Recreational physical activity, body size, and breast cancer survival among young women

Most epidemiologic studies report a reduced risk of breast cancer incidence associated with high levels of recreational physical activity, but little is known regarding the effect on prognosis. Among post-menopausal women, obesity is linked to an increased risk of breast cancer incidence and poorer subsequent survival. For pre-menopausal women obesity may reduce the risk of developing breast cancer, but the effect on prognosis is less understood. This study investigated whether activity undertaken prior to diagnosis or obesity near diagnosis influence breast cancer survival among a population-based cohort of young women. A follow-up study was conducted among 1264 women aged 20-54 years who were diagnosed with invasive breast cancer between 1990-1992. Cases were interviewed within several months of diagnosis, and asked about their average frequency of recreational physical activity and weight at age 20 and near diagnosis. Anthropometric measures were taken during the interview. With 8-10 years of follow-up, all-cause mortality status was determined using the National Death Index (n = 290 deaths). Hazard ratios (HR) and 95% confidence intervals (CI) were estimated for the association between levels of activity or body size and all-cause mortality. A modest inverse association was observed for increased recreational activity in the year prior to diagnosis, particularly among those who were overweight or obese. This inverse association was not evident for activity at age 13 or age 20. High body mass index (BMI) or waist-hip-ratio (WHR) near diagnosis as well as history of being overweight or obese throughout early adulthood were associated with an increased risk of mortality. For increased WHR and BMI, a more pronounced HR was found for women with low levels of recreational physical activity. An elevated HR was noted for increased WHR, but not BMI, in relation to current cigarette use, high alcohol consumption, and a positive family history of breast cancer. This study provides some suggestive evidence for a beneficial effect of recreational physical activity undertaken in the year prior to diagnosis on breast cancer survival, particularly among women who are overweight or obese at diagnosis. Furthermore, breast cancer survival is reduced among young women who are generally obese (BMI) or have abdominal obesity (WHR).