Factors inside and outside our bodies affect our health. Those outside our bodies are often called environmental factors. There is no one scientific definition for the term “environment.” In health research, different scientists may use different categories when deciding whether a risk is environmental.
Environmental factors may include things found in nature that we eat, drink, touch or breathe, as well as man-made factors. Possible examples include exposures that are passive (such as sunlight or secondhand smoke) and those that are active (such as eating fruits and vegetables or drinking alcohol). Even medications, such as birth control pills or menopausal hormone therapy (postmenopausal hormones), are sometimes considered environmental exposures.
Factors such as age, the hormones produced in our bodies (such as estrogen) and family history are considered to be personal or genetic factors rather than environmental factors. However, they can interact with environmental factors and affect our health.
Some factors in our environment help keep us healthy. Others can increase our risk of breast cancer or other diseases. Still others have little, if any, affect on our health.
Researchers can use different types of studies to learn about the environment and breast cancer risk (learn more).
To learn more about the role of the environment in breast cancer, Komen sponsored a study from the Institute of Medicine (IOM), "Breast Cancer and the Environment, a Life Course Approach" .
The IOM reviewed the scientific evidence on environmental factors and concluded:
- Environmental factors with consistent evidence on a link with an increased risk of breast cancer were:
- Use of menopausal hormone therapy containing estrogen and progestin
- Exposure to ionizing radiation (from medical diagnostic procedures, like CT scans, for example)
- Being overweight (for postmenopausal women)
- Drinking alcohol
- An environmental factor with consistent evidence on a link with an decreased risk of breast cancer was:
- Physical activity (exercise)
- Environmental factors with consistent evidence showing no link with breast cancer risk were:
- Use of hair dye
- Exposure to non-ionizing radiation (from microwave ovens and power lines, for example)
The IOM also identified future needs for breast cancer research on environmental factors including:
- Studies on environmental exposures over the course of a person’s lifetime (as well as preventive behaviors over the course of a lifetime)
- More research into gene and environment interactions
- Better methods of testing chemicals and other agents to know if they are linked to breast cancer