Calcium may protect women from cancer

01/27/05

U of MN research shows calcium can help prevent colorectal cancer

A University of Minnesota Cancer Center study found that women consuming more than 800 milligrams of calcium each day reduced their risk of colorectal cancer by as much as 26 to 46 percent. A 26 percent reduction in risk of colorectal cancer occurred regardless of whether the calcium intake was from diet or supplement. Among women who consumed high levels of calcium from both diet and supplements, the risk reduction was almost double that observed for calcium from either source by itself.

The results of the study appear in this month's Cancer Epidemiology, Biomarkers and Prevention journal. Andrew Flood, Ph.D., epidemiologist with the University of Minnesota Cancer Center and School of Public Health, led the study in collaboration with the National Cancer Institute (NCI).

The study involved 45,354 women in the United States who did not have a history of colorectal cancer. The women were categorized into groups according to information they provided about their diets and lifestyles. The women averaged 61.9 years of age upon entering the study and they were followed in the study for an average of 8.5 years. This study began in 1987 and closed in 1997. During that time, 482 women in the study developed colorectal cancer.

"It is especially notable that the risk reduction was present regardless of the source of the calcium, and that simultaneously consuming high levels of calcium from both diet and supplements further reduced risk," Flood said. "These observations suggest that it was the calcium per se, and not merely dairy products or some other variable that accounted for the reduction in risk."

The findings provide further evidence in a growing body of research that indicates a link between calcium and prevention of colorectal cancer. This study is good news for women because they comprise about half of the approximately 150,000 people in the United States diagnosed annually with colorectal cancer. The cancer ranks as the second leading cause of cancer death, and the risk of contracting it increases with age.

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. A separate series of questions asked about their intake of calcium from supplements, whether multivitamins or calcium-specific.

The information received was used to categorize the women into five equally sized groups. The groups were ranked in order of increasing calcium intake, based on the dietary practices the women reported at the start of the study.

  • Women in the lowest group consumed less than 412.3 mg of calcium from diet each day.
  • Compared to the low-consuming group, women in the four higher groups (412.4-528.9 mg/d; 529.0-656.2 mg/d; 656.3-830.9 mg/d; and greater than 830.9 mg/d) all showed reduced risk of developing colorectal cancer over the course of the study.
  • Women in the highest group of dietary calcium intake greater than 830 mg/d had a 26 percent lower risk of developing colorectal cancer compared to women in the lowest group.

The women also were divided into groups based on their intake of calcium from supplements. Women who reported consuming 800 mg/d of calcium from supplements had a 24 percent lower risk of developing colorectal cancer than women who took no calcium from supplements. The researchers further found that high intake of calcium from both diet and supplements reduced risk even more than calcium from either source alone. Women who consumed more than 412.4 mg/d of calcium from diet and also consumed more than 800 mg/d from supplements had a 46 percent lower risk of colorectal cancer than women who consumed less than 412 mg/d from diet and less than 800 mg/d from supplements.

This study was funded by NCI. In addition to Andrew Flood, researchers on the study were Ulrike Peters, Fred Hutchinson Cancer Center, Seattle; and Nilanjan Chatterjee, James Lacy, Jr., Catherine Schairer and Arthur Schatzkin, all with NCI in Bethesda, MD

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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