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By Karen Collins, R.D.

Special to MSNBC

December 10, 2004

For some time, nutrition researchers have thought that sufficient amounts of calcium in the diet may protect people from colon cancer. The results of studies vary, however. Two new explanations for this inconsistency have been offered: First, the source of calcium may make a difference. Second, inherited differences in the “receptors” on cells that process nutrients could safeguard some people more than others.

There are still good theoretical reasons linking calcium consumption to a reduced risk of colon cancer, however. These reasons tend to be supported by both laboratory and human studies.

One of the most recent analyses pooled data from ten different studies in five countries. People who consumed the most calcium had a 20 percent lower risk of colorectal cancer than those people who consumed the least calcium.

In another study, women who met or nearly met current adult calcium recommendations reduced their risk of colorectal cancer almost 30 percent compared to those who ate half the recommended amount. In this study, total calcium consumption was more significant than dairy product consumption, and vitamin D was not linked to risk.

In addition to these studies, others have shown from 15 to 30 percent drops in colorectal cancer risk for people with high calcium consumption.

Supplements vs. sources from food
Although an association between calcium intake and colon cancer risk is not seen in all studies, many scientists still think such a link exists. Calcium consumption varies widely, so studies showing no cancer risk reduction among those with the highest calcium consumption must be examined closely. Sometimes, study participants with the highest calcium intake actually consume significantly less than the recommended amounts.

For consumers, the message from the research is ambiguous. Studies have shown that a lower colon cancer risk can come from calcium supplements as well as milk. But the amount of vitamin D needed from the diet at the same time is unclear. Milk or calcium supplements that contain vitamin D would provide both nutrients. But people who get their calcium mostly from cheese, yogurt or supplements without vitamin D might be missing enough of this vitamin.

Calcium may also affect the risk for other cancers. The large Nurses’ Health Study showed that premenopausal women with the highest calcium consumption faced a 20 percent less risk of breast cancer than those with the lowest consumption. The greatest consumers of low-fat dairy foods had a 30 percent lower risk than those eating the fewest.

This last finding could reflect the benefits of other components in milk like vitamin D. Although the Nurses’ Health study showed no benefit for postmenopausal women from calcium or dairy products, another study of postmenopausal women did.

The lack of an association in the Nurses’ Health study could stem from the rather low dairy intake even among the postmenopausal women who ate the most dairy products. However, another review of studies found no link between calcium and breast cancer risk, so the possible link may be small.

In regard to whether calcium can increase the risk of prostate cancer, the risk only seems to rise if a man’s calcium consumption exceeds 2,000 milligrams daily. An excessive use of supplements is generally needed to reach this level, the equivalent of more than one-and-a-half quarts of milk.

To get enough calcium for your bones and possibly lower your risk of colon cancer, most adult men and women need only 1,000 mg of calcium a day. This recommended amount increases to 1,200 mg after age 50. You can reach either of these amounts with three servings of calcium-rich foods a day.

Nutrition Notes is provided by the American Institute for Cancer Research  in Washington, D.C.© 2004 

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