Previous research suggested that high levels of vitamin D would protect people against colorectal cancer. People with high blood levels of this hormone/vitamin were more likely to survive. A big observational study in Europe called EPIC had found that those with high blood levels of vitamin D were less likely to be diagnosed with colorectal cancer. No one had done a study that showed whether taking vitamin D supplements would be protective, however.
Now, a study including more than 2,000 people has shown that vitamin D and calcium supplements, either alone or together, did not reduce the chance of a recurrence of colorectal adenoma, a growth that may progress to a tumor. All of these people had had adenomas detected during a colonoscopy, putting them at high risk for a recurrence of adenoma. Since these growths can progress to cancer, this group is at high risk for colorectal cancer.
Vitamin D and Calcium Supplements:
The participants were randomly assigned to get 1,000 IU of vitamin D or 1200 mg of calcium daily, both nutrients or two placebo medications. They had a follow up colonoscopy three to five years after starting the study. The investigators were disappointed to discover that the vitamin D and calcium supplements made no noticeable difference in the risk of adenoma. The conclusion is that there is little or no likelihood that such supplements will reduce the risk of colorectal cancer.