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Key Hormones – Testosterone

Hadyn Luke posted this on Friday 1st of September 2017 Hadyn Luke 01/09/2017

Tags: Anatomy and physiology

CMS Fitness Courses- Key Hormones - Testosterone

Our blog on Key Hormones offered an overview of five hormones: insulin, glucagon, testosterone, oestrogen and human growth hormone (HGH).

Today we’re looking at testosterone, which belongs to a class of steroid hormones known as androgens and is best known for its role in the development of male characteristics.

Where is testosterone produced?

The key male sex hormone, testosterone is produced primarily by the Leydig cells, interstitial tissue in the testes, when stimulated by lutenizing hormone.

Women’s ovaries also secrete testosterone, but at a much lower level.

In both men and women, testosterone is also produced by the adrenal glands, but only in small quantities.

What functions does testosterone regulate?

In men, testosterone is important for:

  • The development of reproductive organs in a foetus
  • Sex drive, including sexual development in puberty
  • The production of sperm
  • The development of muscle and bone mass
  • The distribution of fat
  • The production of red blood cells

In women, it also contributes to sex drive, bone strength and the development and maintenance of muscle mass and strength.

As testosterone is important in muscle development and strength, high or low levels of testosterone in the body can affect the performance of professional sports people and athletes as well as ordinary gym goers.

What happens if you produce too much testosterone?

In men, the production of testosterone is largely governed by the hypothalamus and the pituitary gland (see our blog on The Endocrine System).

While it’s unusual for adult males to produce too much testosterone, boys and girls with excessive testosterone can enter early puberty, experience growth spurts and potentially become infertile.

Adult women may produce too much testosterone as a result of certain conditions, such as polycystic ovarian syndrome or ovarian cancer. High levels of testosterone in women can cause periods to become irregular or stop altogether, along with increased body hair, deeper voices, acne and fluid retention. They can also cause infertility.

And too little?

Testosterone production in men peaks in early adulthood and gradually declines with age, potentially affecting libido, skin appearance, body hair growth and muscle mass.

In some cases, this can provoke a more extreme reaction, for example:

  • Mood swings
  • Increased weight
  • Loss of muscle tone
  • Osteoporosis
  • Serious problems with sexual function
  • Memory loss and difficulty concentrating

Women can also be affected by a drop in testosterone, particularly post-menopause. This can affect libido, mood, energy levels and muscle strength.

What about anabolic steroids?

Athletes or body builders who use anabolic steroids can cause their hypothalamus to reduce the amount of luteinising hormone secreted by the pituitary gland, which in turn cuts the amount of natural testosterone being produced.

As well as affecting fertility, sex drive and liver function, over use of anabolic steroids can cause mood swings and other behavioural changes.

Other factors that can affect testosterone levels

Factors that can cause lower testosterone levels include:


If you feel you may be suffering from too high or too low levels of testosterone, visit your GP. You can also access online tests but there will be a cost for these. 

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