Calcium Seems to Protect Against Colorectal Cancer
Supplements effective at reducing polyps that can lead to tumors, study says
By Kathleen Doheny
TUESDAY, June 15 (HealthDayNews) -- Taking calcium supplements helps prevent polyps in the colon, a risk factor for colorectal cancer.
And the supplements seem to offer the most protection against the advanced polyps most strongly associated with invasive colorectal cancer, according to a new study.
"In an earlier publication, we showed a reduction in polyps [with calcium intake]," said Dr. John A. Baron, a professor of medicine at Dartmouth Medical School, and senior author of the study that appears in the June 16 issue of the Journal of the National Cancer Institute.
"There was less than a 20 percent reduction, overall," he added. "Now, we find when we look at more advanced [polyps], it is a much more marked reduction, suggesting that calcium might have a more pronounced effect in preventing advanced [polyps]."
For advanced polyps, calcium might reduce the risk of colorectal cancer 35 percent to 45 percent, Baron said.
An estimated 106,370 new cases of colon cancer and 40,570 cases of rectal cancer will be diagnosed this year in the United States, according to the American Cancer Society, and about 56,730 deaths will result.
Most colon and rectal cancers begin as a polyp, a growth of tissue into the center of the colon or rectum. Removing polyps, also known as adenomas, early may prevent them from becoming cancerous, according to the Cancer Society.
In new the study, Baron's team analyzed data from 913 patients enrolled in the Calcium Polyp Prevention Study. Patients took either a 1,200 milligram supplement of calcium or a placebo, and had a follow-up colonoscopy -- an exam of the colon -- one and four years after they began the calcium therapy.
Compared with those on a placebo, people taking calcium supplements had fewer of all types of polyps. But the protective effect was most pronounced for the kind of advanced lesions that are most strongly associated with colon cancer. The risk for advanced polyps was reduced by about 35 percent, Baron said.
While it's not known exactly how the calcium may help prevent the polyps, researchers speculate that calcium prevents the irritating and cancer-promoting effect of bile acids and other fats in the bowel.
In an accompanying editorial in the journal, Ulrike Peters, now an assistant faculty member at the Fred Hutchinson Cancer Research Center in Seattle, but formerly a research fellow at the National Cancer Institute, writes that the beneficial effects of calcium supplements still have not been proven. But the protective role of calcium against colon cancer "looks very promising," she said.
For now, she added, those wanting to reduce their risk of colon cancer should follow the dietary recommendation for calcium -- 1,200 milligrams a day for those over 50 years of age, and 1,000 milligrams for those 19 to 50.
"We cannot really tell if there is a difference right now between [calcium from] supplementation and from food," she said. "That needs further investigation.
Dr. Arthur Schatzkin, lead author of the editorial and chief of the nutritional epidemiology branch of the NCI, agreed. "For a variety of health reasons people should try to make sure they are getting adequate intakes of calcium." Calcium helps with bone strength, for one thing. But he cautioned that "...we haven't proved that calcium prevents colon cancer."
Added Baron: "As always, talk to your doctor. It is really thought that calcium supplements are safe, but don't think you can take something like this and forget everything else. Remember, this is just one aspect of what might be done."
He advised people to get colorectal cancer screening tests, such as colonoscopies and occult blood testing. "Exercise is probably beneficial," he added, in helping to reduce colorectal cancer risk.
To learn more about colorectal cancer, visit the National Cancer Institute.
SOURCES: John A. Baron, M.D., professor of medicine, Dartmouth Medical School, Lebanon, N.H.; Ulrike Peters, Ph.D., formerly research fellow at the National Cancer Institute, now assistant faculty member, Fred Hutchinson Cancer Research Center, Seattle; Arthur Schatzkin, M.D., D.P.H., chief, nutritional epidemiology branch, National Cancer Institute, National Institutes of Health, Bethesda, Md.;
June 16, 2004, Journal of the National Cancer Institute
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