Calcium consumption can significantly lower a woman's risk of colorectal cancer, according to a recent study by Fred Hutchinson's Dr. Ulrike "Riki" Peters, of the Public Health Sciences Division.
Women who consume more than 800 milligrams of calcium each day — the equivalent of three cups of skim milk — reduce their risk of colorectal cancer by as much as 26 percent compared to women who consume about 400 milligrams of calcium each day, Peters said. This reduction in risk occurred regardless of whether the calcium intake was from diet or supplements. Among women who consumed high levels of calcium from both diet and supplements, the risk reduction was almost double that observed from either source alone.
Peters conducted the research while she was a postdoctoral fellow at the National Cancer Institute (NCI); she joined the Fred Hutchinson faculty in 2004. Dr. Andrew Flood, an epidemiologist with the University of Minnesota Cancer Center and School of Public Health, led the study, which was published in the January edition of Cancer Epidemiology Biomarkers and Prevention.
"The findings are important because colorectal cancer is such a common disease, and we all consume calcium in greater and smaller amounts," Peters said. "This study is additional evidence, a piece of the puzzle."
Growing evidence of link
The study results add to a growing body of research that indicates a link between calcium and prevention of colorectal cancer. Women comprise about half of the approximately 150,000 people in the United States diagnosed annually with colorectal cancer. Other studies point to the same protective effect in men. Colorectal cancer ranks as the third leading cause of cancer death in both men and women, and the risk increases with age.
The 10-year project began in 1987 and involved more than 45,000 women in the United States with no history of colorectal cancer. The study participants were selected from the Breast Cancer Detection Demonstration Project (BCDDP), a screening program conducted by NCI and the American Cancer Society. The women, whose average age was 61 at the start of the study, were categorized into groups by self-reported information about their diets, lifestyles and calcium-supplement intake. During the study, 482 of the women developed colorectal cancer.
Women in the lowest group consumed about 400 milligrams of calcium from diet each day. Compared to this group, women in higher-consumption groups showed reduced risk of developing colorectal cancer over the course of the study. Women in the highest group of dietary calcium intake — more than 800 milligrams daily — had a 26 percent lower risk of developing colorectal cancer.
Dietary vs supplement source
The women were also divided into groups based on their intake of calcium from supplements. Women who reported taking 800 milligrams each day of calcium from supplements had a 24 percent lower risk of developing colorectal cancer than women who took no supplemental calcium.
Getting plenty of calcium from both diet and supplements appeared to offer the greatest protective effect. The researchers found that high intake of both dietary and supplemental calcium reduced risk even more than calcium from either source alone. Women who consumed more than 400 milligrams of calcium from diet and more than 800 milligrams from supplements each day had a 46 percent lower risk of colorectal cancer than women who consumed less. The recommended daily allowance is between 1,000 to 1,200 milligrams of calcium.
"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 itself, and not the dairy products or some other variable, that accounted for the reduction in risk."
Flood said more research is needed to understand why and how calcium provides protection against colorectal cancer in some women. "There are currently two main theories," he said. "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."
"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."
This direct impact of calcium on biochemical pathways within cells is possibly mediated through the calcium-sensing receptor, to which calcium binds before signaling the cell to perform certain metabolic activities, Peters said. She and her colleagues are currently investigating if genetic markers in the calcium-sensing receptor are associated with colorectal-cancer risk. She is also studying the interaction between vitamin D and calcium at the molecular level.
Co-authors included NCI's Drs. Nilanjan Chatterjee, James Lacy, Jr., Catherine Schairer and Arthur Schatzkin. The study was funded by NCI.
Want to increase the calcium in your diet? Calcium is often found in dairy products, but there are other sources, too. Here are some calcium-rich food servings with approximate calcium content.