Previous studies suggested that increased vitamin D and calcium intake helps prevent the recurrence of colon cancer. However, a new study challenges this claim, saying that vitamin D and calcium do not stop the growth of colon polyps at all.
"It suggests that you should not think you should take calcium or vitamin D to reduce your risk of colon cancer," study co-author Elizabeth Barry, assistant professor of epidemiology and community and family medicine at Dartmouth's Geisel School of Medicine, told Health Day.
To determine how vitamin D and calcium affect cancer, the researchers studied 2,259 patients who went through complete colonoscopy and successfully had all colorectal polyps removed. They were all expecting to have a follow-up colonoscopy in three to five years.
The participants were divided into groups, one of which was given vitamin D, another calcium carbonate, and another vitamin D plus calcium carbonate. All groups took the vitamin D and calcium carbonate daily. One group served as control and was not given anything.
During the participants' follow-up colonoscopy, 43 percent of them were found to have one or more adenomas. Compared to the placebo group, the groups that took vitamin D and calcium, or both, did not have a decreased risk for recurring polyps.
Lead study author Dr. John Baron, professor of medicine at the University of North Carolina School of Medicine, said that he was surprised that calcium, which is known to prevent cancer, did not prevent the growth of colon polyps.
"Daily supplementation with vitamin D3 (1000 IU), calcium (1200 mg), or both after removal of colorectal adenomas did not significantly reduce the risk of recurrent colorectal adenomas over a period of 3 to 5 years," the researchers wrote.
Colon cancer is the number two cancer killer in the U.S. The risk for colorectal cancer increases as a person ages; over 90 percent of people with colon cancer are 50 years old or more. Studies have suggested that the risk for developing colorectal cancer can be reduced by having a low-fat, high-fiber diet, doing regular exercise and avoiding alcohol consumption, according to the U.S. Centers for Disease Control and Prevention.
The study was published in the Oct. 15 issue of the New England Journal of Medicine.