The testes and male sex hormones

The testes, or testicles, as they’re more commonly known, are vital to men’s health and wellbeing. They play an important role in male fertility, as well as supporting muscle mass, libido, and mood.

In this article, we explore the function of the testes, including their role in reproduction, and offer some top tips for keeping your testes healthy.

We cover:

What are the testes and what do they do?

 

The testes are two oval-shaped organs in the male reproductive system. They’re located behind the penis in a pouch of skin called the scrotum. 

The testes have two main functions:

1. Sperm production— the testes make, store, and mature male reproductive cells or sperm. Sperm are made in the seminiferous tubules of the testes, and there are around 700 of these tubes in each testis.
2. Hormone production—as part of the male endocrine system, the testes make hormones that are vital for processes such as the changes in the male body at puberty and sperm production. These hormones are made in the Leydig cells of the testes. 

Which hormones do the testes make?

 

The testes make testosterone and small amounts of a type of oestrogen called oestradiol.

Testosterone can also be converted to oestradiol in the liver and fat tissues by the aromatase enzyme.

Levels of testosterone rise significantly in males at puberty, leading to the development of male sex characteristics.

At puberty, testosterone causes:

• Development of muscle mass

• Enlargement of the penis

• Increase in body and facial hair

• Lowering of the voice

In men, testosterone is also important for: 

• Bone density

• Libido (sex drive) and sexual function 

• Maintaining muscle mass and strength

• Regulating mood

• Sperm production

Testosterone levels usually peak during adolescence and early adulthood. After that, they naturally decline by about 1% each year from around the age of 30 [1]. Some studies have shown that the decline is even slower than this, especially before the age of 60 [2]. 

What can affect testosterone levels?

 

Low testosterone is much more common than (naturally) high testosterone levels, and there are many reasons why your levels may be on the low side. These can include lifestyle factors such as chronic stress and lack of sleep.

However, persistently low testosterone levels may indicate hypogonadism (or testosterone deficiency). Hypogonadism is normally diagnosed by a hormone blood test and related symptoms, such as reduced sex drive and low mood. 

Causes of hypogonadism include:

• Ageing—testosterone levels naturally decline as men get older. However, ageing can cause levels to dip abnormally low, leading to late-onset hypogonadism.

• Damage to the testes e.g. through surgery, trauma, or treatments such as chemotherapy.

• Genetic and developmental disorders, such as Klinefelter Syndrome—an inherited condition where a male is born with an extra copy of the X chromosome. Undescended testicles can also cause testosterone deficiency. This is a common childhood condition, where the testes aren’t in their usual place in the scrotum.

• Medication or anabolic steroid use, which can signal the body to reduce its natural production of testosterone.

• Other health conditions—low testosterone levels are associated with other medical conditions such as diabetes and liver disease, as well as infections that can affect the testes like mumps.

What are the symptoms of low testosterone in men?

Symptoms of low testosterone in men include:

• Difficulty sleeping

• Erectile dysfunction

• Infertility

• Low energy

• Low libido

• Low mood and motivation

• Reduced muscle mass and difficulty gaining muscle 

• Small testicles

Can I increase my testosterone level naturally?

It’s well known that lifestyle factors, such as drinking too much alcohol and lack of sleep can affect testosterone levels [3,4]. Therefore, it may be possible to increase your testosterone naturally with healthy changes.

Lifestyle changes that may improve testosterone levels include:

• Drinking less alcohol

• Getting plenty of good-quality sleep

• Keeping active and exercising regularly

• Managing stress

For some men with diagnosed hypogonadism, testosterone replacement therapy (TRT) may be recommended.

Why do men need oestradiol?

 

In men, oestradiol plays a role in:

• Sex drive (libido)

• Getting an erection

• Cognition and brain function

• Maintaining strong, healthy bones

• Sperm production

What are the symptoms of high oestradiol in men?

The symptoms of excess oestradiol in men can vary, but some of the main symptoms you may experience include:

• Growth of excess fatty breast tissue (gynecomastia)

• Infertility—although oestradiol is important for sperm production, excess levels can disrupt this process

• Reduced sex drive and erectile dysfunction (ED)

What causes high oestradiol levels in men?

Causes of high oestradiol in men include: 

• Ageing—as men get older, testosterone levels naturally decline while oestrogen levels increase.

• Exposure to exogenous (environmental) oestrogens—sources of exogenous oestrogens include plastics such as BPA. Research is ongoing but suggests that exposure to exogenous oestrogens can increase oestrogen levels within the body (endogenous levels), which can impact male fertility [5]. 

• High testosterone levels—taking too much TRT or steroid misuse can cause a sudden increase in testosterone. This can lead to an increase in the aromatase enzyme, which may boost oestradiol levels. 

• Body composition—the majority of aromatase is made by the fat cells. So, the more fat cells you have, the higher your chance of raised aromatase and oestradiol.

How is high oestradiol treated in men?

You may be able to naturally reduce high oestradiol levels by making healthy changes. Losing weight if you’re overweight and managing stress can be effective. These actions can also help keep your testosterone levels within the normal range.

If diet and lifestyle changes aren’t enough to reduce raised oestrogen levels, reach out to your GP to explore the causes and treatment options. Sometimes, doctors prescribe aromatase inhibitors that lower the amount of testosterone converted to oestradiol.

Five top tips for healthy testes

 

There are many steps you can take to protect your testicular health—here are our five top tips:

1. Examine your testicles regularly—regular self-checks help you understand what’s normal for you, making it easier to spot any changes. Lumps or swellings are common and can be caused by several conditions. While these changes rarely indicate testicular cancer, it’s important to get them, or any other changes, checked by a GP. The NHS recommends a self-exam every month and provides guidance on how to check your testicles.
2. Keep them cool—the testicles are located outside the body as the best temperature for sperm production is a few degrees lower than body temperature (34 degrees to be precise).
   So, avoid situations that could raise their temperature for long periods.
   
   To keep your testicles cool: 
     -  Avoid wearing tight trousers or jeans
     -  Don’t sit with your laptop directly on your lap for too long 
     -  Limit the length of time you stay in hot baths 
    
3. Watch your weight—obesity is linked to lower sperm count and quality [6]. Maintaining a healthy weight can help protect your testicular function and fertility. 
4. Practise safe sex—some STIs may not show any symptoms, so you may not know you have one for weeks or even years. If left untreated, these infections can affect your testicles and potentially cause fertility problems. Using protection during sex is the best way to protect yourself from STIs. 
5. Wear protection when playing sports—there are many options for protecting yourself, whether you play cricket, rugby, football, or another contact sport.

How to check your testosterone level

 

If you’re experiencing symptoms or just want to check your testosterone level is normal for your age, try our at-home Testosterone Blood Test. 

You can also take our Male Hormone Blood Test in the comfort of your home, using a finger-prick test kit. This test gives you a more in-depth look at your hormone health, including testosterone and other hormones that could be affecting your sex drive, muscle mass, mood, and energy levels.

For more help on choosing a test, check out our Male Hormone Blood Test Buying Guide. You can find more information and advice in our Hormone Health Hub.

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References

1. Tajar, A., et al. (2010) Characteristics of secondary, primary, and compensated hypogonadism in aging men: evidence from the European Male Ageing Study. J Clin Endocrinol Metab. 95(4):1810-8. doi: 10.1210/jc.2009-1796. Epub 2010 Feb 19. PMID: 20173018.
2. Handelsman, D.J., Yeap, B., Flicker, L., Martin, S., Wittert, G.A., and Ly, L.P. (2015) Age-specific population centiles for androgen status in men. Eur J Endocrinol, 173(6):809-17. doi: 10.1530/EJE-15-0380. Epub 2015 Sep 18. PMID: 26385186.
3. Rachdaoui, N. and Sarkar, D.K. (2017) Pathophysiology of the Effects of Alcohol Abuse on the Endocrine System. Alcohol Res, 38(2):255-276. PMID: 28988577; PMCID: PMC5513689.
4. Leproult, R. and Van Cauter, E. (2011) Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 305(21):2173-4. doi: 10.1001/jama.2011.710. PMID: 21632481; PMCID: PMC4445839.
5. Santiago, J., Silva, J.V., Santos, M.A.S., and Fardilha, M. (2021) Fighting Bisphenol A-Induced Male Infertility: The Power of Antioxidants. Antioxidants (Basel), 10(2):289. doi: 10.3390/antiox10020289. PMID: 33671960; PMCID: PMC7919053.
6. Hammiche, F., Laven, J.S., Twigt, J.M., Boellaard, W.P., Steegers, E.A., and Steegers-Theunissen, R.P. (2012) Body mass index and central adiposity are associated with sperm quality in men of subfertile couples. Hum Reprod, 27(8):2365-72. doi: 10.1093/humrep/des177. Epub 2012 Jun 12. PMID: 22693175.