Taking vitamin D, calcium, or a combination of the two supplements, failed to prevent the recurrence of precancerous colorectal polyps in a large, randomized, placebo-controlled trial that followed patients for up to 5 years.
The negative findings came as a surprise because they contradict years of previous observational and animal studies suggesting a protective role for the supplements in preventing precancerous polyps, researcher John Baron, MD, of the University of North Carolina, Chapel Hill, and colleagues wrote in the Oct. 15 issue of New England Journal of Medicine.
According to the U.S. Centers for Disease Control and Prevention, 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.
The newly published study is among the first randomized trials to examine vitamin D’s role in the prevention of polyp recurrence and the largest to examine calcium’s role, Baron said.
“That was a big surprise. We thought we understood calcium because the data was really quite, quite strong,” said Dr. Baron.
He led the new study, published in Thursday’s New England of Medicine. The National Cancer Institute sponsored it and Pfizer Consumer Healthcare provided the pills.
It involved 2,259 people recently diagnosed with polyps, precancerous growths removed during colonoscopy. They were assigned to take either 1,000 international units of vitamin D3, 1,200 milligrams of calcium, both or neither. Women could choose to get calcium and then be given either real or dummy pills of vitamin D.
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.
“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.
The study was published in the Oct. 15 issue of the New England Journal of Medicine.