Physical activity and breast cancer survival: results from the Nurses’ Health Studies

Abstract

Background: Physical activity is generally associated with better outcomes following diagnosis; however, few studies have evaluated change in pre- to postdiagnosis activity and repeated measures of activity by intensity and type. Methods: We evaluated physical activity and survival following a breast cancer diagnosis in the Nurses’ Health Study and Nurses’ Health Study II (n ¼ 9308 women, n ¼ 1973 deaths). Physical activity was evaluated as updated cumulative average of metabolic equivalent of task (MET)-h/wk (assigned per activity based on duration and intensity) and change in pre- to postdiagnosis activity. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results: Higher postdiagnosis activity was inversely associated with breast cancer–specific mortality in categories from ≥9 MET-h/ wk (vs <3 MET h/wk, HR≥9 to <18 ¼ 0.74 [95% CI ¼ 0.55 to 0.99]; HR≥27 ¼ 0.69 [95% CI ¼ 0.50 to 0.95]; Ptrend ¼ .04) and all-cause mortality from ≥3 MET-h/wk (HR≥3 to <9 ¼ 0.73 [95% CI ¼ 0.61 to 0.88]; HR≥27 ¼ 0.51 [95% CI ¼ 0.41 to 0.63]; Ptrend < .001). Associations were predominantly observed for estrogen receptor–positive tumors and in postmenopausal women. Walking was associated with lower risk of all-cause mortality (≥9 vs <3 MET-h/wk, HR¼ 0.69 [95% CI ¼ 0.57 to 0.84]) as was strength training. Relative to stable activity pre- to postdiagnosis (63 MET-h/wk), increases from ≥3 to 9 MET-h/wk were associated with lower all-cause mortality risk (Ptrend