BETHESDA, MD. — Women with higher intake of calcium appear to have a lower risk of cancer overall, and both men and women with high calcium intakes have lower risks of colorectal cancer and other cancers of the digestive system, according to a report in the Feb. 23 issue of Archives of Internal Medicine, a publication affiliated with the American Medical Association.
Yikyung Park, Sc.D., of the National Cancer Institute (N.C.I.) and colleagues analyzed data from 293,907 men and 198,903 women who participated in the National Institutes of Health-AARP Diet and Health Study. Participants took a food frequency questionnaire when they enrolled in the study between 1995 and 1996, reporting how much and how often they consumed dairy and a wide variety of other foods and whether they took supplements. Their records were then linked with state cancer registries to identify new cases of cancer through 2003.
Over an average of 7 years of follow-up, 36,965 cancer cases were identified in men and 16,605 in women. Calcium intake was not associated with total cancer in men but was in women — the risk decreased in women with intake of up to 1,300 mg per day, after which no further risk reduction was observed.
"In both men and women, dairy food and calcium intakes were inversely associated with cancers of the digestive system," the authors said.
The one-fifth of men who consumed the most calcium through food and supplements (about 1,530 mg per day) had a 16% lower risk of cancer of the digestive system than the one-fifth who consumed the least (526 mg per day).
For women, those in the top one-fifth of calcium consumption (1,881 mg per day) had a 23% lower risk than those in the bottom one-fifth (494 mg per day). The decreased risk was particularly pronounced for colorectal cancer.
Calcium and dairy food intake was not associated with prostate cancer, breast cancer or cancer in any other anatomical system besides the digestive system, according to the study.
"Dairy food, which is relatively high in potentially anticarcinogenic nutrients such as calcium, vitamin D and conjugated linoleic acid, has been postulated to protect against the development of colorectal and breast cancer," the authors said.
Calcium has been shown to reduce abnormal growth and induce normal turnover among cells in the gastrointestinal tract and breast. In addition, it binds to bile and fatty acids, potentially reducing damage to the mucous membrane in the large intestine.
The study was funded by the Intramural Research Program of the N.C.I.