Journal of the National Cancer Institute Advance Access published online on May 13, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn135
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© The Author 2008. Published by Oxford University Press.
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A Prospective Study of Age-Specific Physical Activity and Premenopausal Breast Cancer
Affiliations of authors: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA (SSM, WCW, DF, BR, GAC); Departments of Epidemiology (SSM, WCW, GAC) and Nutrition (SSM, WCW), Harvard School of Public Health, Boston, MA; Department of Epidemiology, University of Washington, Seattle, WA (SSM); Cancer Prevention Program, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA (SSM); Department of Surgery, Washington University School of Medicine, St Louis, MO (GAC)
Correspondence to: Sonia S. Maruti, MSc, ScD, Cancer Prevention Program, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N., M4-B402, Seattle, WA 98109-1024 (e-mail: smaruti{at}fhcrc.org).
Background: Physical activity has been consistently associated with lower risk of postmenopausal breast cancer, but its relationship with premenopausal breast cancer is unclear. We investigated whether physical activity is associated with reduced incidence of premenopausal breast cancer, and, if so, what age period and intensity of activity are critical.
Methods: A total of 64 777 premenopausal women in the Nurses’ Health Study II reported, starting on the 1997 questionnaire, their leisure-time physical activity from age 12 to current age. Cox regression models were used to examine the relationship between physical activity, categorized by age period (adolescence, adulthood, and lifetime) and intensity (strenuous, moderate, walking, and total), and risk of invasive premenopausal breast cancer.
Results: During 6 years of follow-up, 550 premenopausal women developed breast cancer. The strongest associations were for total leisure-time activity during participants’ lifetimes rather than for any one intensity or age period. Active women engaging in 39 or more metabolic equivalent hours per week (MET-h/wk) of total activity on average during their lifetime had a 23% lower risk of premenopausal breast cancer (relative risk = 0.77; 95% confidence interval = 0.64 to 0.93) than women reporting less activity. This level of total activity is equivalent to 3.25 h/wk of running or 13 h/wk of walking. The age-adjusted incidence rates of breast cancer for the highest (
54 MET-h/wk) and lowest (<21 MET-h/wk) total lifetime physical activity categories were 136 and 194 per 100 000 person-years, respectively. High levels of physical activity during ages 12–22 years contributed most strongly to the association.
Conclusions: Leisure-time physical activity was associated with a reduced risk for premenopausal breast cancer in this cohort. Premenopausal women regularly engaging in high amounts of physical activity during both adolescence and adulthood may derive the most benefit.
| CONTEXT AND CAVEATS Prior knowledge Physical activity is associated with reduced risk of breast cancer among postmenopausal women. Study design Cohort study of premenopausal nurses who were surveyed about the type and duration of leisure-time physical activity they engaged in during their lifetime and were monitored for breast cancer for 6 years. Contributions Average lifetime physical activity equivalent to 3.25 h/wk of running or 13 hours per week of walking was associated with a reduced risk for breast cancer compared with less activity (136 vs 196 breast cancers per 100 000 person-years). High amounts of physical activity during ages 12–22 were the most important. Implications In this cohort, women who regularly engaged in high amounts of physical activity during adolescence and early adulthood had a lower risk of premenopausal breast cancer than women who engaged in less activity. Limitations The results are likely to be generalizable only to premenopausal white women. Nearly 90% of the women in the cohort also regularly engaged in regular occupational physical activity (walking). Other lifestyle behaviors may also be important. In addition, the physical activity data were based on recall.
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Manuscript received November 30, 2007; revised March 3, 2008; accepted March 28, 2008.
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J Natl Cancer Inst 2008 100: 687.
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  Lifetime Physical Activity and Risk for Premenopausal Breast Cancer Journal Watch Women's Health, July 3, 2008; 2008(703): 1 - 1. [Full Text]
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