Most men associate testosterone with key changes that begin during adolescence. But what is this hormone, and why does it play such an important role in daily life?

As the primary androgen responsible for male traits, it’s common to single out this hormone’s role in the changes that occur during puberty - such as growth spurts, deepening of the voice, facial hair growth, and genital development.

More accurately, however, testosterone's influence goes beyond just male development. It is essential for growth from teenage years into adulthood, and is also crucial for several important functions in female biology.

In this guide, TRT specialist Dr. Jeff Foster breaks down common questions about testosterone and explains why this hormone is so important for many essential functions in the body.

What is Testosterone?

Testosterone is the main male sex hormone. This means it is responsible for the development and maintenance of physical and sexual characteristics such as the prominence of the Adam's apple, increased muscle mass, libido, and sperm production.

In men, this hormone is produced in the testicles, or more accurately - Leydig cells found within them.

For women, the ovaries take time out of oestrogen production, to create small amounts of testosterone needed to support core aspects of female health like libido and muscle mass.

Additionally, the adrenal glands in both sexes contribute to testosterone production.

Similar to oestrogen and anti-inflammatory hormones like cortisol, testosterone functions as a steroid hormone, this means it supports multiple systems in the body from the immune system to the reproductive system.

What Does Testosterone Do for Men?

Think of testosterone as the body’s natural regulator, guiding it through the various stages of growth and development. This is particularly true during puberty - where testosterone production in males increases by 20-30 times.

During this period, the hormone drives major physical changes that mark the transition into adolescence - like the growth of a moustache, the development of pubic hair, and rapid growth spurts.

These changes are credited to testosterone’s role in guiding the body into the next phase of maturation.

Outside of puberty, testosterone continues to be influential throughout adulthood, helping to maintain sex drive and function. Its impact extends beyond physical health, supporting cognitive function and emotional well-being.

This hormone’s effects reach nearly every cell in the body, impacting overall health and wellbeing.

Importance of Testosterone

Because testosterone has a role to play across a majority of the body's cells and functions - this hormone is instrumental in maintaining overall wellbeing.

Should the body's supply of testosterone drop to low levels, this leads to a state of hypogonadism or low-t. This condition can lead to various effects, from metabolic changes, reduced libido, and erectile dysfunction, to more subtle symptoms such as fatigue, low mood, brain fog, lack of motivation, and a general sense of aging and weariness.

A common occurrence, hypogonadism is estimated to affect around 40% of men older than 45 and 50% of men in their 80s.

To further underscore the importance of this hormone - having low testosterone levels can affect the cardiovascular system and bone density, while also increasing the risk of diabetes.

What Causes Testosterone Levels to Change?

Age is the main factor driving the natural decline in testosterone with adults commonly experiencing a 1% drop in testosterone levels each year. Other major contributors to low testosterone include obesity and diabetes.

In a survey of 3,369 men aged 40 to 79 from various European centers, researchers found that obese participants were more likely to exhibit signs of secondary hypogonadism, where low testosterone levels result from changes in the brain rather than issues with the testes.

Likewise, type 2 diabetes is so commonly associated with low serum testosterone, the Endocrine Society recommends morning testosterone measurement when diabetic patients begin to show signs of unexplained weight loss, sexual dysfunction, plus weakness or mobility limitation.

Serious medical conditions like testicular cancer or mumps can also lead to reduced testosterone levels. In some cases, less-known factors like asthma, depression medicines, antifungal treatments, some painkillers, or even lifestyle factors like poor sleep and diet can influence reduced testosterone levels.

Symptoms of Low Testosterone

Low testosterone can manifest in three main areas - although men may sometimes experience low-t symptoms in just one aspect.

Physically, it's common to observe the following:

• A drop in energy, motivation
• Fat gain
• Losing strength

Men with low testosterone have also complained of weight and size plateaus despite years in the gym.

Mentally, low testosterone can cause:

• Brain fog
• Trouble focusing
• Lack of enthusiasm for daily life

Some of these feelings often mirror apathy, with men no longer finding joy in things they once loved. Low testosterone can cause depression, anxiety, or a dip in confidence.

Testosterone levels can also impact sexual life, with men reporting:

• A loss of libido
• Trouble with erections
• A general lack of interest in sex altogether

What is a Normal Testosterone Level?

Ideally, this should be a straightforward question, but like many evolving areas of medicine, answers may vary depending on who's asked. The British Society of Sexual Medicine, which has developed national guidelines for testosterone therapy in the UK, recommends that most men aim for testosterone levels between 15-30 nmol/L, regardless of age. In the NHS, however, 'normal' ranges can change depending on your house address, leaving healthy t-levels at the mercy of your chosen postcode!

Difference Between Free and Total Testosterone

When determining testosterone concentration, it's important to differentiate between free and total testosterone levels. We’ll explain why.

As the body produces testosterone, it's often assumed that the hormone simply circulates through the bloodstream, reaching target tissues or organs where it binds to receptors to regulate key functions like muscle growth and mood. However, the process is more complex—testosterone must first be present in the right forms and amounts to effectively interact with these receptors and perform its essential roles. In fact, not all produced testosterone is readily available for use.

Only about 3% of total testosterone is considered 'free,' meaning it's unbound and able to attach to androgen receptors for biological activity. The majority of testosterone binds to other substances, such as sex hormone-binding globulin (SHBG), which limits how much is freely available for use.

The amount of testosterone left after taking out the bound testosterone, is the free testosterone which more accurately depicts the bioavailable amounts of this hormone in the blood.

It's important for men to know their free testosterone concentration. This is especially useful where patients have symptoms of low testosterone, but readings show near-normal or borderline normal testosterone levels.

Why Should You Check Your Testosterone Levels?

Dealing with low testosterone can be unpredictable, as symptoms often appear in different, sometimes unclear ways.

Many men will often mistake the tiredness, lethargy, or sudden weight changes as typical of the ageing process. In reality, these are signs the body is running low on the male hormone, and not a manifestation of poor self-care habits.

With nearly 25% of the male population affected by low testosterone, it's important to schedule regular checks to identify if symptoms indicate a hormone deficiency.

How Can I Check if I Have Low Testosterone?

The most accurate way to measure testosterone levels is through a TRT morning blood test. This timing is crucial because testosterone concentration is typically highest between 7 a.m. and 12 p.m., providing a clearer snapshot of the body’s natural production. Testing later in the day may reflect lower levels, which could lead to an incorrect low testosterone diagnosis. However, for patients already on testosterone replacement therapy (TRT), testing can be done at any time of day.

Thanks to modern advancements, convenient finger-prick testing kits now allow these tests to be carried out easily from the comfort of home.

What is the Treatment for Low Testosterone?

The first step in treating low testosterone is to source the cause of this deficiency. In some cases for example, thyroid disease or even being underweight could result in low testosterone levels. In these situations, simply addressing the cause can improve the effects of low testosterone levels.

However, in most cases where there is no obvious cause for the decline, TRT can effectively replace what’s missing from the body.

Treatment options include topical gels or creams, as well as injections delivered at different intervals, depending on the patient’s needs.

What if I Don’t Treat Low Testosterone?

In the short term, there may not be any immediate, lasting consequences of not managing low testosterone levels. In fact, some people may go years without addressing the hormone deficiency.

The major challenge is that during this time, you may experience symptoms that negatively impact your quality of life. Low mood, depression, poor memory, and brain fog could serve as unwanted reminders that your body’s hormones are out of sync.

More concerning is that low testosterone is linked to serious health risks, including metabolic disease, obesity, type 2 diabetes, bone thinning, cardiovascular disease, and even dementia.

Conclusion

To conclude, testosterone plays a critical role in various aspects of male health, from physical performance to mental well-being. Understanding its functions, potential imbalances, and the options available for managing low levels, such as lifestyle changes or testosterone replacement therapy, can help men make informed decisions. Whether seeking to enhance vitality or address health concerns, it's important to consult with a healthcare professional to determine the best course of action for maintaining optimal testosterone levels.