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 a case-control study with 669 cases and 682 population-based controls in Jiangsu Province of China. A structured questionnaire was used to elicit detailed information. All subjects completed an in-person interview. The body mass index (BMI) was calculated based on weights and heights. Unconditional logistic regression analysis was performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) as measures of risk for breast cancer. Current height, weight and weight at around age 20 years were significantly positively correlated with risk of breast cancer. Obese women (current BMI > or = 25 kg/m2) were at significantly increased risk for developing breast cancer (adjusted OR= 1.35, 95%CI: 1.01-1.81), but, between BMI at around age 20 years and risk of breast cancer showed an inverse association (P for trend = 0.001). Women who had middle physical force work were at significantly lowered OR (0.62, 95%CI: 0.41-0.93) compared with women of headwork. Using women who standing or ambulation per day less than one hour as the reference, women who standing or ambulation more than one hour had a decreased risk of breast cancer. Using women who slept less than 5 hours per day as the reference, the women who slept 5-8 hours were at significantly decreased risk of breast cancer. Women who had 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 occupational and recreational physical activity has protective effects on breast cancer.