An overabundance of estrogen also leads to other problems. It can slow the body's ability to break down fat, cause water retention, throw off blood sugar levels and even reduce the amount of oxygen the lungs and cells take in. In the l980s and 1990s, medical researchers discovered that excessive estrogen can cause even more far-reaching complications—endometriosis, uterine fibroids, uterine cancer, cervical dysplasia, breast cysts and many breast cancers are all thought to have some connection to high estrogen levels. To further complicate matters, there is more than one kind of estrogen in the body, and not all types are carcinogenic (cancer-causing). A specific problem may not be related to all types of estrogen, but specifically to one troublesome kind that tends to be more carcinogenic than the others.