Testosterone is the main sex hormone found in men. It controls male physical features. The testes (testicles) make testosterone. Women have testosterone too, but in much smaller amounts than in men.
Testosterone 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 play a role in maintaining normal mood. There may be other important functions of this hormone that have not yet been discovered.
How is testosterone manufactured
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.
In women 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).
Your testosterone levels fluctuate from hour to hour. They tend to be highest in the morning and lowest at night.Testosterone levels are highest by age 20 to 30 and slowly go down after age 30 to 35.
How our testosterone levels affect us
It is most common for men to suffer from low testosterone levels but occasionally levels may become elevated.
Early symptoms and signs of low testosterone in men include:
- Reduced body and facial hair
- Loss of muscle mass
- Low libido, impotence, small testicles, reduced sperm count and infertility
- Increased breast size
- Hot flashes
- Irritability, poor concentration and depression
- Loss of body hair
- Brittle bones and an increased risk of fracture
Later in life, low testosterone can lead to decreased muscle and bone strength, less energy, and lower fertility.
Some things can temporarily lower testosterone, for instance, too much exercise, poor nutrition, or serious illness. Living a healthy lifestyle with regular exercise and a good diet helps maintain normal testosterone levels.
Having too much naturally-occurring testosterone is not a common problem among men. That may surprise you given what people might consider obvious evidence of testosterone excess: road rage, fighting among fathers at Little League games and sexual promiscuity.
Part of this may be due to the difficulty defining “normal” testosterone levels and “normal” behavior. Blood levels of testosterone vary dramatically over time and even during the course of a day. In addition, what may seem like a symptom of testosterone excess (see below) may actually be unrelated to this hormone.
In fact, most of what we know about abnormally high testosterone levels in men comes from athletes who use anabolic steroids, testosterone or related hormones to increase muscle mass and athletic performance.
Problems associated with abnormally high testosterone levels in men include:
- Low sperm counts, shrinking of the testicles and impotence
- Heart muscle damage and increased risk of heart attack
- Prostate enlargement with difficulty urinating
- Liver disease
- Fluid retention with swelling of the legs and feet
- Weight gain, perhaps related in part to increased appetite
- High blood pressure and cholesterol
- Increased muscle mass
- Increased risk of blood clots
- Stunted growth in adolescents
- Uncharacteristically aggressive behavior (although not well studied or clearly proven)
- Mood swings, euphoria, irritability, impaired judgment, delusions
Among women, perhaps the most common cause of a high testosterone level is polycystic ovary syndrome (PCOS). This disease is common. It affects 6% to 10% of premenopausal women.
The ovaries of women with PCOS contain multiple cysts. Symptoms include irregular periods, reduced fertility, excess or coarse hair on the face, extremities, trunk and pubic area, male-pattern baldness, darkened, thick skin, weight gain, depression and anxiety. One treatment available for many of these problems is spironolactone, a diuretic (water pill) that blocks the action of male sex hormones.
Women with high testosterone levels, due to either disease or drug use, may experience a decrease in breast size and deepening of the voice, in addition to many of the problems men may experience.
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.