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

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 = 9308 women, n = 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) = 0.74 [95% CI = 0.55 to 0.99]; HR(≥27) = 0.69 [95% CI = 0.50 to 0.95]; P(trend) = .04) and all-cause mortality from ≥3 MET-h/wk (HR(≥3 to <9) = 0.73 [95% CI = 0.61 to 0.88]; HR(≥27) = 0.51 [95% CI = 0.41 to 0.63]; P(trend) < .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, HR= 0.69 [95% CI = 0.57 to 0.84]) as was strength training. Relative to stable activity pre- to postdiagnosis (±3 MET-h/wk), increases from ≥3 to 9 MET-h/wk were associated with lower all-cause mortality risk (P(trend) < .001). Results were robust to adjustment for prediagnosis physical activity. CONCLUSIONS: Physical activity was associated with lower risk of death following diagnosis. Increased pre- to postdiagnosis activity corresponding to at least 1-3 h/wk of walking was associated with lower risk of death. These results provide further impetus for women to increase their activity after a breast cancer diagnosis, though reverse causation cannot be fully excluded.