Flood notes that more research needs to be done to understand why and how calcium provides protection against colorectal cancer in some women.
"We really don't know at this point," Flood said. "There are currently two main theories. One is that calcium has the ability to neutralize secondary bile acids that are produced during the digestion of fat and are highly irritating to the cells in the lining of the colon. The evidence in support of this theory is not very strong.
"An alternate theory is that calcium has a direct impact on a whole series of biochemical pathways within the cells that line the colon and rectum. These pathways play important roles in regulating how these cells grow and mature and thus, can be important components of the cancer process."
To put the study results in perspective, Flood says consuming a diet rich in calcium one that provides at least 800 mg per day, which is actually lower than the current recommended daily allowance of 1,200 mg per day--is a safe and effective way for women to help guard themselves against colorectal cancer.
As for the benefit of calcium for men, he said, "The results of this study are consistent with other studies that show calcium reduces risk of colorectal cancer in both women and men. A note of caution for men, however, is that dairy foods, the primary source of calcium in the U.S. diet, have been linked in some studies to increased risk of prostate cancer."
More about the study
The 45,354 women in this study were selected from the Breast Cancer Detection Demonstration Project (BCDDP), which was a breast cancer screening program conducted jointly by NCI and the American Cancer Society between 1973-1980.
The women initially completed a 62-item questionnaire that assessed their usual daily diet, lifestyle habits and patterns, and use of over-the-counter nonsteroidal anti-inflammatory medicines.
Contact: Mary Lawson
University of Minnesota