Abstract B143: Physical activity and risk for breast cancer in postmenopausal Chinese women
Authors: Matthews Charles , Shu Xiao-ou , Yang Gong , Li Honglan , Cai Hui , Gao Jing , Zheng Wei , Gao Yu-Tang 
Published: May 2012

Abstract
B143
Physical inactivity has emerged as a probable risk factor for post-menopausal breast cancer but our understanding of the type and amount of activity that confers benefit, and the influence of body size on activity associations, remains incomplete. In the Shanghai Women's Health Study, a prospective cohort study of 75,000 women, we examined associations between specific types, intensities, and amounts of physical activity and risk for postmenopausal breast cancer. We also described the joint-effects of activity levels and body-size on risk. Physical activity at home, work, for transportation and in leisure-time, and relevant covariates, were assessed by in-person interview. Height and body mass were measured. Proportional hazards models were used to estimate hazard ratios and 95% confidence intervals (HR [95% CI]) while adjusting for demographic characteristics and major breast cancer risk factors. This analysis includes postmenopausal women without a history of heart disease, stroke, or cancer at baseline and complete covariate data (N=48,707). Over 7.4 (SD=1.1) yrs of follow-up 467 incident breast cancers were identified. Exercise participation (last 5 yrs) assessed at study enrollment at levels that were at or above the current recommendations (7.5+ MET-hrs/wk/yr) were associated with a lower risk (HR=0.73 [0.56-0.95]), compared to no exercise. Less than 5% of women reported vigorous exercise (6+ METS) and there was no evidence for association for these participants (HR=1.12 [0.67-1.86]). Also there was no evidence of an inverse association between non-exercise activities (i.e., walking or cycling for transportation, housework, stair climbing) and breast cancer. In contrast, women that were exposed to more sedentary work environments (e.g., professional and clerical work) over their lifetime were at a 30% greater risk for breast cancer compared to women exposed to occupations requiring active manual work. Women that were least active at work and that also did not exercise at recommended levels were at nearly a two-fold greater risk for breast cancer (HR=1.89 [1.23-2.90]), compared to women that were active at work and in leisure-time. In terms of modification of the activity effects by body size, women with a body mass index (BMI) at or above the median level (23.9 kg/m2) that did not exercise at recommended levels were at higher risk (HR=1.66 [1.16-2.37]), but women in this BMI category that exercised at higher levels were not (HR=1.07 [0.68-1.68]), both compared to lean (&lt; 23.9 kg/m2) active women. Similar patterns of association were observed for occupational activity exposures and BMI levels. In conclusion, results from this prospective study support that idea that moderate intensity exercise, at or above the currently recommended levels (7.5+ MET-hrs/wk), is associated with about a 25% lower risk of postmenopausal breast cancer, and that exposure to a sedentary workplace is associated with higher risk. They also suggest that higher levels of activity may offset some of the risk associated with elevated adiposity among postmenopausal Chinese women. To minimize risk for postmenopausal breast cancer, women are encouraged to exercise at recommended levels and maintain a healthy body mass, particularly if they are or have been exposed to a sedentary work environment.
Citation Information: Cancer Prev Res 2008;1(7 Suppl):B143.