LAUSR

OBJECTIVE To assess the associations among several anthropometric measures, as well as BMI trajectories and CRC risk in older women. DESIGN Prospective cohort study. SETTING Forty clinical centres in the USA. PARTICIPANTS 79,034 postmenopausal women in the Women's Health Initiative Observational Study. RESULTS During an average of 15.8 years of follow-up, 1,514 CRC cases were ascertained. Five BMI trajectories over 18 to 50 years of age were identified using growth mixture model. Compared with women who had a normal BMI at age 18, women with obesity at age 18 had a higher risk of CRC (HR 1.58, 95%CI 1.02-2.44). Compared with women who kept relatively low normal body size during adulthood, women who progressed from normal to obesity (HR 1.29, 95%CI 1.09-1.53) and women who progressed from overweight to obesity (HR 1.37, 95%CI 1.13-1.68) had higher CRC risks. A weight gain > 15 kg from age 18 to 50 (HR 1.20, 95%CI 1.04-1.40) and baseline waist circumference >88 cm (HR 1.33, 95%CI 1.19-1.49) were associated with higher CRC risks, compared to stable weight and waist circumference ≤88cm respectively. CONCLUSION Women who have a normal weight in early adult life and gain substantial weight later, as well as those who are persistently heavy over adulthood, demonstrated a higher risk of developing CRC. Our study highlights the importance of maintaining a healthy body weight over the life course for reducing the risk of developing CRC in women.