ANAHEIM, CALIF. — Long-term daily supplementation with 1,200 mg elemental calcium protects against the development of adenomas and hyperplastic polyps, John A. Baron, M.D., reported at the annual meeting of the American Association for Cancer Research.
For up to 5 years after the end of a randomized, placebo-controlled clinical trial, patients who had received calcium supplementation had a 35% reduction in the risk of adenomas and a 41% reduction in the risk of hyperplastic polyps, said Dr. Baron of Dartmouth Medical School, Lebanon, N.H.
“Personally, I believe that calcium does reduce the risk of adenomas very clearly and probably reduces the risk of cancer itself as well,” he said. “There's one issue that needs to be resolved before calcium can be strongly recommended more generally, and that is that some people believe that calcium supplements may increase the risk of prostate cancer.”
Because of that issue, Dr. Baron said he would shy away from making broad recommendations. “For targeted recommendations for women, I think you could say that calcium is very likely to be effective and very unlikely to have significant toxicity, with the proviso that you'll probably need to take it for a long time before you see an effect on colorectal cancer.”
The original study randomized 930 patients with a history of precancerous adenoma to 1,200 mg of daily elemental calcium for 4 years or to a placebo. That study demonstrated a 19% overall reduction in polyp formation and a 28% reduction in advanced adenomas.
The current study reported on up to 8 years of follow-up data on these same patients after completion of the randomized controlled trial. Of the 865 subjects who survived the original trial, Dr. Barron and his colleagues obtained follow-up information on 822, and 597 had colonoscopies at least 6 months after the end of the trial.
The calculated risk reductions were adjusted for age, sex, study center, the interval between the final study exam and the first follow-up colonoscopy, and participants' reported use of calcium supplementation after the original study.
“We conclude that calcium supplementation is effective in reducing the risk of colorectal adenomas after the cessation of supplementation,” Dr. Baron said. “There's no rebound at all. In fact there appears to be a delayed, more pronounced suppression of colorectal neoplasia during the 5 years after treatment.”
He suggested that calcium may be exerting its effects at an early stage of the cancer process, and those effects only become manifest with a reduction in visible lesions years later.