Protective effect of calcium in reducing colon cancer polyps lasts for years

04/07/05

Anaheim, Calif. -- Long term use of calcium supplements provides a protective effect that lasts for years against development of potentially precancerous colon polyps, researchers at Dartmouth Medical School say.

Their study, presented at the 96th Annual Meeting of the American Association for Cancer Research, found that patients in the treatment group of a randomized trial of calcium supplements had a 36 percent reduction in polyp formation in the five years after the end of the trial, compared to patients in the placebo group.

Although the researchers believe it is premature to recommend widespread use of calcium supplements for chemoprevention, they say their research is the second major study that shows the value of calcium in protecting people at risk of developing worrisome polyps.

"This provides further evidence of the potential of calcium to be used as a chemopreventive agent against development of colorectal cancer," says the study's lead author, Maria Grau, M.D., a research associate in the Section of Biostatistics and Epidemiology at Dartmouth. Co-author John Baron, M.D., a professor of medicine, will be presenting the results at AACR.

Calcium is the most abundant mineral in the body and is essential for the formation and repair of bone and teeth. It is known to play a role in such activities as nerve transmission, muscle contraction, and blood clotting.

It is also the only dietary substance that has been shown to be chemoprotective against development of colorectal polyps. The trial that proved that association, the Calcium Polyp Prevention Study, randomized 930 patients who had a history of developing precancerous adenoma to either 1200 mg. of elemental calcium supplements daily for four years, or to a placebo medication. Results demonstrated a statistically significant 19 percent overall reduction in polyp formation among participants who used the calcium supplements. The reduction in risk of advanced adenomas more worrisome polyps with a closer association with cancer, was even larger at 28 percent.

The findings being reported at AACR is a continuation of that study. The Calcium Follow Up Study was designed as an observational phase to track polyp formation in those who participated in the Calcium Polyp Prevention Study, as well as to look at the effect of additional use of calcium supplements among the participants.

The Dartmouth research team obtained information on 822 of the original subjects, including detailed records from follow up colonoscopies performed on 597 participants.

Even while adjusting for the use of calcium supplements after the primary study was over, the researchers learned that patients who had been randomized to daily use of the mineral during the trial had a significant reduction (36 percent) in the development of new adenoma polyps during the first five years post-study. There was even a larger effect for protection against development of non-neoplastic hyperplastic polyps - a 48 percent reduction of risk.

But they also found that the protective effect diminished over time. Over the entire follow-up period, which was as much as 10 years in some patients, the protective effect fell to a non-significant 19 percent in patients who had used the supplements in the study. Patients who used calcium supplements after the randomized trial had ended had a non-significant 15 percent reduced risk of developing polyps.

Calcium's long-term protective effect may be due to suppression of a precarcinogenic process that itself takes years to develop, Baron says, but adds that more study is needed to confirm that notion.

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