Calcium supplements may help prevent the polyps that often lead to colon cancer, but a new study suggests it's still not clear whether calcium can prevent colorectal cancer itself.

Researchers reviewed two large studies on the effects of calcium supplements on colorectal cancer and found that people who took calcium had about a 25 percent lower risk of developing polyps in their colon. But they say that's not enough to recommend widespread use of calcium supplements in hopes of preventing colon cancer.

Colorectal cancer is one of the most common and deadly types of cancers in men and women. Although the exact cause is unknown, studies have suggested that various dietary factors, such as calcium, meat, fat, fiber, and vegetable consumption, may play a role in colorectal cancer risk.

Researchers say about 30 percent of older adults develop polyps in their colon. In many cases, they are noncancerous. But if left unchecked, the polyps can lead to colorectal cancer.

Read WebMD's "What Causes, Prevents Colon Polyps"

Calcium and Colorectal Cancer

In the study, which appears in the current issue of The Cochrane Library, researchers reviewed two studies on the role of calcium supplements in preventing the polyps often associated with colorectal cancer.

The studies involved more than 1,300 people who took calcium supplements and were followed for three to four years.

Researchers say the results suggest that taking 1,200 milligrams of calcium per day seems to have a moderately protective effect in reducing the risk of polyps.

Although taking calcium supplements is generally safe, researchers say more studies are needed before they can recommend calcium supplementation for the prevention of colorectal cancer.

Researchers say people need about 1,750 milligrams of calcium a day; calcium supplements usually range from 500 milligrams to 1,500 milligrams. They caution that taking higher doses of calcium may not be well tolerated by some people.

But if further studies confirm these protective effects, calcium supplements may be recommended for people who had polyps before and are at higher risk for developing colorectal cancer.

Read WebMD's "41 Million People Need Colon Cancer Screening"

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Weingarten, M. The Cochrane Database of Systemic Reviews, July 20, 2005. News release, Health Behavior News Service.