The Vitamin D receptor is found in colon cancer cells. When Vitamin D binds to the receptor in the cancer cells, it may stop cancer cells from growing abnormally and may cause cell death. Vitamin D has been used in other research studies and information from those other research studies suggests that Vitamin D may help in the treatment of colorectal cancer.

In this research study, the investigators are comparing standard and higher dose Vitamin D treatment when given in combination with standard treatment for metastatic colorectal cancer. Standard treatment includes the chemotherapy combination of 5-FU, Leucovorin and Oxaliplatin (FOLFOX) with bevacizumab.