Testosterone is the main hormone that regulates muscle strength, fat burning, and more functions in men and women.
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 a 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 glands. 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).
Diseases and Conditions That Affect Testosterone
Men can experience a drop in testosterone due to conditions or diseases affecting the:
- Testes – direct injury, castration, infection, radiation treatment, chemotherapy, tumors.
- Pituitary and hypothalamus glands – tumors, medications (especially steroids, morphine or related drugs, and major tranquilizers, such as haloperidol), HIV/AIDS, certain infections, and autoimmune conditions.
Genetic diseases, such as Klinefelter syndrome (in which a man has an extra x-chromosome) and hemochromatosis (in which an abnormal gene causes excessive iron to accumulate throughout the body, including the pituitary gland) can also affect testosterone.
Women may have a testosterone deficiency due to diseases of the pituitary, hypothalamus, or adrenal glands, in addition to removal of the ovaries. Estrogen therapy increases sex hormone-binding globulin and, like aging men, this reduces the amount of free, active testosterone in the body.
Currently, testosterone therapy is approved primarily for the treatment of delayed male puberty, low production of testosterone (whether due to failure of the testes, pituitary, or hypothalamus function), and certain inoperable female breast cancers.
However, it is quite possible that testosterone treatment can improve symptoms in men with significantly low levels of active (free) testosterone, such as:
- generalized weakness;
- low energy;
- disabling frailty;
- problems with sexual function;
- problems with cognition.
However, many men with normal testosterone levels have similar symptoms so a direct connection between testosterone levels and symptoms is not always clear. As a result, there is some controversy about which men should be treated with supplemental testosterone.
Testosterone therapy may make sense for women who have low testosterone levels and symptoms that might be due to testosterone deficiency. (It’s not clear if low levels without symptoms are meaningful; treatment risks may outweigh benefits.)
However, the wisdom and effectiveness of testosterone treatment to improve sexual function or cognitive function among postmenopausal women is unclear.
People with normal testosterone levels are sometimes treated with testosterone at the recommendation of their doctors or they obtain the medication on their own. Some have recommended it as a “remedy” for aging.
For example, a study from Harvard Medical School in 2003 found that even men who started out with normal testosterone results noted the loss of fat, increased muscle mass, better mood, and less anxiety when receiving testosterone therapy.
Similar observations have been noted among women. However, the risks and side effects of taking testosterone when the body is already making enough still discourage widespread use.
The Bottom Line
Testosterone is so much more than its reputation would suggest. Men and women need the proper amount of testosterone to develop and function normally. However, the optimal amount of testosterone is far from clear.
Checking testosterone levels is as easy as having a blood test. The difficult part is interpreting the result. Levels vary over the course of the day.
A single low level may be meaningless in the absence of symptoms, especially if it was normal at another time.
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