Metastatic (stage 4) colorectal cancer patients who were randomly assigned to the treatment arm of this study will be orally supplemented with high doses of vitamin D to achieve serum 25(OH)D concentrations of 200-250 nmol/L (80-100 ng/ml). Therefore, the supplementation dosage is not pre-set but will be determined on an individual basis. Vitamin D supplementation will be continued for 16 months, followed by a 12 month follow up period. Monthly monitoring of serum 25(OH)D and calcium levels will assure the safety of our treatment protocol. Subjects in the control arm of the study will be receiving standard cancer care at InspireHealth that includes supplementation with at least 2,000 International Units of vitamin D.
