Estrogen levels vary on a day-to-day basis during different cycles in the menstrual period as well as during normal stages of female development, so there is no single estrogen level considered normal, according to WebMD. Estrogen levels rise during puberty and a healthy pregnancy and fall during menopause.
In addition to menopause, many factors can contribute to a decrease in estrogen levels, including low body fat, extreme exercise, eating disorders, hypogonadism, hypopituitarism, pregnancy failure and polycystic ovarian syndrome, according to WebMD. High estrogen levels during puberty enable a young woman's sexual development, increasing breast size, hip width and body hair. High estrogen levels are also common among obese women and individuals with high blood pressure and diabetes.