• Behavioral and Epidemiology Research Group, American Cancer Society, Atlanta, GA, USA.
• Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA.
• Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
• Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA. ssteck@sc.edu.

PURPOSE: Healthy or unhealthy lifestyle behaviors are often adopted together. We aimed to investigate the combined effect of estrogen-related lifestyle factors on postmenopausal breast cancer risk.

METHODS: Data from 27,153 women enrolled in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial were used. We created an estrogen-related lifestyle score (ERLS) by incorporating a previously developed measure of estrogenic diet, alcohol intake, body mass index (BMI), and physical activity. The scores ranged from 0 to 6 with alcohol and BMI accounting for higher weights than the other factors. To evaluate the preventive possibilities of a low estrogen-related lifestyle and to be consistent with other published lifestyle scores, higher scores were set to correspond with potentially lower estrogenic lifestyle. The association between the ERLS and incident breast cancer was examined using Cox proportional hazards models.

RESULTS: Participants with an ERLS of 4 or ≥ 5 had a 23% (HR 0.77; 95% CI 0.67-0.89) and 34% (HR 0.66; 95% CI 0.56-0.78) lower risk of breast cancer, respectively, compared to those with an ERLS ≤ 2 after multivariable adjustment. Estimates were similar when restricting to invasive cases or estrogen receptor-positive subtypes. No single lifestyle component appeared to drive the association.

CONCLUSIONS: Our findings suggest that the combined effect of a lifestyle characterized by a low estrogenic diet, low alcohol consumption, low body weight, and high levels of physical activity are associated with a reduction in postmenopausal breast cancer risk, possibly through an influence on estrogen metabolism.