Lifetime Recreational Exercise Activity and Breast Cancer Risk Among Black Women and White Women
Leslie Bernstein, Alpa V. Patel, Giske Ursin, Jane Sullivan-Halley, Michael F. Press, Dennis Deapen, Jesse A. Berlin, Janet R. Daling, Jill A. McDonald, Sandra A. Norman, Kathleen E. Malone, Brian L. Strom, Jonathan Liff, Suzanne G. Folger, Michael S. Simon, Ronald T. Burkman, Polly A. Marchbanks, Linda K. Weiss, Robert Spirtas
Affiliations of authors: Department of Preventive Medicine (LB, GU, JS-H, DD), Department of Pathology (MFP), Keck School of Medicine, University of Southern California, Los Angeles, CA; Department of Nutrition, University of Oslo, Oslo, Norway (GU); Department of Epidemiology and Surveillance Research, American Cancer Society, Atlanta, GA (AVP); Johnson & Johnson Pharmaceutical Research and Development, Titusville, NJ (JAB); Fred Hutchinson Cancer Research Center, Seattle, WA and Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA (JRD, KEM); Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA (JAM, SGF, PAM); Center for Clinical Epidemiology and Biostatistics and Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA (SAN, BLS); School of Public Health, Emory University, Atlanta, GA (JL); Department of Internal Medicine, Karmanos Cancer Institute at Wayne State University, Detroit, MI (MSS); Department of Obstetrics and Gynecology, Baystate Medical Center, Springfield, MA (RTB); Cancer Centers Branch, National Cancer Institute (LKW), Contraception and Reproductive Health Branch, Center for Population Research, National Institute of Child Health and Human Development (RS), National Institutes of Health, Bethesda, MD
Correspondence to: Leslie Bernstein, PhD, Department of Preventive Medicine, USC/Norris Comprehensive Cancer Center, University of Southern California, 1441 Eastlake Ave., Los Angeles, CA 90033 (e-mail: firstname.lastname@example.org).
Background: Physical inactivity is a potentially modifiable breast cancer risk factor. Because few data on this relationship exist for black women, we examined the relationship between breast cancer risk and lifetime and time- or age-specific measures of recreational exercise activity among white women and among black women.
Methods: The Women’s Contraceptive and Reproductive Experiences Study was a multicenter population-based case control study of black women and white women aged 35-64 years with newly diagnosed invasive breast cancer.
We collected detailed histories of lifetime recreational exercise activity during in-person interviews with 4538 case patients with breast cancer (1605 black and 2933 white) and 4649 control subjects (1646 black and 3033 white).
Control subjects were frequency-matched to case patients on age, race, and study site. We examined associations between exercise activity measures (metabolic equivalents of energy expenditure [MET]-hours per week per year) and breast cancer risk overall and among subgroups defined by race, other breast cancer risk factors, and tumor characteristics by use of unconditional logistic regression. All statistical tests were two-sided.
Results: Among all women, decreased breast cancer risk was associated with increased levels of lifetime exercise activity (e.g., average MET-hours per week per year, P trend = .002).
An average annual lifetime exercise activity that was greater than the median level for active control subjects was associated with an approximately 20% lower risk of breast cancer, compared with that for inactivity (for 6.7-15.1 MET-hours/week/year, odds ratio [OR] = 0.82, 95% confidence interval [CI] = 0.71 to 0.93; for 15.2 MET-hours/week/year, OR = 0.80, 95% CI = 0.70 to 0.92).
The inverse associations did not differ between black and white women (for MET-hours/week/year, P trend = .003 and P trend = .09, respectively; homogeneity of trends P = .16). No modification of risk was observed by disease stage, estrogen receptor status, or any breast cancer risk factor other than first-degree family history of breast cancer.
Conclusions: This study supports an inverse association between physical activity and breast cancer among black women and among white women.
Journal of the National Cancer Institute, Vol. 97, No. 22, 1671-1679, November 16, 2005