As noted in Chapter 1, the committee adopted a broad interpretation of the environment that encompasses all factors that are not directly inherited through DNA. This definition allows for the consideration of a broad range of factors that may be encountered at any time in life and in any setting: the physiologic and developmental course of an individual, diet and other ingested substances, physical activity, microbial agents, physical and chemical agents encountered at home or work, medical treatments and interventions, social factors, and cultural practices. Figure 2-4 illustrates the multiple levels of biologic and social organization through which potential environmental exposures can influence breast cancer, and Figure 2-5 illustrates one approach to integrating this socio-ecologic perspective into investigation of potential contributions to breast cancer over the life course.

Many of these environmental influences overlap. For example, the physical environment encompasses medical interventions, dietary exposures to nutrients, energy and toxicants, ionizing radiation, and chemicals from industrial and agricultural processes and from consumer products. These in turn are influenced by the social environment, because cultural and economic factors influence diet at various stages of life, reproductive choices, energy balance, adult weight gain, body fatness, voluntary and involuntary physical activity, medical care, exposure to tobacco smoke and alcohol, and


FIGURE 2-4 Multiple levels on which environmental exposures may act to influence breast cancer.

SOURCE: Personal communication, R. A. Hiatt, University of California, San Francisco, September 16, 2010.

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