Estrogens are natural hormones. They are important in sexual development and other body functions.
Before menopause, most estrogens are produced in the ovaries. After menopause, the ovaries no longer produce much estrogen and estrogens mainly come from fat tissue.
Higher amounts of estrogen in the blood are linked to an increased risk of breast cancer in women after menopause .
Researchers are studying a possible link to breast cancer before menopause.
For a summary of research studies on estrogen levels and the risk of breast cancer, visit the Breast Cancer Research Studies section.
Studies have shown postmenopausal women with higher blood levels of the estrogen estradiol have an increased risk of breast cancer [19,57-59].
A pooled analysis of data from 9 studies found the risk of breast cancer was twice as high among women with higher levels of estradiol compared to women with lower levels .
At this time, health care providers don't use blood estrogen levels to assess breast cancer risk. However, this measure may be useful in the future [61-63].
Certain factors may increase breast cancer risk by affecting estrogen levels.
Body weight is an important example. Estrogen is produced in fat tissue. In general, higher weight means more fat tissue and higher estrogen levels. This likely explains, at least in part, the increased breast cancer risk in women who are heavy after menopause.
Learn more about body weight and breast cancer risk.
A pooled analysis of data from 7 studies found higher blood estrogen levels may modestly increase breast cancer risk before menopause .
Studies in premenopausal women are a challenge to do because estrogen levels vary over the menstrual cycle.
For example, in the early phase of the menstrual cycle (follicular phase), estrogen levels are much lower than in the late phase (luteal phase).
Blood estrogen levels are affected by many factors. Some of these are under your control.
All women can lower their estrogen levels by :
All of these steps may help lower the risk of breast cancer and other chronic diseases.