Adults who carry much of their fat around the middle may be at increased risk of colon cancer, a large European study suggests.

Researchers found that among nearly 370,000 adults from nine European countries, men and women with large waistlines were more likely to develop colon cancer than those who were trimmer around the middle.

Waist size and waist-to-hip ratio, which are both indicators of abdominal obesity, appeared more important in colon cancer risk than does overall weight. In fact, the study found that body mass index (BMI) - a measure of weight in relation to height - was unrelated to colon cancer risk among the women.

The findings, reported in Wednesday’s issue of the Journal of the National Cancer Institute, suggest that abdominal fat holds a particular influence over colon cancer risk.

People with large waistlines often have a high amount of fat around the abdominal organs, and this type of fat is more “metabolically active,” explained Dr. Tobias Pischon, a researcher at the German Institute of Human Nutrition in Potsdam-Rehbruecke and the lead author of the study.

It’s possible, he told Reuters Health, that this visceral fat increases colon cancer risk by raising levels of certain hormones that affect cell growth, including the growth of cancer cells. For example, the researcher noted, people with type 2 diabetes have a higher rate of colon cancer - supporting a potential role for the hormones insulin and insulin-like growth factor 1 in promoting tumor cell growth.

Whatever the reason, the new findings point to the importance of preventing abdominal obesity in particular, according to Pischon.

The findings come from a large ongoing study of nutrition and cancer risk among European adults. The researchers included 368,277 men and women who had their weight and body measurements taken and who completed questionnaires on diet, exercise and other lifestyle factors at the start of the study.

Over the next six years, the researchers found that adults with larger midlines were more likely to develop colon cancer. Compared with the slimmest men, those with the largest waistlines were 39 percent more likely to be diagnosed with the cancer; women with the most fat around the middle had a 48-percent higher risk of the disease than those with the smallest waistlines.

BMI was linked to colon cancer risk among men only.

Previous studies have found the same sex difference when it comes to BMI and colon cancer risk, according to Pischon’s team. One reason, they note, may be the differences in body fat distribution between men and women.

When a man has a high BMI, it’s typically because of fat around the middle. Women, on the other hand, often carry much of their fat around the hips and thighs.

So waist size may be a more accurate predictor of colon cancer risk than overall BMI, particularly for women, according to Pischon.

“Our study shows that it’s more important to keep an eye on the waist circumference, especially in women,” he said.

SOURCE: Journal of the National Cancer Institute, July 5, 2006.