Increased calcium intake may reduce the risk of cancers in the left, or distal, colon, report Kana Wu, M.D., Ph.D., and Edward L. Giovannucci, M.D., Sc.D., of the Harvard School of Public Health, and their coworkers. Their findings appear in the March 20 issue of the Journal of the National Cancer Institute.
Among people with low-calcium diets, even a modest increase in calcium intake appeared to offer some protection against colon cancer, the authors conclude. They caution, however, that there may be a ceiling to the beneficial effects of calcium. In their study, taking more than 700 mg of calcium per day was not associated with any further protection against colon cancer.
Researchers believe that calcium reduces the risk of colon cancer by slowing down epithelial cell growth, a process that can lead to cancer. Past studies have looked at the association between increased calcium intake and the risk of colon cancer; however, the results have been mixed.
In 1996, Wu and her coworkers reported that increased calcium intake among two large cohorts appeared to modestly reduce their risk of colorectal and colon cancer, but the results were not statistically significant.
The new study involves an extended follow-up of the same two cohorts. Wu and her coworkers analyzed calcium intake from both dairy sources and calcium supplements by roughly 88,000 women in the Nurses’ Health Study and about 47,000 men in the Health Professionals Follow-Up Study. The authors identified 626 women and 399 men with colon cancer.
Men and women who included more than 700 to 800 mg of calcium in their diets each day had a 40% to 50% lower risk of distal colon cancer compared with participants taking less than 500 mg of calcium each day. The authors note, however, that the protective effects of calcium appeared to be limited to the distal colon. Calcium intake did not seem to be associated with the risk of cancers in the right, or proximal, colon.
Calcium supplementation among those with low calcium intake did appear to decrease their risk of colon cancer. However, among participants who already consumed more than 700 mg of calcium per day, calcium supplements did not appear to be associated with further reduction in their colon cancer risk. Therefore, the authors conclude that calcium, rather than other components of dairy products, may be the relevant component in reducing colon cancer risk.
Wu K, Willett WC, Fuchs CS, Colditz GA, Giovannucci EL. Calcium intake and the risk of colon cancer in women and men. J Natl Cancer Inst 2002;94:437–46.
Source: Journal of the National Cancer Institute.