Intake of dairy foods and calcium is inversely related to risk for colon cancer, according to the results of a large, prospective cohort study reported in the March issue of the American Journal of Clinical Nutrition.

"Recent epidemiologic studies have generally reported a modest inverse association between calcium intake and the risk of colorectal cancer," write Susanna C. Larsson, MD, from Karolinska Institutet in Stockholm, Sweden, and colleagues. "However, findings pertaining to specific subsites in the colorectum have been conflicting."

In the Cohort of Swedish Men, 45 306 men aged 45 to 79 years and without a history of cancer completed a food-frequency questionnaire in 1997 and were followed up through December 31, 2004.

During a mean follow-up of 6.7 years, 449 incident cases of colorectal cancer occurred. After adjustment for age and other risk factors, the multivariate rate ratio (RR) of colorectal cancer for men in the highest quartile of total calcium intake compared with those in the lowest quartile was 0.68 (95% confidence interval [CI], 0.51 - 0.91; P for trend = .01).

High dairy consumption was also associated with a lower risk for colorectal cancer. Colorectal cancer risk for 7 servings/day or more of total dairy foods was about half that for less than 2 servings/day (multivariate RR, 0.46; 85% CI, 0.30 - 0.71; P for trend = .01). Milk was the dairy food that was most strongly inversely associated with the risk for colorectal cancer.

For cancer subsites, RRs were 0.37 for proximal colon (95% CI, 0.16 - 0.88), 0.43 for distal colon (95% CI, 0.20 - 0.93), and 0.48 for rectum (95% CI, 0.23 - 0.99).

"Our findings provide support for inverse associations between intakes of calcium and dairy foods and the risk of colorectal cancer," the authors write. "The associations did not vary significantly by subsite in the colorectum."

Study limitations include possible misclassification of calcium intake, and the possibility of unmeasured confounders accounting for the observed associations.

"Future studies should examine the relation of other components of dairy foods, such as conjugated linoleic acid, sphingolipids, and milk proteins, with the risk of colorectal cancer," the authors conclude.

The Swedish Cancer Foundation, the Swedish Research Council-Longitudinal Studies, the Swedish Foundation for International Cooperation in Research and Higher Education (STINT), Västmanland County Research Fund against Cancer, Örebro County Council Research Committee, and Örebro Medical Center Research Foundation supported this study. The authors have disclosed no relevant financial relationships.

In an accompanying editorial, James C. Fleet, from Purdue University in West Lafayette, Indiana, calls this a powerful study with a large population linked to well-maintained, complete health records.

"Although this study offers some new insight into the dietary modulation of colon cancer, one is still likely to feel that this story has a lot more to reveal and that [this article] only begins to address these gaps," Dr Fleet writes. "Given that the interaction between vitamin D status and calcium metabolism is well established and that vitamin D status appears to modulate the effect of calcium on colon cancer risk, future studies on calcium or dairy intakes and cancer risk should not ignore it."