Intentional weight loss and incidence of obesity-related cancers: the Iowa Women's Health Study

OBJECTIVE: To examine the association of voluntary vs involuntary weight loss with incidence of cancer in older women. DESIGN: Prospective cohort study from 1993 to 2000, with cancer incidence identified through record linkage to a cancer registry. SUBJECTS: A total of 21 707 postmenopausal women initially free of cancer. MEASUREMENTS: Women completed a questionnaire about intentional and unintentional weight loss episodes of greater than or equal to20 pounds during adulthood. RESULTS: Compared with women who never had any greater than or equal to20 pounds weight loss episode, women who ever experienced intentional weight loss greater than or equal to20 pounds but no unintentional weight loss had incidence rates lower by 11% for any cancer (RR = 0.89, 95% CI 0.79-1.00), by 19% for breast cancer (RR = 0.81, 95% CI 0.66-1.00), by 9% for colon cancer (RR = 0.91, 95% CI 0.66-1.24), by 4% for endometrial cancer (RR = 0.96, 95% CI 0.61-1.52), and by 14% for all obesity-related cancer (RR = 0.86, 95% CI 0.74-1.01) after adjusting for age, body mass index, waist-to-hip ratio, physical activity, education, marital status, smoking status, pack-years of cigarettes, current estrogen use, alcohol use, parity, and multivitamin use. Furthermore, although overweight women were at increased risk of several cancers, women who experienced intentional weight loss episodes of 20 or more pounds and were not currently overweight were observed to have an incidence of cancer similar to nonoverweight women who never lost weight. Unintentional weight loss episodes were not associated with decreased cancer risk. CONCLUSIONS: These findings suggest that intentional weight loss might reduce risk of obesity-related cancers.