The Two Nutrients Act Together to Prevent Colorectal Polyps
By Salynn Boyles
WebMD Medical News
Reviewed By Brunilda Nazario, MD
Studies show that dietary calcium helps protect against colorectal cancer, but it appears to need a little help from vitamin D. The new research shows that calcium and vitamin D act synergistically to protect against cancer of the colon. Calcium supplementation did not have much of an effect on the development of precancerous polyps when serum vitamin D levels were low in a study that involved nearly 800 people. And higher vitamin D levels were associated with a reduced risk of colorectal polyps only in people taking calcium.
“These findings suggest that from a protection standpoint, calcium and vitamin D do act together,” study co-author John A. Baron, MD, tells WebMD. “Taking calcium alone doesn’t appear to do the trick.”
Baron and colleagues had previously reported that calcium supplementation significantly reduced the risk of developing recurrent colorectal polyps in the largest placebo-controlled clinical trial of calcium and colorectal cancer prevention ever. Colorectal cancer is one of the main causes of cancer deaths in the U.S., and studies show that diets consumed by western populations have a role in causing this cancer. Calcium appears to have a role in the growth of normal colon cells. Most colorectal cancers develop from benign growths called polyps, known as adenomas, which later may develop into cancer.
In their latest report, the researchers assessed the impact of vitamin D levels on adenoma recurrence among 803 of the study participants. They found that calcium supplementation protected against new adenomas only in people with serum vitamin D levels above average levels — in this study that was a level of 29.1ng/ml. Similarly, vitamin D levels were associated with a reduced risk for polyp recurrence only among people who were taking supplemental calcium.
The reduction in colorectal cancer risk in people who took calcium and had higher levels of vitamin D was similar to that seen in those who exercise regularly, Baron tells WebMD. The study is reported in the Dec. 3 issue of the Journal of the National Cancer Institute.
What Should You Do?
While the findings show that taking calcium and getting more vitamin D can lower colorectal cancer risk, Baron says the message for the public is not so clear-cut. Several studies show a link between dietary calcium and an increased risk of prostate cancer, although the association was not seen in this study. And while exposure to the sun is one of the best ways to get vitamin D, this obviously carries its own risks.
“Right now it is difficult to know what to tell the public about these findings because there are so many variables involved,” researcher Elizabeth T. Jacobs, PhD, tells WebMD. “I know people get sick of hearing this, but we need more studies before we can make specific recommendations.”
In addition to determining the levels of dietary calcium and vitamin D needed to protect against colorectal cancer, Jacobs says future studies should also examine the impact of genetic influences linked to the cancer.
In an editorial accompanying the study, Jacobs and colleagues note that until these questions are answered, people may benefit most from adopting lifestyle changes known to reduce the risk of colorectal cancer, such as increasing physical activity, eating more fruits and vegetables, and eating less red meat.
SOURCES: John A. Baron, MD, professor of medicine, Dartmouth Medical School, Lebanon, N.H. Elizabeth T. Jacobs, PhD, assistant professor of epidemiology and biostatistics, Arizona Cancer Center, University of Arizona at Tucson. Baron, J. Journal of the National Cancer Institute, Dec. 3, 2003; vol 95: pp 1765-1771.
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