“Our findings provide support for inverse associations between intakes of calcium and dairy foods and the risk of colorectal cancer,” wrote lead author Susanna Larsson from the Karolinska Institute, Stockholm.

The Cohort of Swedish Men studied 45306 men aged between 45 and 79 for seven years. Dietary intakes were quantified by use of a cross-validated food frequency questionnaire, and the results were published in the March issue of the American Journal of Clinical Nutrition (Vol. 83, pp. 667-673).

The researchers calculated that the men who consumed more than seven servings of dairy every day were 54 per cent less likely to develop colorectal cancer compared to those who ate less than two servings every day.

Interestingly, high calcium intake did not result in the same risk reduction as dairy (32 per cent risk reduction), adding to evidence from previous studies that suggest the protective effects of dairy may be due to other factors, such as conjugated linoleic acid (CLA), sphingolipids, and milk proteins.

Unlike other studies, the scientists attempted to determine if dairy intake was related to reductions of risk for specific types of colorectal cancer: cancer of the proximal colon, the distal colon, and the rectum.

James Fleet from Purdue University praised the study's design, highlighting the large sample population, the differentiation of cancer subtypes, and use of complete health records.

In an accompanying editorial in the Journal (Vol. 83, pp. 527-528), Fleet also noted the discrepancy between dairy and calcium intake and the decrease in colorectal cancer risk, and said that the study had left many questions unanswered.

“No attempts were made by the authors to estimate consumption of [other] dietary factors, nor did they discuss how milk or dairy intake provides protection in the distal colon that is not afforded by calcium alone,” said Fleet.

The disagreement with other studies about the level of calcium intake also needs to be corrected, said Fleet. Previous studies have reported optimum calcium intake to be less than 1100 milligrams per day. Larsson reported that 1400 mg per day was beneficial.

The majority of studies looking at dairy intake have reported benefits in relation to colorectal cancer. However, the recently published and much publicized Women's Health Initiative reported no link between calcium and vitamin D supplements and the disease.

Several experts spoke out against the WHI stating that the overlapping dietary intervention and hormone replacement trials had complicated the results.

It was also evident from the WHI data that the difference in vitamin D and calcium levels between intervention and control groups was not very large, and that the doses of vitamin D and calcium may have been too low to create a response.

The authors did not attempt to measure the impact of vitamin D status.

“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 and cancer risk should not ignore it,” concluded Fleet.