Body Size, Physical Activity and Risk of Breast Cancer - A Case Control Study in Jangsu Province of China

To evaluate the relationship between body size, physical activity and risk of breast cancer, we conducted acase-control study with 669 cases and 682 population-based controls in Jiangsu Province of China. A structuredquestionnaire was used to elicit detailed information. All subjects completed an in-person interview. The bodymass index (BMI) was calculated based on weights and heights. Unconditional logistic regression analysis wasperformed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) as measures of risk for breastcancer. Current height, weight and weight at around age 20 years were significantly positively correlated withrisk of breast cancer. Obese women (current BMI ≥25 kg/m2) were at significantly increased risk for developingbreast cancer (adjusted OR=1.35, 95%CI: 1.01-1.81), but, between BMI at around age 20 years and risk ofbreast cancer showed an inverse association (P for trend = 0.001). Women who had middle physical force workwere at significantly lowered OR (0.62, 95%CI: 0.41-0.93) compared with women of headwork. Using womenwho standing or ambulation per day less than one hour as the reference, women who standing or ambulationmore than one hour had a decreased risk of breast cancer. Using women who slept less than 5 hours per day asthe reference, the women who slept 5-8 hours were at significantly decreased risk of breast cancer. Women whohad habit of recreational physical activity were at significantly decreased risk (adjusted OR=0.68, 95%CI: 0.53-0.88), with an inverse association between the exercise times per week and risk of breast cancer (P for trend =0.025). These findings support that breast cancer risk is associated with body size, and that moderate occupationaland recreational physical activity has protective effects on breast cancer.