Colon cancer occurs more frequently in people who are obese than in those of a healthy weight. An increased risk of colon cancer has been consistently reported for men with high BMIs. The relationship between BMI and risk in women, however, has been found to be weaker or absent.
Unlike for breast and endometrial cancer, estrogen appears to be protective for colon cancer for women overall. However, obesity and estrogen status also interact in influencing colon cancer risk. Women with a high BMI who are either premenopausal or postmenopausal and taking estrogens have an increased risk of colon cancer similar to that found for men with a high BMI. In contrast, women with a high BMI who are postmenopausal and not taking estrogens do not have an increased risk of colon cancer.
There is some evidence that abdominal obesity may be more important in colon cancer risk. In men, a high BMI tends to be associated with abdominal fat. In women, fat is more likely to be distributed in the hips, thighs, and buttocks. Thus, two measures of abdominal fat, waist-to-hip ratio or waist circumference, may be better predictors of colon cancer risk. Few studies have yet compared waist-to-hip ratios to colon cancer risk in women, however. One study that did find an increased risk of colon cancer among women with high waist-to-hip ratios found that the association was present only among inactive women, suggesting that high levels of physical activity may counteract the effects of increased abdominal fat.
A number of mechanisms have been proposed for the adverse effect of obesity on colon cancer risk. One of the major hypotheses is that high levels of insulin or insulin-related growth factors in obese people may promote tumor development.
This information is produced and provided by the National Cancer Institute (NCI). References are available at their website at www.cancer.gov. The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via www.cancer.gov or call 1-800-4-CANCER.