Older adults who are heavy, especially around the middle, seem to have a higher risk of developing colon cancer than their thinner peers -- and exercise may lower the incidence of the disease, especially for women, a European study said.
More than 120,000 adults in the Netherlands aged 55 to 69 were followed for 16 years by the study, published in the American Journal of Epidemiology.
During that time, about two percent developed colorectal cancer, tumors of the colon and/or rectum, though most were diagnosed with colon cancer.
The risk was 25 percent higher for men who were significantly overweight or obese at the outset, versus normal-weight men.
"The study provides further evidence that excess body fat may contribute to a higher risk of colorectal cancer," said lead researcher Laura Hughes, at Maastricht University in the Netherlands, in an e-mail.
For men, 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.
Among women, though, a large waistline was only linked to a higher cancer risk in women who also got little exercise, defined as less than 30 minutes a day.
Women who topped a "44" in pants size -- about a size 16 in the United States -- 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 a day.
Studies have tied abdominal obesity to other health conditions, such as diabetes and heart disease, and belly fat seems to be particularly linked to chronic, low-level inflammation in the body, Hughes added.
"One of our most intriguing observations was that abdominal fat was associated with colorectal cancer in women only when combined with low exercise levels," she said.
It's not clear why that might be, or why the pattern was seen only in women, Hughes added. Calorie balance, or how much you take in through food versus how much you burn through exercise, may be important.
"Women should focus on maintaining a healthy lifestyle rather than simply paying attention to what the scale says," Hughes added.
Risk factors for colorectal disease include older age, a history of colitis or Crohn's disease, a family history of the cancer, and smoking. Some studies have also linked diets high in animal fat, and low in fruits, vegetables and fibre to an increased risk.