Testosterone, which is produced in the body by the male testes, influences men physically, emotionally and sexually. Sometimes called the "king of hormones", testosterone is certainly the most important hormone when it comes to sexual characteristics in men.
Role of testosterone
The group of male hormones that create and support masculinity is known as androgens, but testosterone is the one that is primarily responsible for:
- Determining before birth whether a baby will develop into a boy or a girl
- Influencing sexual preferences
- Forming personalities into poets, athletes, competitors or co-operators
- Regulating the sex drive in men (and in women)
- Starting and maintaining the development of male sexual characteristics including dominance, emotional and physical strength, body shape, hairiness, deep voice, and even odor
- Governing sperm production and quality
- The ability to perform adequately during sexual intercourse
Testosterone plays a role in developing creativity, intellect, thought patterns, assertiveness and drive, as well as the ability to propose new ideas and carry them through to successful conclusions. Testosterone also affects general health during childhood, adolescence and adulthood. Adequate levels of testosterone throughout life help males to thrive as children, develop stronger muscles and bones (along with acne) during puberty, cope with stress during peak career years, and age gracefully after retirement.
Testosterone production in the body
This important hormone is produced mainly in the testes in males (more than 95 percent) and in the ovaries in females; however, small amounts are made in the outer layer of the adrenal glands in both sexes. The process that carefully regulates the amount and timing of testosterone production is complex and begins in the brain. When a man feels aroused or successful, the cerebral cortex, the most sophisticated area of the brain, sends a signal to another part of the brain called the hypothalamus to stimulate the production of testosterone. The hypothalamus is an area at the base of the brain that regulates much of the body's hormonal activity. It does this by sending chemical signals to the pituitary gland, a cherry-sized organ that produces a wide variety of hormones involved in the regulation of growth, thyroid function, blood pressure, pregnancy, birth and other critical body functions.
To stimulate testosterone production, the hypothalamus releases a substance to the pituitary gland called gonadotropin-releasing hormone (GnRH). This hormone, in turn, causes the gland to produce two other hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), collectively known as gonadotropins. LH is released into the bloodstream where it travels to the male testes and triggers the production of testosterone from cholesterol. If this process continues until the testosterone level becomes too high, the pituitary slows the release of LH so production slows down. FSH is similarly involved in the increase and decrease in sperm production.
When LH reaches the testes, it influences activity in the Leydig cells, which are where cholesterol is gradually changed into a series of compounds until it becomes testosterone. When the small but vital amount of testosterone produced is released into the bloodstream, it is mostly bound to a special "carrier" compound called sex hormone binding globulin or SHBG. SHBG, which is produced by the liver, plays an important role in regulating the amount of "free" testosterone circulating in the body at any one time. The more SHBG there is the less unbound, active testosterone is able to move from the blood stream into cells where it is needed. As SHBG levels rise and fall, so do free testosterone levels, except in reverse.
With such a complex chain of events leading to a normal testosterone level, many problems or interruptions along the process can lead to sub-normal or low testosterone levels in men at any age. If there are diseases or negative conditions involving the male testes, hypothalamus, pituitary gland or genetic material, the resulting state is called hypogonadism.
Causes of low testosterone
A variety of conditions can cause low testosterone besides aging:
- The testes may be damaged, especially the Leydig cells, during sports or from other physical trauma.
- A case of mumps after puberty can cause an inflammation of the testes that interferes with testosterone and sperm production.
- Radiation treatment or chemotherapy can have a negative effect on the Leydig cells.
- Testicular or pituitary tumors can also have an impact on the testosterone level.
- HIV/AIDs and other serious viral infections can inflict damage on the pituitary gland, the hypothalamus or the testes.
- Genetic conditions such as Klinefelter's, Kallmann's and Prader-Willi syndromes and myotonic dystrophy all can have a negative impact on testosterone production.
- Vasectomy may damage the Leydig cells and lead to early andropause and low testosterone levels.
In addition, many lifestyle habits affect the way testosterone is produced. A diet high in meat and poultry may expose a man to hormones used in meat production that act like estrogen in the body. Estrogen is a potent inhibitor of testosterone production as are prolonged periods of high stress. Mild to moderately intense physical stress, as in casual sports and sexual intercourse, may actually boost testosterone production. Alcohol consumption, on the other hand, has been proven to have a strong negative impact on testosterone levels. Beer, which contains plant estrogens, is particularly toxic to the male testes. As we all know, the testes are very heat sensitive so switching from jockey shorts and tight jeans to boxers and loose pants may raise the testosterone level.
If you are feeling the effects of low testosterone, you will benefit from knowing how testosterone is produced and how lifestyle habits can affect testosterone production.
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Posted February 2004
Updated February 2013