Estradiol is a female sex hormone necessary for many processes in the body. It is also present in males, but at lower levels. Estradiol is a form of estrogen, which has not only a critical impact on reproductive and sexual functioning, but also affects other organs including the bones. Like other steroids, estradiol is derived from cholesterol. After side chain cleavage and utilizing the delta-5 pathway or the delta-4 pathway, androstenedione is the key intermediary. A fraction of the androstenedione is converted to testosterone, which in turn undergoes conversion to estradiol by an enzyme called aromatase. In an alternative pathway, androstenedione is "aromatized" to estrone, which is subsequently converted to estradiol.
Estradiol increases the risk of developing endometrial hyperplasia, which is a condition that may lead to cancer of the uterus. To lower this risk of developing endometrial hyperplasia, it is adviced to take progestins. Estradiol has a profound effect on bone. If severe side-effects of low levels of estradiol in a woman's blood are experienced at the beginning of menopause, hormone replacement therapy may be prescribed. Often such therapy is combined with a progestin. Estrogen therapy may also be used in treatment of infertility in women when there is a need to develop sperm-friendly cervical mucus or an appropriate uterine lining.
Individuals without estradiol will become tall and eunuchoid as epiphysieal closure is delayed or may not take place. Bone structure is affected resulting in early osteopenia and osteoporosis. Also, women past menopause experience an accelerated loss of bone mass due to a relative estrogen deficiency.