseline and at 6, and 12 months. Laboratory assessments will be performed at screening and 1, 2, 3, 6, 9 and 12 months after baseline. MRI will be performed (T1-weighted and T2-weighted) at randomization and 12 months thereafter. Sample size is 80 patients: two groups with 40 patients in each group. The primary statistical analyses will be based on the intent-to-treat (ITT) population which consist of all randomized patients who have started study medication. The primary efficacy variable MRI T2 BOD will be analyzed using ANCOVA with MRI T2 BOD at baseline as covariate. The incidence (with corresponding 95% confidence interval) of hypercalcaemia (mild, moderate and severe), laboratory abnormalities, dose adjustments, and significant adverse events will be calculated. The vitamin D status (proportion of patients with P-PTH <20 ng/l and S-OH(D)2 >85 nmol/l) at 6 and 12 months will be analyzed using logistic regression.

Inclusion Criteria:

• RRMS EDSS 0-5
• Betaferon used for at lest one month with positive MxA-response

Exclusion Criteria:

• hypercalcaemia
• kidney stones
• uncontrolled hypertension
• hypothyreosis
• peanut allergy
• severe depression
• sarcoidosis
• use of other IMD than interferon-beta