"Laboratory, clinical and epidemiologic evidence suggests that calcium may help prevent colorectal adenomas," write researchers from the Calcium Polyp Prevention Study Group in a paper recently published in the New England Journal of Medicine (Vol. 340, No. 2). Adenomas, or adenomatous polyps, are growths that develop in the lining of the colon and may become cancerous.

The research team evaluated the effect of calcium supplementation on 930 people who had a history of developing colorectal adenomas. Study subjects were randomly assigned to take either calcium carbonate supplements (3 grams = 1,200 milligrams of elemental calcium) or placebo. Colonoscopies were performed one year and four years after supplementation, to detect any new polyps.

"The subjects in the calcium group had a lower risk of recurrent adenomas," the authors write. The researchers conclude that, "Calcium supplementation is associated with a significant ? though moderate ? reduction in the risk of recurrent colorectal adenomas."

Found in dairy products, leafy green vegetables

Calcium is a mineral that is found naturally in many dairy products, leafy green vegetables and some fish. Because humans cannot manufacture calcium, it must be obtained from food sources or supplements. Other research has shown it may lower risk of colorectal cancer.

A group of researchers from Columbia University has conducted a number of studies evaluating the effect of calcium on a number of diseases, including colorectal cancer. This team also looked at the effect of daily calcium intake on people with histories of colon adenomas. The researchers reported in the Journal of the American Medical Association (Vol. 280, No. 12) that, in this group of patients, increasing the daily intake of calcium up to 1,200 milligrams with low-fat dairy foods reduced the altered growth and differentiation of cells lining the colon that is believed to be a first step toward colon cancer.

Another researcher reviewed several dozen studies of the effects of calcium on various diseases and concluded that long-term deficiencies in calcium and vitamin D may lead not only to bone fragility, but also to colorectal cancer and high blood pressure in some people. Higher calcium intake may help to prevent these conditions.

Appears to detoxify cancer-causing compounds

Calcium appears to detoxify irritants and cancer-promoting compounds that often accompany a high-fat diet, which is linked to a higher risk for colon cancer. A study conducted at Texas Tech University in Lubbock concluded that, regardless of the source, adequate calcium intake as part of a healthy diet might help to prevent the formation of colorectal cancer.

"Studies in animals show that, during digestion, calcium becomes attached to molecules of fat," writes Bernard Levin, MD, in his book "Colorectal Cancer." "This prevents them from being absorbed into the body, thereby reducing the risk that the fat will trigger the abnormal cell growth of cancer. Research also indicates that calcium prevents bile salts, bile acids and certain enzymes from causing damage to cells ? specifically the cells inside the crypts of the large intestine, where potentially cancerous polyps form.

"To make use of calcium, the body must maintain adequate supplies of vitamin D. This vitamin helps the intestine to absorb calcium and allows the mineral to pass through the cell walls. Vitamin D comes from such foods as fortified milk, eggs and seafood. The body manufactures the vitamin when the skin is exposed to sunlight."

Benefits of calcium for cancer patients

Because calcium plays a crucial role in building and maintaining bone mass and strength, it can also benefit people who have cancer by reducing the risk of osteopenia (reduced bone mass) and osteoporosis (bone fragility and a severe decrease of bone mass and strength). Both conditions result from calcium deficiency and both are associated primarily with aging, although osteoporosis is a common problem for postmenopausal women. Osteopenia and osteoporosis can also result from poor nutrition, prolonged drug therapy, disease and decreased mobility, all of which may apply to people with cancer.

Some chemotherapy medications can reduce appetite, create swallowing difficulties, or cause nausea and vomiting, and result in osteopenia. The chemotherapy drugs methotrexate and doxorubicin may directly damage bones. Radiation therapy can cause osteopenia within the area being treated, and the combination of both radiation and chemotherapy can cause even greater damage to bone structure. Some cancers also can harm bones.

"?We do not yet know what dosage of calcium will offer the greatest amount of protection with the lowest risk of adverse effects," Dr. Levin writes. "Nutrition experts recommend that adolescents should consume about 1,200 mg per day and that older adults need 800 mg per day."

Dr. Levin warns that too much calcium can cause serious health problems, including kidney stones. He urges people to consult with a physician or nutritionist before increasing calcium in one?s diet.