What is testosterone?
Testosterone is the primary sex hormone in males, but it is also important in females. Testosterone is mainly secreted from the testes in males, and from the ovaries in females.
What does testosterone do in males?
Although males have much higher levels of testosterone than females, this androgen plays an important role during the life cycle of both genders. In this article, we focus on the role of testosterone in males.
Before birth, testosterone levels are associated with sex formation, with higher levels initiating the development of male reproductive organs. During puberty, testosterone plays a role in many of the typical changes that occur as boys grow into men. This includes increases in body and pubic hair, enlargement of the penis, testes, and prostate gland, deepening of the voice, teenage acne, and remodeling of the facial bones (1,2).
Other roles of testosterone include:
- Increasing libido (sex drive)
- Controlling fat distribution
- Enhancing muscle and bone growth
- Normal sperm production
- Red blood cell production
How are testosterone levels controlled?
Testosterone levels can fluctuate slightly each day, with higher levels in the morning. However, strict control helps to maintain blood testosterone at normal levels. The hypothalamus in the brain releases gonadotrophin-releasing hormone (GnRH), which signals the pituitary gland (also in the brain) to produce luteinizing hormone (LH). LH travels through the blood to the testes to stimulate the synthesis and release of testosterone (1).
As the hypothalamus detects increasing levels of testosterone in the blood, it suppresses the production of GnRH, so in turn, there is less LH released, so less stimulation of testosterone production. This control system is known as negative feedback. As testosterone levels drop, the hypothalamus increases the production of GnRH, therefore more LH is produced, and testosterone synthesis is stimulated once again (1).
What are the symptoms of high testosterone in males?
In male children, elevated testosterone may cause a false growth spurt and early puberty (precocious puberty). This can contribute to infertility issues later in life.
Naturally elevated testosterone in adult males is rare and is not likely to cause any noticeable symptoms. However, males who take anabolic steroids (synthetic substances similar to testosterone) actually end up with lower levels of their naturally produced testosterone (3). Long-term use of anabolic steroids can result in:
- Low sperm counts
- Decreased sex drive
- Smaller testes
- Breast development
- Liver disease
- Behavioural changes
- Weight gain
- Damage to heart tissue
- Excessive body hair
What are the symptoms of low testosterone in males?
Low testosterone has differing effects depending on the age of the individual. Testosterone deficiency during fetal development can cause the incomplete development of male characteristics, while deficiency at puberty can slow growth and reduce the development of pubic hair, deeper voice, and penis and testes growth (1,4).
In adult males, testosterone levels naturally decline with age, and this can sometimes be called male menopause (or andropause) (1). However, unnaturally low testosterone can result in:
- Reduced muscle tone and increased body fat
- Loss of body hair
- Weight gain
- Reduced sex drive and performance
- Memory loss
- Sleeping issues.
- Increased risk of osteoporosis
1. You and your Hormones, an education resource from the Society of Endocrinology. Reviewed May 2021.
2. Raggatt LJ, & Partridge NC. (2010). Cellular and molecular mechanisms of bone remodeling. J Biol Chem, 285 (33), 25103-25108.
3. Testosterone – What It Does And Doesn’t Do. (2019). Harvard Health Publishing, Harvard Medical School.
4. What is Low Testosterone? Urology Care Foundation.