标题：Beyond Recreational Physical Activity: Examining Occupational and Household Activity, Transportation Activity, and Sedentary Behavior in Relation to Postmenopausal Breast Cancer Risk
摘要：Objectives. We prospectively examined nonrecreational physical activity and sedentary behavior in relation to breast cancer risk among 97 039 postmenopausal women in the National Institutes of Health–AARP Diet and Health Study. Methods. We identified 2866 invasive and 570 in situ breast cancer cases recorded between 1996 and 2003 and used Cox proportional hazards regression to estimate multivariate relative risks (RRs) and 95% confidence intervals (CIs). Results. Routine activity during the day at work or at home that included heavy lifting or carrying versus mostly sitting was associated with reduced risk of invasive breast cancer (RR = 0.62; 95% CI = 0.42, 0.91; P trend = .024). Conclusions. Routine activity during the day at work or home may be related to reduced invasive breast cancer risk. Domains outside of recreation time may be attractive targets for increasing physical activity and reducing sedentary behavior among postmenopausal women. Adult women in the United States aged 50 to 69 years spend on average about 8 waking hours per day being inactive. 1 Recreational physical activity has an established relation to reduced risk of postmenopausal breast cancer 2 – 4 as well as preventing weight gain, type 2 diabetes, metabolic syndrome, high blood pressure, coronary heart disease, stroke, and early death. 3 However, the relationship between postmenopausal breast cancer and physical activity outside of recreation time, in the domains of home, occupation, and transportation, 5 has been examined less extensively. Occupational cohort studies 6 – 8 lack ideal control for potential confounding variables, but they have tended to support an inverse relationship between nonrecreational physical activity and breast cancer. In some prospective cohort studies, women who, on average, engaged in higher levels of household activity each week had lower risk of invasive breast cancer 9 , 10 ; in others, however, no relationship was observed between risk of invasive breast cancer and either nonrecreational 11 , 12 or occupational physical activity. 9 , 13 , 14 At present, the extent to which sedentary behavior is associated with breast cancer risk has not been examined prospectively. Sedentary behavior is ubiquitous in the daily routines of modern adults 15 and has emerged as a new focus for research on physical activity and health. 16 – 21 It has been proposed that too much sitting may be distinct from too little moderate–vigorous recreational physical activity. 19 Sedentary behavior may independently reduce overall energy expenditure, 22 leading to adverse effects on insulin sensitivity, fat storage, 23 and estrogen metabolism, 24 pathways that are relevant to breast cancer development. The study of nonrecreational physical activity and sedentary behavior in relation to breast cancer could prove fruitful because these exposures have been related to risk of other chronic conditions among women and may work through similar pathways. Independent of recreational moderate–vigorous physical activity, standing and walking around the home have been inversely associated with chronic conditions such as obesity and diabetes, 25 and walking and bicycling to work have been inversely associated with all-cause mortality 26 – 28 and obesity. 29 Sedentary behavior has been positively associated with obesity, 30 , 31 weight gain, 25 diabetes, 30 all-cause mortality, 32 – 34 cardiovascular disease mortality, 32 – 34 cancer mortality, 32 and mortality from other causes. 32 Among women, television watching has been positively associated with increases in obesity and diabetes. 15 Breaks in sedentary behavior have been associated cross-sectionally with beneficial changes in biomarkers of metabolic risk such as waist circumference, adiposity, triglycerides, and 2-hour plasma glucose. 35 We explored the associations of occupational and household activity, transportation activity (i.e., walking or bicycling to work), and sedentary behavior in relation to breast cancer risk in the National Institutes of Health (NIH)–AARP Diet and Health Study. We hypothesized that (1) occupational and household activity and transportation activity are inversely associated with risk of invasive breast cancer and (2) sedentary behavior is positively associated with risk of invasive breast cancer. We planned a priori to explore these hypotheses for in situ breast cancer as well.
