High Dose Vitamin D Study

The purpose of this study is to investigate the therapeutic effect and the safety of high-dose vitamin D supplementation in metastatic colorectal cancer patients. We propose to supplement metastatic (stage 4) colorectal cancer patients with oral doses of vitamin D to raise serum 25-hydroxy-vitamin D [25(OH)D] levels to the high normal range of 200-250 nmol/L. The primary objective of this study is to evaluate the metabolic consequences, including tolerability and toxicity, of prolonged, high-dose physiological vitamin D in patients with colorectal cancer. The secondary objective is to evaluate patient survival with regards to high-dose vitamin D supplementation.
Hypothesis:
Whereas low doses of vitamin D reportedly play a significant role in prevention of colorectal cancers, do much larger (pharmacological) doses of vitamin D have a significant therapeutic effect against the same kind of cancer?