Physical activity and risk of breast cancer in premenopausal women

Abstract

Physical activity appears to be inversely related to risk of breast cancer, yet the results remain inconsistent. To evaluate this relation among premenopausal women and examine variation in risk according to level of obesity and use of oral contraceptives (OCs), the authors examined data from the Nurses' Health Study II. During 10 years of follow-up, 849 cases of invasive premenopausal breast cancer were confirmed. Physical activity was assessed by self-report at baseline and during follow-up using a validated questionnaire. Total physical activity was unrelated to risk of breast cancer. Women engaging in X27 metabolic equivalent (MET)-h week À1 had a multivariate-adjusted relative risk (RR) of 1.04 (95% confidence interval (CI) 0.82 -1.33) compared to those in the o3 METh week À1 category. Among women with a BMI X30 kg m À2 , we observed a significant positive dose -response relation (P ¼ 0.04). Activity was unrelated to breast cancer risk at lower levels of BMI. A test for interaction between activity and BMI (o30, X30 kg m À2 ) was statistically significant (P ¼ 0.02). Among current OC users, higher activity was associated with a non-significantly lower risk of breast cancer (RR ¼ 0.59, 95% CI 0.30 -1.16 for X27 vs o9 MET-h week À1 , P for linear trend ¼ 0.14). These results show no overall association between physical activity and risk of breast cancer among premenopausal women, but suggest that the effect of physical activity could be substantially modified by the underlying degree of adiposity. The potential interactions between physical activity, adiposity, and current use of OCs require further study. The relation of physical activity to risk of breast cancer has been assessed by the International Agency for Research on Cancer, which concluded that, although studies have not been entirely consistent, the overall results support a reduction in risk with higher levels of activity (International Agency for Research on Cancer, 2002). The majority of studies, however, have been focused on postmenopausal breast cancer. Also, upon review of more than 30 studies, it was noted that the most important time periods in life for activity is not currently known. Furthermore, which activities may offer the greatest protection have not been systematically examined.In a previous analysis of the Nurses' Health Study II (NHSII) cohort with 372 cases among predominantly premenopausal women, Rockhill et al (1998) observed no association between nonoccupational activity levels in late adolescence or the recent past and risk of breast cancer. We now extend that analysis, adding 477 additional premenopausal cases in an effort to understand better the relation between physical activity and risk of premenopausal breast cancer.In addition to evaluating the type of physical activity, we examined the relation between activity and breast cancer within subgroups of adiposity and oral contraceptive (OC) use, which we hypothesised, might modify the relationship. Potential health effects of (OCs) were the original focus of the NHS II coh...

Recent Recreational Physical Activity and Breast Cancer Risk in Postmenopausal Women in the E3N Cohort

“…HRs for hormone receptor-defined invasive breast cancer according to level of recreational physical activity within the previous 4 years Contrary to most studies, which have not found that the relation between physical activity and breast cancer risk was modified by weight changes before inclusion (9,11,13,21,30), three articles report that the risk decrease associated with baseline physical activity is restricted to postmenopausal women with limited weight gain between youth and baseline (22,31,32). However, a weight gain before baseline may be associated with a decrease in physical activity after baseline (33).…”

Body fatness and physical activity at young ages and the risk of breast cancer in premenopausal women

“…Recent reviews concluded that physical activity both at young ages and in adulthood reduced the risk of breast cancer; IARC (2002) and Lagerros et al (2004). However, subsequent findings concerning premenopausal breast cancer are inconsistent, both for physical activity at young ages (Dorn et al, 2003;Steindorf et al, 2003;Yang et al, 2003;Margolis et al, 2005) and around diagnosis (AdamsCampbell et al, 2001;Gilliland et al, 2001;Matthews et al, 2001;Colditz et al, 2003;Dorn et al, 2003;Hirose et al, 2003;John et al, 2003;Steindorf et al, 2003;Yang et al, 2003;Margolis et al, 2005). Without evidence from a formal meta-analysis using individual data from all relevant studies, it is difficult to interpret the available results.…”

“…Although an expert group convened by the International Agency for Research on Cancer concluded that there was sufficient evidence that physical activity reduced the risk of premenopausal breast cancer (IARC, 2002), results from more recent studies have been contradictory (Adams-Campbell et al, 2001;Gilliland et al, 2001;Matthews et al, 2001;Colditz et al, 2003;Dorn et al, 2003;Hirose et al, 2003;John et al, 2003;Steindorf et al, 2003;Yang et al, 2003;Margolis et al, 2005).…”

Physical Activity and Breast Cancer Risk Among Women in the Southwestern United States

“…Physical activity has been shown to reduce risk of breast cancer (1)(2)(3)(4)(5)(6). Studies have suggested that total activity, lifetime recreational activity, nonrecreational activity, and vigorous activity may be important components of activity that influence breast cancer risk (2,3,6,7).…”