Testosterone

Take-home points

• Testosterone is an important hormone that is naturally produced by both men and women.
• Too much or too little can cause health problems that may be difficult to diagnose. Testosterone deficiencies can affect physical, mental and sexual health.
• Testosterone levels can be assessed using a simple blood test. Testosterone level tests can be carried out at the doctor’s office or in the comfort of your own home.
• Testosterone replacement therapy is a convenient and cost-effective treatment that can alleviate symptoms related to low testosterone.

What is testosterone?

Hormones act as chemical messengers, sending signals from the brain to the parts of the body so that an action or function can take place. Testosterone is a natural hormone produced by both men and women and is involved in regulating a number of functions within the human body.^1,2 In men, testosterone is primarily produced in the testicles, while smaller quantities are also produced by the adrenal glands. In women, testosterone is produced in various locations: a quarter of which is produced in the ovaries, a quarter in the adrenal gland, and a half in the surrounding tissues of the ovaries and adrenal gland.³

Role of testosterone in the body

Despite being known primarily for its role as a ‘sex’ hormone, testosterone has been shown to carry out various important roles within the body, from regulating your sex drive to influencing muscle growth.⁴

Testosterone in men

In men, testosterone is responsible for producing and regulating masculine characteristics. It has a vital role to play during puberty and as adults, it has a crucial role with regard to fertility, muscular development and metabolism.¹ Testosterone levels are likely to gradually decline by approximately 1-2 % per year after age 30.⁵ Consequently, as men age their testicles may become smaller, their sex drive may take a hit, and some of the mechanisms regulating aspects of their body may decline, putting them at risk for further complications.² Learn more about the role of ageing on testosterone levels.

Testosterone in women

Testosterone levels are approximately ten times lower in women than they are in men. In women, testosterone is an important component of female sexuality. It regulates sexual desires and is also associated with greater well-being, reduced anxiety, and fewer flare-ups of depression.⁶ Concentrations of testosterone first begin to increase in girls at around the age of 6–8 years, whilst natural testosterone levels tend to decline when a woman reaches 40.⁶ The reason for this decline is not known, and opinions are mixed as to whether or not it is related to menopause, with hypotheses suggesting a “warning” role played by the ovaries and adrenal gland.⁶  

What is a normal level of testosterone?

Men and women have different “normal” levels of testosterone.¹ Men naturally have higher levels than women, but fluctuations in levels can occur even within the same sex. The majority of testosterone in the human body is attached to proteins; however, some testosterone may float freely in the body. This means that testosterone can be measured by different blood tests, each of which will have its own defined range of what normal is:  

• Total testosterone test: a blood test used to measure both free testosterone and the testosterone attached to proteins.⁷  
• Free testosterone test: a blood test that measures only the form of testosterone not attached to proteins.⁸

‍The BSSM guidelines define a normal serum testosterone (total testosterone) level as between 10.4 to 34.7 nanomoles per litre (nmol/L) for adult men.⁹

Read our guide on how to interpret testosterone blood test results

What happens if you have high testosterone?

Problems related to testosterone arise due to either the under or over-production of testosterone, receptor insensitivity (the parts of the body which testosterone attaches to elicit a response), or impaired metabolism of testosterone.¹  High testosterone in men most often occurs after the injection of anabolic steroids.¹⁰ Despite this resulting in increased muscle mass, a higher sex drive, and an arguably more positive outlook on life, the cost at which these benefits come can be detrimental. Men with high testosterone counts resulting from anabolic steroid use may be at a greater risk for the following:¹¹

• Sexual dysfunction
• Cardiovascular complications
• Mood disturbances
• Liver damage

In women, in addition to the above, high testosterone can lead to facial hair growth, polycystic ovary syndrome, metabolic diseases such as type 2 diabetes, and disruptions in ovulation that lead to reduced fertility.^{12, 13}

What happens if you have low testosterone?

Decreased production of testosterone can occur naturally with ageing, certain medications, chemotherapy, and androgen-related disorders.¹⁴ In men, those with low testosterone levels may experience one or more of the following symptoms:

• Erectile dysfunction
• Subfertility
• Gynaecomastia (unwanted breast enlargement)
• Faituge
• Reduced muscle and bone mass

Testosterone replacement Therapy

There are many ways in which a healthcare provider can treat low testosterone. Testosterone replacement therapy, or TRT, has several forms such as testosterone gel, testosterone injections, and testosterone patches, and each can be used depending on individual preference. The overarching aim of TRT is to help alleviate the symptoms associated with testosterone deficiency, thereby promoting greater libido, mood, and bone mass, and in men, providing better erectile function.¹⁵

Learn more about testosterone replacement therapy

A Test You Shouldn’t Skip

The signs of low testosterone aren’t obvious at times, producing symptoms that may be attributed to other conditions. If you are experiencing any symptoms of testosterone deficiency or are worried about the side effects you may experience following the supplementation of testosterone, then it's important to get in touch with your healthcare provider so that the appropriate testosterone tests can be initiated.

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Join the conversation on the TRTed Community! 

References:

1. Jones H. Testosterone Deficiency in Men 2012;9–20.
2. Davis SR, et al. Lancet Diab & Endo 2015;3(12):980–92.
3. Guay A, Davis S. Boston University Medical Campussexual Medicine 2002. Available here.
4. Wein H.  U.S. Department of Health and Human Services 2016. Accessed June 2023. Available here.
5. Jones H. Clinical Interventions in Aging 2008;Volume 3:25–44.
6. Davis S. J Reprod Med 2001:46(3 Suppl);291-6.
7. Guzelce EC, et al. Best Pract Res Clin Endocrinol Metab 2022;36(4):101683.
8. Shea JL, et al. Adv in Clin Chem 2014;59–84. doi:10.1016/b978-0-12-800094-6.00002-9.
9. BSSM. Practical guide on the assessment and management of testosterone 2017. Available here.
10. NHS North Bristol, Testosterone 2023. Available here.
11. Bond P, et al. Frontiers in Endo 2022;13.
12. Van Amsterdam J, et al. Regulatory Toxicology and Pharmacology 2010;57(1):117–23.
13. Patel SM, et al. Journal of Clinical Endocrinology and Metabolism 2009;94(12):4776–84.
14. Watts M. Testosterone and Diabetes 2023. Available here.
15. Cohen J, et al. Frontiers in Endocrinology 2020;10.
16. Huang G, et al. Journal of the American Geriatrics Society 2018;66(11):2172–7.
17. Barbonetti A, et al. Andrology 2020;8(6):1551–66.