New York: Older adults who are heavy, especially around the middle, seem to have a higher risk of developing colon cancer than their thinner peers, a new study finds.
The findings, reported in the American Journal of Epidemiology, add to evidence that obesity is a risk factor for colon cancer.
They also suggest that exercise could be an important part of the picture, particularly for women.
The study included more than 120,000 Dutch adults ages 55 to 69 who were followed for 16 years. During that time, about two percent developed colorectal cancer (tumors of the colon and/or rectum); most were diagnosed with colon cancer.
The risk, researchers found, was 25 percent higher for men who were significantly overweight or obese at the outset, versus normal-weight men.
And waist size seemed to matter most: Men with the biggest bellies -- gauged by their self-reported "trouser size" -- had a 63 percent greater risk of colorectal cancer than men who were trimmest around the middle.
The findings were more complex among women, though. A large waistline was only linked to a higher cancer risk in women who also got little exercise (less than 30 minutes per day).
Women who topped a "44" in pants size and got little exercise were 83 percent more likely to develop colon cancer than women who had smaller waistlines and exercised more than 90 minutes per day. (A "44" in Europe translates to about a size 16 in the U.S.)
The study "provides further evidence that excess body fat may contribute to a higher risk of colorectal cancer," lead researcher Laura A.E. Hughes, of Maastricht University in the Netherlands, told Reuters Health in an email.
"It is important to maintain a healthy body weight throughout life, as this may lower your risk of colorectal cancer," she said.
It also makes sense that excessive abdominal fat would be particularly linked to the disease, according to Hughes.
Studies have tied abdominal obesity to other health conditions, like diabetes and heart disease. And belly fat seems to be particularly linked to chronic, low-level inflammation in the body, Hughes explained.
That inflammation is thought to be involved in a number of disease processes.
"One of our most intriguing observations," Hughes said, "was that abdominal fat was associated with colorectal cancer in women only when combined with low exercise levels."
It`s not clear why that might be, or why the pattern was seen only in women, she said. But the finding hints that calorie balance -- how much you take in through food, and how much you burn through exercise -- may be important, according to Hughes.
So, she said, "women should focus on maintaining a healthy lifestyle rather than simply paying attention to what the scale says."
In the U.S., it`s estimated that just over 141,000 people will be diagnosed with colorectal cancer in 2011, while nearly 50,000 will die from the disease, according to the ACS. The average American has about a 1 in 20 lifetime chance of developing the tumors.
Risk factors for colorectal cancer include older age (it`s usually diagnosed after age 50), a history of colitis or Crohn`s disease (inflammatory disorders of the colon), a family history of the cancer, and smoking.
Some studies have also linked diets high in animal fat, and low in fruits, vegetables and fiber, to an increased risk.