Many studies have found a positive relation between obesity and colon cancer in men but a weaker association in women (8, 22-24, 99-106). More recent data from the Nurses' Health Study suggest that the relationship between obesity and colon cancer in women may be similar to that seen in men. Twice as many women with a BMI of > 29 kg/m2 had distal colon cancer as women with a BMI < 21 kg/m2 (107). In men, the relationship between obesity and total colon cancer was weaker than that for distal colon cancer.
Other data from the Nurses' Health Study show a substantially stronger relationship between waist-to-hip ratio and the prevalence of colon polyps on sigmoidoscopy, than with BMI alone (108). Even among leaner women, a high waist-to-hip ratio is also associated with significantly increased risk of colon polyps (107).
Epidemiologic studies consistently show that obesity is directly related to mortality from breast cancer, predominantly in postmenopausal women (8), but inversely related to the incidence of premenopausal breast cancer (109-112).Ten or more years after menopause, the premenopausal "benefit" of obesity has dissipated (113). Among postmenopausal women, peripheral fat is the primary source of estrogens, the major modifiable risk factor for postmenopausal breast cancer.
This crossover in the relationship of obesity with breast cancer, pre- and postmenopausally, complicates prevention messages for this common female cancer. Recent data from the Nurses'Health Study, however, show that adult weight gain is positively related to risk of postmenopausal breast cancer. This relation is seen most clearly among women who do not use postmenopausal hormones. A gain of more than 20 lb from age 18 to midlife doubles a woman's risk of breast cancer. Even modest weight gains are positively related to risk of postmenopausal cancer (114).
Obesity increases the risk of endometrial cancer. The risk is three times higher among obese women (BMI 30 kg/m2) than among normal-weight women (115). However, the absolute risk of this condition is low when compared to breast cancer, heart disease, and diabetes. Adult weight gain is also related to increased risk (115).
Obesity is related to the risk of gallbladder cancer, particularly among women (177). Using a weight index of 100 as the average weight with a corresponding mortality ratio of 1.0 for the cohort, mortality ratios were 1.16 at a weight index of 120 to 129, 1.22 at 130 to 139, and 1.53 at 140.