What is testosterone?
Understand what testosterone does, how to measure it, and how to keep your levels in check.
Testosterone (T) is perhaps one of the best-known sex hormones. Often associated with masculinity, its effects go far beyond just muscle mass and libido. It plays a crucial role in both men's and women’s health, regulating libido, muscle mass, and energy levels.
In this article, we explore the functions of testosterone, and why monitoring T levels can support overall health.
- What is testosterone?
- Six main functions of testosterone
- Monitoring testosterone levels
- Bone mass
- Mood and energy levels
- Muscle growth and development
- Red blood cell production
- Sex drive (libido)
- Reproductive tissue: Testosterone is vital for developing the testes and prostate. It also plays a role producing sperm.
- Muscle mass and strength: Higher levels are associated with increased muscle strength and physical performance.
- Bone density: Low levels can lead to decreased bone density, increasing the risk of osteoporosis and fractures.
- Libido and sexual function: Testosterone influences sexual desire and function in men and women. It plays a role in regulating libido, erectile function, and sperm production[1].
- Mood regulation: Low levels have been associated with symptoms of depression, irritability, and fatigue[2].
- Cognitive function: Testosterone may play a role in memory and spatial abilities. However, more research is needed to fully understand this[3].
- Age: From the 30s onwards, levels decline naturally in men.
- Underlying medical conditions: Being obese or diabetic is likely to cause a decline.
- Medications: Prescription medications like spironolactone (used to treat high blood pressure and heart failure), opioids (painkillers), and statins (lipid-lowering therapy) may cause a decrease.
- Decreased libido
- Shrinkage of the testicles
- Erectile dysfunction
- Diabetes
- Liver failure
- Obesity
- Difficulty maintaining muscle mass
- Erectile dysfunction
- Fatigue
- Low libido
- Mood disturbances
- Smith LB, Walker WH. The regulation of spermatogenesis by androgens. Semin Cell Dev Biol. 2014 Jun;30:2-13. doi: 10.1016/j.semcdb.2014.02.012. Epub 2014 Mar 2. PMID: 24598768; PMCID: PMC4043871.
- Johnson JM, Nachtigall LB, Stern TA. The effect of testosterone levels on mood in men: a review. Psychosomatics. 2013 Nov-Dec;54(6):509-14. doi: 10.1016/j.psym.2013.06.018. Epub 2013 Sep 7. PMID: 24016385.
- Beauchet O. Testosterone and cognitive function: current clinical evidence of a relationship. Eur J Endocrinol. 2006 Dec;155(6):773-81. doi: 10.1530/eje.1.02306. PMID: 17132744.
- North Bristol NHS Trust. n.d. Testosterone | North Bristol NHS Trust. [online]
- North Bristol NHS Trust. n.d. Free Testosterone | North Bristol NHS Trust. [online]
What is testosterone?
Testosterone is a sex hormone that belongs to a class of hormones known as androgens. Both men and women testosterone, but concentrations are naturally much higher in men.
Where is testosterone produced?
The testes and the ovaries primarily produce testosterone. It’s also produces in much smaller amounts in the adrenal glands (which are located above the kidneys). It’s then the responsibility of the hypothalamus and pituitary gland to regulate levels within a normal range.
You may know that testosterone is responsible for changes during puberty, such as voice deepening, body hair growth, and growth spurts. But it does much more than that.
In adults, testosterone plays an important role in regulating:
Total T vs free T: what’s the difference?
Testosterone is secreted directly into the bloodstream from the testes. Most of it binds to two proteins: sex hormone-binding globulin (SHBG) and albumin.
The remaining testosterone that isn’t attached to proteins is known as free testosterone (FT), the more active form of the hormone. FT enters the cells and binds to receptors where it triggers changes in growth and metabolism.
Total testosterone (TT) is a measure of how much testosterone there is in the blood — both free and bound. Therefore, TT will always be higher than FT.
Generally, if a deficiency is suspected, a TT measurement is taken first. If this is at the low end of the normal range, an FT measurement may be taken too. That’s because it’s possible to have a normal TT with a low FT level.
Six main functions of testosterone
Testosterone is important for:
Monitoring testosterone levels
You can check your levels at home with a Testosterone Blood Test. For a more comprehensive check of your hormones, we recommend our Male Hormone Test.
Testosterone levels are highest in the morning and gradually decline throughout the day. Therefore, it’s best to take your sample in the morning (ideally 7 – 10 am). If your result is borderline or abnormal, you may be asked to repeat your test.
What is a normal testosterone level?
Both men and women need the right amount of testosterone to develop and function normally.
Levels may differ depending on:
Because levels vary, it can be difficult to quote a normal range that covers everyone. For a typical man, the normal range is approximately 8.7 – 29 nmol/L for total testosterone[1], and 0.2 – 0.62 nmol/L for free testosterone[2].
What do raised levels mean?
Men are unlikely to develop raised levels of testosterone naturally. However, this can happen so it’s best to seek medical advice if your levels are high and there is no obvious cause.
Elevated levels are more commonly seen in people who take testosterone-boosting supplements, for example, anabolic steroids or testosterone replacement therapy (TRT).
Abusing anabolic steroids decreases the amount of testosterone the body naturally produces, as it assumes the body is producing enough.
Anabolic steroid use can cause side effects such as:
What could low levels mean?
In men, it is normal for testosterone levels to gradually decline with age. But for some men, the decline can lead to a deficiency.
Certain health conditions may also put men at risk of developing a deficiency, including [3]:
Symptoms and blood test results need to be considered to diagnose a deficiency.
Symptoms suggestive of deficiency include:
Best blood tests for testosterone
Regular testing and consultation with a healthcare professional can provide valuable insights and guidance. So, whether you are curious about your hormonal health or want to address specific symptoms, a blood test could help.
Best for a quick check: Testosterone Blood Test
Best for men's hormones: Male Hormone Blood Test
Best for a comprehensive health check: Advanced Well Man Test
