Testosterone

What is testosterone?

Testosterone is a sex hormone (androgen) produced mainly by the gonads. The gonads are sex organs, which, in males, are the testicles. The body also produces a hormone called dehydroepiandrosterone (DHEA), in the adrenal glands, which is transformed into testosterone. Testosterone stimulates the development of male characteristics.

Testosterone that our body makes is an anabolic-androgenic steroid. This means muscle building (anabolic), and male sex characteristics (androgenic). Testosterone can be made (synthetic testosterone) to treat various medical conditions.

What is the role of testosterone in the body?

Testosterone performs different roles at different stages of life:

Fetal development

At about seven weeks into pregnancy, a gene on the Y chromosome of male babies begins the development of testicles, which produce testosterone. This then triggers development of internal and external male reproductive organs.

Puberty

Testosterone causes many changes during puberty, including:

• Increased height
• Body and pubic hair
• Growth of the penis, testes and prostate
• Increased libido.

Adulthood

Testosterone in male adults is responsible for:

• The production of sperm
• Telling the body to create new red blood cells

• Ensuring muscles and bones stay strong
• Enhancing libido
• Enhancing feelings of well-being.

Testosterone levels in the blood are controlled by the hypothalamus and pituitary gland. The hypothalamus produces a hormone called gonadotropin-releasing hormone which tells the pituitary gland to release a hormone called luteinizing hormone (LH). When LH reaches the testis, it causes the production of testosterone.

When testosterone levels in the blood increase, gonadotropin-releasing hormone is suppressed, helping to maintain normal testosterone levels.

Any problems with the gonads, hypothalamus, or pituitary gland can cause abnormal levels of testosterone.

How are testosterone levels measured?

One or more of the following tests may be ordered to check testosterone levels:

• Total testosterone blood test
• Luteinizing hormone (LH) blood test
• Follicle-stimulating hormone (FSH) blood test

Testosterone levels are measured in nanograms per deciliter (ng/dL). Normal testosterone levels in males are:

• Under 1 year: <12 ng/dL
• 1 - 5 years: <12 ng/dL
• 6 - 10 years: <25 ng/dL
• 11 - 15 years: <830 ng/dL
• 16 - 17 years: 102 - 1010 ng/dL
• 18 years plus: 193 - 824 ng/dL

What happens if levels of testosterone are too low?

A low testosterone level is called hypogonadism, and there are two main types:

Classical hypogonadism: When testosterone levels are low because of an underlying health condition or damage to the hypothalamus, testicles, or pituitary gland.

Late-onset hypogonadism: When testosterone levels decline due to ageing or an age-related condition, such as type 2 diabetes.

What are low testosterone symptoms?

Low testosterone during puberty can cause slow growth in height and strength, limited development of pubic hair, the voice doesn’t deepen, and reduced growth of male sex organs.

In adults, low testosterone can cause reduced muscle mass, loss of body hair, erectile dysfunction, low libido, and depressed mood.

Always see a doctor if you have any symptoms of low testosterone.