Abstract B142: Physical activity and risk of breast cancer among postmenopausal women

B142

Physical activity is beneficial for many reasons, including weight loss and maintenance, improved insulin sensitivity, and improved lipid profile. Studies of the effect of physical activity on the risk of breast cancer have had conflicting results. We assessed the associations of specific activities and total activity within the prospective Nurses’ Health Study cohort. Amount and type of physical activity was queried every two to four years starting in 1986. The specific activities included walking, jogging, running, swimming, bicycling, tennis, aerobics, lawn mowing, yoga, and arm or leg weights. Total activity was calculated as the sum of time spent doing each individual activity. Cumulative averages were calculated for each 2-year follow-up period. Cox proportional hazards models, adjusting for age, follow-up period, and several breast cancer risk factors, were used to calculate relative risks (RR) and 95% confidence intervals (CI). A total of 95,485 postmenopausal women were followed for up to 20 years (1986-2006). Overall 4,810 cases of invasive breast cancer were documented during follow-up. Compared with those whose total activity summed to less than 10 minutes per day, women who engaged in higher amounts of total physical activity were at lower risk of breast cancer (RR (95%CI) were 1.00 (0.92-1.08) for 10-<20 mins/day, 0.91 (0.84-1.00) for 20-<30 mins/day, 0.92 (0.85-1.00) for 30-<60 mins/day, and 0.87 (0.79-0.97) for ≥60 mins/day, p-trend=0.004). When easy walking (<3 m.p.h.), brisk walking (≥3 m.p.h.), jogging or running, and all other activities were assessed in the same statistical model, only brisk walking was associated with a significant decreased risk of breast cancer (RR (95%CI) were 0.95 (0.87-1.05) for 10-<20 mins/day, 0.95 (0.85-1.07) for 20-<30 mins/day, 0.89 (0.79-1.01) for 30-<60 mins/day, and 0.81 (0.63-1.05) for ≥60 mins/day, p-trend=0.014). The associations with total activity and with brisk walking were apparent for breast tumors that were positive for estrogen and progesterone receptors (ER+/PR+) (N=2,434) but not for ER-/PR- tumors (N=646). These data suggest that total activity, and particularly brisk walking, may be associated with a reduced risk of breast cancer, and may act along a hormonal pathway.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):B142.