The study, published Thursday (Jan. 14) in the New England Journal of Medicine, involved a four-year follow-up of 832 patients who had polyps removed. Doctors consider polyps in the colon, also called colorectal adenomas, a strong precursor to cancer.

Researchers found 31 percent of 409 patients randomly selected to receive 1200 milligrams of calcium carbonate daily developed one or more polyps during the study. Thirty-eight percent of 423 volunteers who received an inactive compound, or placebo, showed new polyp growth.

"In the treatment group, we found overall a 24 percent decrease in the number of polyps and a 19 percent decrease in the risk of recurrence," said Dr. Robert Sandler, professor of medicine at the University of North Carolina at Chapel Hill School of Medicine. "This represents a significant, although moderate, reduction in the risk of recurrent colon adenomas."

A chief researcher in the study and co-director of UNC-CH's Center for Gastrointestinal Biology and Disease, Sandler praised calcium supplements as safe and probably somewhat effective in preventing colon cancer and slowing osteoporosis.

"People who have had adenomas in the past still need to have regular colon examinations by their physicians," he said. "We need more research on preventing colon cancer because this work is not the final answer."

Patients were treated at six clinical centers at the Cleveland Clinic Foundation, the Dartmouth-Hitchcock Medical Center and the universities of Iowa, Southern California, Minnesota and North Carolina. Dr. John Baron of Dartmouth-Hitchcock was overall study director.

"Colon cancer is a big problem in the United States," Sandler said. "It is the second leading cause of cancer deaths. This year we expect 67,000 new cases in women and 65,000 new cases in men."

Physicians believe 90 percent or more of colon cancers evolve from polyps, he said. Earlier animal research and observational studies in humans suggested that calcium might lower the risk of colon polyps and cancer. The new study did not directly address the questions of whether calcium supplements affect polyps changing to invasive cancer but is still good news.

Diets rich in vegetables and fruits also have been associated with lower risks, while diets high in animal fat and red meat seem to boost the chance of cancer.

Patients, three-quarter of whom were men, averaged just over age 60. The National Institutes of Health supported the new study.

Note: If no author is given, the source is cited instead.

• Colon Cancer
• Osteoporosis
• Gastrointestinal Problems
• Women's Health
• Diseases and Conditions
• Breast Cancer

• Colorectal cancer
• Metastasis
• Hormone replacement therapy
• Gallstone
• Vitamin D
• Osteoporosis