March 9, 2001 -- Chalk up another win for calcium? In addition to treating heartburn and helping prevent bone loss, calcium supplements may also help reduce the spread of growths that could turn into colorectal cancer in people at risk for developing the disease.
But you may want to wash the pills down with water rather than chase them with a high-fat milkshake, because they seem to work best as part of a healthy diet, say Israeli researchers in a recent issue of the journal Cancer.
Adenomas, more commonly known as polyps, are small, benign tumors that are outgrowths of the tissue that line the walls of the lower bowel. Most colorectal cancers arise from these nonmalignant growths, cancer experts say.
The researchers gave an over-the-counter calcium supplement to 33 patients with rectal adenomas and followed them for one year, along with 19 additional adenoma patients who did not take extra calcium. All the participants were questioned extensively about their dietary habits and lifestyle and were examined for signs of adenomas in the rectum both at the beginning and end of the study.
The authors found that among patients who took calcium, the size and growth of the benign tumors -- as measured by pathologists who looked at tissue biopsies -- was reduced by 58%. In contrast, only a 26% reduction was seen in patients who did not take calcium.
The protective effect of calcium was most pronounced among the patients on a low-fat diet and taking calcium: 73% of those patients had noticeable reductions in adenomas. In contrast, there were no differences in adenoma reductions between high-fat eaters in the calcium and no-calcium groups.
The beneficial effects of calcium supplementation were also seen among study subjects with diets that were high in carbohydrates. High-fiber diets, however, did not appear to reduce the risk for developing cancer, a finding supported by other recent studies.
Although the study findings corroborate results from some studies of diet and cancer risk in animal studies, they are at odds with some other human studies indicating that calcium does not have a beneficial effect on the sprouting of polyps, says John A Baron, MD, a researcher who has investigated the role of calcium in prevention of colorectal cancer.
His study of calcium's effect on adenomas found a suppression of the occurrence of adenomas but no effect on size and growth, Baron tells WebMD. Trying to explain the differing results, he says that Rozen's study results may be "a chance finding" or perhaps calcium "affects adenomas in some other way." Baron is professor of medicine, professor of community and family medicine, and chief of biostatistics and epidemiology at Dartmouth Medical School in Lebanon, N.H.
Baron, who was not involved in the Israeli study, says that measuring the growth or shrinkage of adenomas over time can be a tricky business, and the results of even careful studies can be influenced by other factors.
In response, Rozen and colleagues acknowledge that calcium supplements may have a minor effect in preventing colorectal cancer but say "it would seem reasonable to give them with additional relevant dietary and lifestyle counseling" to patients at high-risk of colorectal cancer.