The trial, carried out by a team at Stockholm's Karolinska Institutet and the Central Hospital in Vasteras, found that middle-aged women who reported having the highest intake of the nutrient in the late 80s were almost 30 per cent less likely to have developed the cancer when they were re-assessed about 15 years later.
The research also supports consumption of high-fat dairy foods. Women who said they ate at least four servings of high fat dairy foods each day had a 41 per cent lower risk of bowel cancer, also known as colorectal cancer, than those who ate less than one portion of high-fat dairy a day.
The scientists considered whole milk, full-fat cultured milk, cheese, cream, sour cream, and butter as 'high-fat dairy foods'.
The study, reported in this month's American Journal of Clinical Nutrition (vol 82, no 4, pp894-900), adds further fuel to the debate on the role of dairy products in cancer prevention. While milk-based products have been linked to increased risk of other cancers, such as breast and prostate, the consumption of milk and calcium has previously been associated with a lower risk of bowel cancer.
Much of the research has however focused on the presence of calcium as a potential mechanism for disease prevention. It is also thought to help combat the risk of colon cancer. But the Swedish team noted in their new publication that no epidemiologic studies have evaluated CLA intake in relation to bowel cancer risk.
Bowel cancer is the third most common form of the disease worldwide.
The researchers analysed data from 60,708 women aged 40-76 years old who participated in the Swedish Mammography Cohort. Their consumption of high-fat dairy foods was assessed at baseline and at the study end, on average 14.8 years later. At this point, almost 800 women had developed bowel cancer.
After adjustment for age and other potential confounders, the researchers reported that "each increment of two servings of high-fat dairy foods per day corresponded to a 13 per cent reduction in the risk of colorectal cancer".
For CLA, the multivariate rate ratio of colorectal cancer in a comparison of the two extreme quartiles of intake was 0.71.
Some studies on animals have shown CLA to be effecting in fighting and preventing certain cancers but so far there is little evidence in humans to support these findings.