Testosterone — What It Does And Doesn't Do

When you think of testosterone, what comes to mind? Macho men? Aggressive, impatient, type A behavior? Road rage? Violence?

Testosterone's role in bad behavior is largely a myth. What's more, testosterone plays other important roles in health and disease that may surprise you. For example, did you know that testosterone is a key player in prostate cancer? Or, that women need testosterone, too? There's more to testosterone than guys behaving badly.

Testosterone's Role

Testosterone is the major sex hormone in males and plays a number of important roles, such as:

• The development of the penis and testes

• The deepening of the voice during puberty

• The appearance of facial and pubic hair starting at puberty; later in life, it may play a role in balding

• Muscle size and strength

• Bone growth and strength

• Sex drive (libido)

• Sperm production

Adolescent boys with too little testosterone may not experience normal masculinization. For example, the genitals may not enlarge, facial and body hair may be scant and the voice may not deepen normally.

Testosterone may also help maintain normal mood. There may be other important functions of this hormone that have not yet been discovered.

Signals sent from the brain to the pituitary gland at the base of the brain control the production of testosterone in men. The pituitary gland then relays signals to the testes to produce testosterone. A "feedback loop" closely regulates the amount of hormone in the blood. When testosterone levels rise too high, the brain sends signals to the pituitary to reduce production.

If you thought testosterone was only important in men, you'd be mistaken. Testosterone is produced in the ovaries and adrenal gland. It's one of several androgens (male sex hormones) in females. These hormones are thought to have important effects on:

• Ovarian function

• Bone strength

• Sexual behavior, including normal libido (although evidence is not conclusive)

The proper balance between testosterone (along with other androgens) and estrogen is important for the ovaries to work normally. While the specifics are uncertain, it's possible that androgens also play an important role in normal brain function (including mood, sex drive and cognitive function).