PHYSICAL-ACTIVITY AND RISK OF BREAST-CANCER IN THE FRAMINGHAM HEART-STUDY

The authors analyzed data from the Framingham Heart Study to evaluate the association between physical activity and breast cancer risk. Phys ical activity was ascertained by a physician-administered questionnair e from 2,321 women at the fourth biennial examination conducted in 195 4-1956. Breast cancers were identified by self-report, surveillance of admissions to Framingham Union Hospital, and review of death records; all but one were histologically confirmed. During 28 years of follow- up, 117 breast cancer cases were diagnosed among the 2,307 women with data on physical activity and reproductive history (a potential confou nder). Analysis was performed using Cox proportional hazards models wi th age as the underlying time variable. Models were adjusted for age a t physical activity assessment, menopausal status, age at first pregna ncy, parity, education, occupation, and alcohol ingestion. We observed a gradient of increasing risk of breast cancer with increasing physic al activity (trend p = 0.06). The relative risk for women in the highe st versus lowest activity quartile was 1.6 (95% confidence interval 0. 9-3.0; p = 0.13). Although both moderate-to-heavy leisure and occupati onal activities were associated with an increased risk, the associatio n was marginally significant only for leisure activity (p = 0.06). Our findings do not support a protective effect of physical activity duri ng adulthood for breast cancer, but suggest an increased risk among mo re active women.