Coffee contains numerous phytoestrogens, which are chemicals found in plants that sometimes act like the hormone estrogen in your body. The role that phytoestrogens play in your body varies, however, with some mimicking estrogen and having the same effects as this hormone and others blocking estrogen's effects. Coffee appears to have both varieties and factors like its preparation method – filtering or boiling – may influence how much of each type you take in, according to a 2011 study in "Breast Cancer Research."
Phytoestrogens and their impact on the body are of interest because they can alter your risk for health conditions like breast cancer and fertility problems. Phytoestrogens that act as estrogen mimics may affect your body's breakdown or production of estrogen and raise the estrogen levels in your bloodstream. However, not all phytoestrogens mimic estrogen -- and some that mimic it at low doses block it at high doses. Much of the research on phytoestrogens examines the effect they have on breast cancer cells.
In your body, estrogen interacts with a family of proteins that are called estrogen receptors. Estrogen is a chemical messenger that acts as a key and the receptors in your cells act as a lock. For estrogen to deliver its message, or unlock a receptor, it must bind with the lock, or receptor. Phytoestrogens that mimic the estrogen in your body can bind to your estrogen receptors. Phytoestrogens that block estrogen discourage estrogen receptors from unlocking. This is significant when it comes to hormone-sensitive conditions like breast cancer. Breast cancer is divided into two general types. These are hormone-responsive, or estrogen receptor-positive, and non-hormone-responsive, or estrogen-receptor-negative. These are commonly referred to as ER-positive and ER-negative breast cancer. High coffee intake appears to be associated with a reduced risk for ER-negative breast cancer among postmenopausal women, according to Jingmei Li, lead author for the 2011 "Breast Cancer Research" study.
Coffee is a chemically complex beverage containing many compounds that can affect your estrogen levels. One is the phytoestrogen trigonelline, according to a 2009 study published in the "Journal of Nutrition." This phytoestrogen activates estrogen receptors and appears in laboratory studies to promote growth of ER-positive breast cancer cells, notes lead study author K.F. Allred. Meanwhile, coffee significantly contributes to your blood levels of enterolactone, another phytoestrogen that is associated with a significantly reduced risk for ER-negative breast cancer, according to Li. Coffee also contains the phytoestrogen formononetin, which has estrogen-like activity in your body and also is found in black cohosh. Enterolacotone is a lignan, one of the most studied phytoestrogen groups. This group differs from the isoflavones, the group of phytoestrogens that occurs in soybeans. Formononetin is an isoflavone. Trigonelline is an alkaloid.
Some studies demonstrate a negative relation between coffee drinking and estradiol levels in your body, according to E. Petridou, lead study author for a 1992 study in the "Annals of Epidemiology." This is the most important form of estrogen in your body, notes Medline Plus. This inverse relationship may be responsible for the correlation between coffee consumption during pregnancy and lower birth weight, which is well documented in scientific literature, notes Petridou.
How your coffee is roasted and prepared may alter its effect on your estrogen receptors. There is a significant difference between boiled coffee and filtered coffee, for example, according to Li. Boiled coffee appears to afford more protection against ER-negative breast cancer than filtered coffee, Li notes. Also, robusta coffees have six times more isoflavones than Arabica coffees, notes a 2010 study in the "Journal of Agricultural and Food Chemistry."
- “Breast Cancer Research”; Coffee Consumption Modifies Risk of Estrogen-Receptor Negative Breast Cancer; Jingmei Li, et al.; 2011
- “Annals of Epidemiology”; Pregnancy Estrogens in Relation to Coffee and Alcohol Intake; E. Petridou, et al.; 1992
- “Journal of Nutrition”; Trigonelline Is a Novel Phytoestrogen in Coffee Beans; K.F. Allred, et al.; 2009
- “Journal of Agricultural and Food Chemistry”; Isoflavones in Coffee: Influence of Species, Roast Degree, and Brewing Method; Rita C. Alves, et al.; 2010
- “Phytomedicine”; Analysis of Thirteen Populations of Black Cohosh for Formononetin; E.J. Kennelly, et al.; 2002
- Medline Plus: Estradiol; July 2009