Estradiol is a naturally occurring byproduct of cholesterol metabolism (by way of testosterone) and is vital to the maintenance of fertility and secondary sex characteristics in females.

It is the primary estrogen in humans. Among its functions and effects:

• Breast development and maintenance
• Adding fat to breasts, hips, thighs during puberty
• Improving bone strength and density
• Accelerating bone maturation and bringing epiphyses to closure, completing growth
• Growth of the uterus
• Development of the endometrial lining to a thickness necessary to support pregnancy and menstruation
• Promoting and maintaining vaginal mucosal thickness and secretions
• Serving as the primary feedback to the brain of sex hormone levels in both males and females.

Most estradiol in women is produced by the granulosa cells of the ovaries by aromatization of testosterone from the theca cells. Smaller amounts of estradiol are also produced by the adrenal cortex. An additional source of estradiol in both sexes is peripheral aromatization of testosterone to estradiol.

One of the fascinating twists to mammalian sexual differentiation is that estradiol is one of the two active metabolites of testosterone in males (the other being dihydrotestosterone). Estradiol cannot be transferred readily from the circulation into the brain. Since fetuses of both sexes are exposed to similarly high levels of maternal estradiol, it can play little role in prenatal sexual differentiation. However, testosterone enters the central nervous system more freely and significant amounts are aromatized to estradiol within the brain of most male mammals, including humans. There is now much evidence that the programming of adult male sexual behavior in "lower mammals," (such as mounting rather than lordosis behavior), is largely dependent on estradiol produced in the central nervous system during prenatal life and early infancy from testosterone. We do not yet know whether this process plays a minimal or significant part in human sexual behaviors.

In the event that levels of estradiol in a woman's blood are low (possibly due to menopause, oophorectomy, transsexuality, etc.), a hormone replacement therapy may be prescribed, including drugs such as Premarin™, Estrofem™, or Estrace™.

See Also

• estrogen insensitivity syndrome
• hormone replacement therapy
• gender
• androgen