Howard R, Leitzmann M, Linet M, Freedman D.. Physical activity and breast cancer risk among pre- and postmenopausal women in the U.S. Radiologic Technologists cohort. Cancer Causes Control 20: 323-333

Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch, National Cancer Institute/NIH, Executive Plaza South, Bethesda, MD, 20892, USA.
Cancer Causes and Control (Impact Factor: 2.74). 11/2008; 20(3):323-33. DOI: 10.1007/s10552-008-9246-2
Source: PubMed


To clarify aspects of the association between physical activity and breast cancer, such as activity intensity required, and possible effect modification by factors such as menopausal hormone therapy (MHT) use. We prospectively examined physical activity in relation to breast cancer risk among 45,631 women participating in the U.S. Radiologic Technologists cohort. Participants provided information at baseline regarding hours spent per week engaging in strenuous activity, walking/hiking for exercise, and walking at home or work. We estimated multivariable relative risks (RR) and 95% confidence intervals (CI) of breast cancer using Cox regression. We identified 864 incident-invasive breast cancers. Greatest risk reduction was observed among women who reported walking/hiking for exercise 10 or more hours per week (RR, 0.57; 95% CI, 0.34-0.95) compared with those reporting no walking/hiking. The association between walking/hiking for exercise and breast cancer was modified by MHT use (p for interaction = 0.039). Postmenopausal women who never used MHT had reduced risks of breast cancer associated with physical activity whereas no relation was observed among ever users of MHT. Our study suggests moderate intensity physical activity, such as walking, may protect against breast cancer. Further, the relation between physical activity and breast cancer may be modified by MHT use.

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    • "This association was stronger for women with a BMI less than 25 kg/m2, premenopausal women, and for ER-/PR- breast tumors [15]. However, our results on postmenopausal breast cancer are in agreement with previous investigations on postmenopausal breast cancer or hormone receptor status and total PA by self-administered questionnaire, which detected no association, or only weak associations after adjusting for confounding factors [5,6,40-45]. In a previous prospective study of Norwegian women, the findings in postmenopausal women did not confirm any effect of PA during leisure time or at work [46]. "
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    ABSTRACT: The relationship between physical activity (PA) throughout life and the risk of postmenopausal breast cancer overall and by estrogen receptor (ER) and progesterone receptor (PR) status, has been reported, but without consistent results. The present study aimed to investigate PA from young age to adulthood in participants of the Norwegian Women and Cancer (NOWAC) Study, in order to determine whether changes in PA level affect the risk of postmenopausal breast cancer. 1767 invasive breast cancer cases were identified among 80,202 postmenopausal participants of the NOWAC Study during 8.2 years of median follow-up. PA levels at age 14 years, 30 years and at cohort enrollment were obtained via a self-administered questionnaire. Multivariate Cox proportional hazard regression models were used to estimate relative risks and 95% confidence intervals of the risk of postmenopausal breast cancer overall and by ER/PR status. Risk of postmenopausal breast cancer overall and by ER/PR status was not associated with physical activity level at enrollment. Women with a low PA level at age 30 had an increased risk of ER+/PR + breast tumors (P for trend = 0.04) compared to women with a moderate physical activity level at age 30. Women with a low physical activity level at all three periods of life had a 20% significantly reduced risk of postmenopausal breast cancer, as well as a reduced risk of ER+/PR + and ER+/PR- breast tumors, compared with women who maintained a moderate physical activity level. However, when analyses were corrected for multiple tests, the result was no longer statistically significant. The findings were consistent over strata of age, body mass index and use of hormone replacement therapy. The study results from this large Norwegian cohort do not support an association between physical activity at different periods of life and the risk of postmenopausal breast cancer.
    Full-text · Article · Mar 2014 · Journal of Negative Results in BioMedicine
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    • "Unlike the two previously mentioned cohorts (Dallal et al., 2007; Leitzman et al., 2008), these results did not vary by receptor subtype of the tumor. Analysis of the US Radiologic Technologists cohort also confirms reductions in risk among physically active women, showing that those who walked or hiked at least 10 h per week had the greatest reductions in risk compared with those not participating in these activities (Howard et al., 2009). Importantly, the association for postmenopausal women was modified by hormone therapy with risk reductions restricted to women who had never used hormone therapy, a finding that has been previously reported (Patel et al., 2003a). "
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    ABSTRACT: During the 1970s and 1980s, a number of factors emerged that were associated with the risk of breast cancer. The majority of these were not modifiable factors and, although much had been learned about breast cancer risk, this information could not be easily translated into recommendations to women for lowering their breast cancer risk. These factors were considered in developing the hypothesis that physical activity would be associated with breast cancer risk, with women who participated consistently in exercise activity having lower risk than inactive women. Since the mid-1990 s a large series of case-control studies and cohort studies have confirmed that physical activity is a modifiable risk factor for breast cancer. Further, when physical activity is a persistent lifestyle practice, reductions in risk are quite clear, with vigorous activities possibly more protective against breast cancer than moderate forms of activity. Thus, maintaining a physically active lifestyle, which has broad health benefits, additionally has the potential to lower breast cancer risk.
    Preview · Article · Dec 2008 · Oncogene
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    ABSTRACT: BRCA1/2 mutation carriers have a high lifetime risk of developing breast cancer. Differences in penetrance indicate that this risk may be influenced by lifestyle factors. Because physical activity is one of the few modifiable risk factors, it may provide a target to add to breast cancer prevention in this high-risk population. We examined the association between self-reported lifetime sports activity and breast cancer risk in a nationwide retrospective cohort study, including 725 carriers, of whom 218 had been diagnosed with breast cancer within 10 years prior to questionnaire completion. We found a nonsignificantly decreased risk for ever engaging in sports activity (HR = 0.84, 95%CI = 0.57–1.24). Among women who had participated in sports, a medium versus low level of intensity and duration (i.e., between 11.0 and 22.7 mean MET hours/week averaged over a lifetime) reduced the risk of breast cancer (HR = 0.59, 95%CI = 0.36–0.95); no dose–response trend was observed. For mean hours/week of sports activity, a nonsignificant trend was observed (HRlow versus never = 0.93, 95%CI = 0.60–1.43; HRmedium versus never = 0.81, 95%CI = 0.51–1.29; HRhigh versus never = 0.78, 95%CI = 0.48–1.29; p trend overall = 0.272; p trend active women = 0.487). For number of years of sports activity no significant associations were found. Among women active in sports before age 30, mean MET hours/week showed the strongest inverse association of all activity measures (HRmedium versus low = 0.60, 95%CI = 0.38–0.96; HRhigh versus low = 0.58, 95%CI = 0.35–0.94; p trend = 0.053). Engaging in sports activity after age 30 was also inversely associated with breast cancer risk (HR = 0.63, 95%CI = 0.44–0.91). Our results indicate that sports activity may reduce the risk of breast cancer in BRCA1/2 mutation carriers.
    Full-text · Article · Feb 2010 · Breast Cancer Research and Treatment
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