Dietary Calcium May Reduce the Risk of Colon Cancer
BOSTON--Higher calcium intake may reduce the risk of developing colon cancer, according to Kana Wu, M.D., Ph.D., and Edward Giovannucci, M.D., Sc.D., and researchers at the Harvard School of Public Health. Their study, printed in the March 20 issue of the Journal of the National Cancer Institute (94, 6:437-46, 2002) (jncicancerspectrum.oupjournals.org/jnci), consisted of more than 130,000 cases gathered from two prospective cohorts.
Researchers reviewed 87,998 female cases from the Nurses' Health Study (NHS) and 47,344 male cases from the Health Professionals Follow-up Study (HPFS) and discovered that consuming 700 mg/d to 1,250 mg/d of calcium may reduce the risk of developing distal colon cancer in both men and women. The National Academies recommend adults consume between 1,000 mg/d and 1,300 mg/d of calcium, with an upper limit set at 2,500 mg/d.
Study participants completed a food frequency questionnaire and provided information on medical history and lifestyle factors at baseline (1980 for NHS and 1986 for HPFS), and dietary information was updated at least every four years. During the follow-up period (1980 to May 31, 1996, for NHS; 1986 to January 31, 1996, for HPFS), 626 female and 399 male colon cancer cases were identified. In both sexes, higher calcium intake seemed to lead to a reduced risk of distal colon cancer. Researchers hypothesized that this was due to calcium slowing down epithelial cell growth, a process that can lead to cancer.
Participants who consumed more than 700 to 800 mg/d of dietary calcium had a 40 percent to 50 percent lower risk of developing distal colon cancer compared with those consuming less than 500 mg/d. In addition, authors stated that calcium supplementation among participants with low calcium intake appeared to decrease the risk of colon cancer. However, among participants who consumed more than 700 mg/d of dietary calcium, no added benefits were achieved by taking supplements. Authors concluded that calcium, rather than another component of dairy, may be the relevant component in reducing colon cancer risk.
Calcium's protective effect was limited to the distal colon, as calcium intake did not appear to affect the risk of cancers in the proximal (right) colon. Researchers stated that future research should be conducted to determine which specific cancer subsites are affected by calcium consumption, as well as to determine if there is a dose-response relationship.