How Important is Testosterone, Really?

Written by
The Manual Team
Medically approved by
Dr Earim Chaudry
Last updated
7th January 2022

In 30 seconds…

Testosterone – it’s not all about lifting weights or driving fast cars. In fact, testosterone is one of the body’s essential hormones: a chemical messenger that regulates many important processes.

Because testosterone is an androgen, it helps produce male traits such as a deep voice, body and facial hair, and higher muscle mass. It’s also crucial for your sexual functioning and fertility.

When your testosterone levels get too low, this can cause health problems and impact your quality of life, so you may benefit from medical treatment.

The word “testosterone” is often used synonymously with “manliness” or “masculinity”. But actually, while testosterone does help produce typically male traits like body hair and a deep voice, this little hormone has a much bigger role than that. For example, did you know that testosterone is important for bone density? And that women need testosterone, too?

Read on to find out more about how testosterone works in your body, what can happen if your testosterone levels are too high or too low, and how low testosterone can be treated.

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What is Testosterone?

Testosterone is a hormone – that is, a substance that carries chemical messages around your body through the bloodstream, keeping all the body’s processes ticking over. However, testosterone is a specific kind of hormone called an androgen, which means it’s responsible for the development of male characteristics.

From as early as 7 weeks after conception, testosterone will start to get to work in the body of a male foetus, helping to form the male genitals.

In men, testosterone is produced in the testicles, and to a lesser extent the adrenal gland, as a result of a series of chemical messages sent by the brain via the pituitary gland. The process is closely regulated so that just the right amount of testosterone is produced for your body’s needs.

In women, testosterone is produced in the ovaries and the adrenal gland. Although much less of the hormone is required for women than for men, it’s still crucial for their fertility and bone density.

What Does Testosterone Do for a Man?

Testosterone plays a crucial role in numerous body processes for men, from initial changes in puberty, to sustaining fertility when you’re looking to start a family – to staying fit and healthy into older age.


When puberty hits, the testosterone levels in a boy’s body surge. This brings about the changes associated with male adolescence, including the voice breaking, facial hair and increased body hair, and growing genitals. However, if a boy does not produce enough testosterone at this stage he may not develop these masculine features.

Sex and Fertility

Testosterone is essential for ensuring that a steady supply of mature sperm is produced in the testicles. It also affects your level of sexual desire and functioning, with testosterone sustaining the sex drive and playing a role in healthy erections.

Muscles, Bones, and Fat

When you exercise, testosterone helps to build up muscle mass by encouraging protein synthesis and tissue growth. That’s why testosterone is sometimes taken as a steroid by athletes.

Testosterone also sends a message to the bone marrow, causing it to make more red blood cells, which maintains healthy bone density. In addition, the hormone plays a role in distributing fat across your body and helps you burn fat more efficiently during physical activity.


Testosterone is linked to typically “masculine” behavioural traits, such as dominance, aggression, and competitiveness. However, it’s too simplistic to say that testosterone causes these behaviours: lots of other factors, including personality, culture, and upbringing, contribute to them.

What are the Ideal Testosterone Levels?

The ideal level of testosterone will be different for every man – it’s the amount of the hormone your body needs for healthy functioning. However, levels of 12 nmol/L (nanomoles per litre of blood) or higher are usually considered “normal”. If your testosterone levels become too high or too low you may experience symptoms that impact your quality of life. 

Too High

Abnormally high levels of testosterone are mainly seen in athletes who take the hormone as a steroid. Symptoms include low sperm count, testicle shrinkage, and erectile dysfunction (which is counterintuitive, as low testosterone also impacts sexual functioning); high blood pressure and increased risk of blood clots; weight gain and fluid retention; and mood swings.

Too Low

For some men, their bodies can’t produce enough testosterone to fulfil all the functions we discussed above and they begin to experience health issues. This condition is known as “testosterone deficiency”, “hypogonadism”, or, informally, “Low-T”.

Low-T can be caused by a hormonal disorder, an underlying health condition, or ageing. After the age of 30, your testosterone levels gradually decline by 1–2% per year. However, current research suggests that only about 2% of older men will suffer from diagnosable testosterone deficiency.

Symptoms include loss of sexual desire and erectile dysfunction, low energy and fatigue, decreased muscle mass and bone density, depression and irritability, and loss of body and facial hair.

Should I Consider Testosterone Replacement Therapy?

If you’re concerned that you may have low testosterone levels, a visit to your GP may put your mind at rest. Low-T is diagnosed through a blood test and a consideration of your symptoms. 

The main treatment for low testosterone levels is Testosterone Replacement Therapy. This involves administering extra testosterone to your body, usually via a topical gel, skin patch, or injection.

For men suffering severe symptoms from Low-T, this treatment can have very positive effects and improve their quality of life. But the therapy does have certain associated risks that should be considered before starting treatment – including increased risk of blood clots, cardiovascular disease, and prostate issues.

You may also be committing to treatment for the long-term, if your body can’t make enough testosterone on its own to support all the essential processes the hormone maintains.

Key Takeaways…

So, how important is testosterone? Very important! This hormone plays a role in so many aspects of your health – from adolescent development, to sexual functioning and fertility, to the very structure of your body in its bones and muscles. Look after your testosterone levels, and they’ll look after you.

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

Further reading

From our health centre. Experts, information and hot topics. See all Testosterone articles

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