(HealthDay News) – Women may be able to reduce their risk of breast cancer by avoiding exposure to certain environmental factors, according to a report published December 7, 2011 by the Institute of Medicine.

Irva Hertz-Picciotto, PhD (of the University of California in Davis) and colleagues reviewed current evidence on the relationship of environmental factors (not directly inherited through DNA) with breast cancer, the challenges in investigating them, and potential preventive actions to reduce breast cancer risk.

The investigators found consistent evidence of a link with increased breast cancer risk for use of combined estrogen and progestin hormone therapy, exposure to ionizing radiation, excess weight in postmenopausal women, and alcohol consumption; there was some evidence for physical activity decreasing the risk. They found mixed views on the connection between smoking and breast cancer, and possible associations for other factors, such as secondhand smoke and nighttime shift work. For certain environmental agents, such as bisphenol A, there was a clear mechanism in animals, but studies in humans were lacking or inadequate. Research challenges included lack of understanding about breast development and the origins and progression of breast cancer, early lifetime exposures, the ethical challenges posed by randomized controlled clinical trials, and limitations of animal studies. Preventive actions to reduce breast cancer risk included avoiding unnecessary medical radiation, postmenopausal combined hormone therapy, and smoking; limiting alcohol consumption; increasing physical activity; and minimizing weight gain, particularly for postmenopausal women.

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“The potential risk reductions from any of these actions for any individual woman will vary and may be modest,” the authors write.

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