Testosterone is a hormone found in humans, as well as in other animals. In men, the testicles primarily make testosterone. Women’s ovaries also make testosterone, though in much smaller amounts.
What is Testosterone?
Testosterone is the hormone responsible for the development of male sexual characteristics. Hormones are chemical messengers that trigger necessary changes in the body. Females also produce testosterone, usually in smaller amounts.
It is a type of androgen produced primarily by the testicles in cells called the Leydig cells.
In men, testosterone is thought to regulate a number of functions alongside sperm production. These include:
Muscle size and strength
Red blood cell production
How is testosterone controlled?
The regulation of testosterone production is tightly controlled to maintain normal levels in blood, although levels are usually highest in the morning and fall after that.
The hypothalamus and the pituitary gland are important in controlling the amount of testosterone produced by the testes.
In response to gonadotrophin-releasing hormone from the hypothalamus, the pituitary gland produces luteinising hormone which travels in the bloodstream to the gonads and stimulates the production and release of testosterone.
As blood levels of testosterone increase, this feeds back to suppress the production of gonadotrophin-releasing hormone from the hypothalamus which, in turn, suppresses production of luteinising hormone by the pituitary gland.
Levels of testosterone begin to fall as a result, so negative feedback decreases and the hypothalamus resumes secretion of gonadotrophin-releasing hormone.
What happens if you have too much testosterone?
The effect excess testosterone has on the body depends on both age and sex.
It is unlikely that adult men will develop a disorder in which they produce too much testosterone and it is often difficult to spot that an adult male has too much testosterone.
More obviously, young children with too much testosterone may enter a false growth spurt and show signs of early puberty and young girls may experience abnormal changes to their genitalia.
In both males and females, too much testosterone can lead to precocious puberty and result in infertility.
In women, high blood levels of testosterone may also be an indicator of polycystic ovary syndrome.
Women with this condition may notice increased acne, body and facial hair (called hirsutism), balding at the front of the hairline, increased muscle bulk and a deepening voice.
There are also several conditions that cause the body to produce too much testosterone.
These include androgen resistance, congenital adrenal hyperplasia and ovarian cancer.
What happens if you have too little testosterone?
If testosterone deficiency occurs during fetal development, then male characteristics may not completely develop.
If testosterone deficiency occurs during puberty, a boy’s growth may slow and no growth spurt will be seen.
The child may have reduced development of pubic hair, growth of the penis and testes, and deepening of the voice.
Around the time of puberty, boys with too little testosterone may also have less than normal strength and endurance, and their arms and legs may continue to grow out of proportion with the rest of their body.
One proposed treatment for low testosterone comes in the form of testosterone supplements.
One type of testosterone supplement, methyl testosterone, has received approval from the United States Food and Drug Administration (FDA).
However, guidelines advise doctors not to prescribe this supplement due to the speed with which the liver metabolizes testosterone.
This can lead to liver toxicity.
While doctors can legally prescribe the supplement, they generally try to avoid this.
Until stronger evidence is available to support the benefits and safety of testosterone supplementation, only older adults with severe clinical symptoms of low testosterone should be candidates for these supplements.
Testosterone replacement therapy
Testosterone replacement therapy (TRT) can help restore some affected functions of low testosterone.
Studies have shown that TRT mainly impacts bone strength and hemoglobin levels in the blood, but not mental sharpness.
The treatment can be administered by:
Skin gels and patches
Tablets that are absorbed through the gums
These can, however, trigger side effects, including:
Increased red blood cell count
Prostate and breast enlargement
In rare cases, breathing difficulties during sleep
Increased risk of cardiovascular disease, although this is subject to debate