Testosterone is an androgen produced by the adrenal cortex, testes (male at birth), and ovaries (female at birth). It is generally thought to be related to the primary sex hormone assigned to males at birth. Testosterone stimulates the development of male-related secondary sex characteristics (such as body hair and muscle growth) and is essential for sperm production. In those who were designated female at birth, testosterone, among other things, helps maintain the health of the bones and reproductive system, and helps with libido.
Compared to healthy men who were assigned to women at birth, healthy-assigned men who went through puberty had 15 times the testosterone levels assigned to women.
Testosterone imbalance can lead to infertility in any gender. Low testosterone levels in cisgender men can lead to infertility. High testosterone levels are associated with infertility in people who can conceive.
Testosterone levels can be assessed with blood tests. This is usually part of an infertility test for all genders.
Testosterone is a potent steroid hormone chemically formulated as C19-H28-O2. Testosterone is also known as 17-beta-hydroxy-4-androstene-3-one.
Prescription testosterone for the treatment of hypogonadism-related disorders in cisgender men and delayed puberty in cisgender boys.
While it may be used off-label to treat perimenopausal symptoms or low libido, there is no Food and Drug Administration (FDA)-approved indication for the use of testosterone in those women who were designated at birth.
Another area of medicine where testosterone is used is for the trans-male population (those who are designated female at birth but exist as males).
It is available as a gel, topical solution, patch or pill (implanted), or as an injection or oral capsule.
Brand names include Androderm, AndroGel, AndroGel Pump, Aveed, Axiron, Depo-Testosterone, First-Testosterone, First-Testosterone MC, Fortesta, Natesto, Striant, Testim, Testopel, Vogelxo and Vogelxo Pump.
Too much testosterone can cause infertility in any gender. Testosterone supplementation also increases the risk of stroke, high blood pressure, red blood cell buildup, heart attack, blood clots in the legs, pulmonary embolism, and cancer. It is only approved by the FDA for hypogonadism and is not recommended for low testosterone use due to aging. On the other hand, the Endocrine Society supports its use in older men confirming testosterone deficiency to achieve lower-than-normal levels of the hormone, but only if the risks and benefits are carefully scrutinized.
Warning: Do not attempt to supplement testosterone yourself. There are many websites selling “testosterone supplements,” many of which are fake and even dangerous. Even if testosterone supplementation is real, it is not harmless and can worsen or cause infertility of any gender.
If you are checking your testosterone levels, a blood test may be scheduled in the morning.
Two types of testosterone are found in your blood:
- Free testosterone (also called free T) is testosterone that is not chemically bound to anything else.
- Conjugated testosterone accounts for the majority of total testosterone levels. About 98% of testosterone in the blood is bound to one of two proteins: albumin or sex hormone binding globulin (SHBG).
When you test your testosterone levels, your doctor looks at both your free and total testosterone levels.
Your total testosterone level includes free and conjugated testosterone.
Total testosterone levels vary throughout the day. In cis-males under the age of 45, levels were highest in the morning and lower in the evening. Once you’re over 45, it doesn’t matter what time of day you check your level.
The normal range of testosterone depends in part on the interpretation of the laboratory and doctor. Having said that, here are some common values.
For designated males 19 years of age or older:
- Total testosterone should be between 270-1070-950 nanograms per deciliter (ng/dL).
- Free testosterone should be between 50-210 pg/dL picograms per deciliter (pg/dL).
For designated women 19 years of age or older:
- Total testosterone should be between 15-70 ng/dL.
- Free testosterone should be between 1.0-8.5 pg/dL.
Sperm development: Testosterone is essential for the production of sperm in the testes. However, it’s a delicate balance. Both too little and too much testosterone can lead to lower sperm counts.
Associated with so-called secondary male characteristics: this includes growth of facial and body hair, deepening of the voice, increased muscle mass, increased bone size, and distribution of body fat.
Testosterone levels in infants were similar. It is only during puberty that cisgender boys begin to produce significantly higher levels of testosterone, leading to the development of male-related secondary sexual characteristics.
Those women born with abnormally high testosterone levels may experience problems with facial hair, male pattern baldness, and infertility. High testosterone levels are also associated with acne of any gender.
Essential for the development of eggs in the ovary: Androgens play an important role in ovarian follicle development and estrogen production.
Libido (sexual desire): The link between testosterone and libido is well known. Higher levels of testosterone lead to higher levels of libido.
Build Muscle Mass: Cisgender men are more likely to develop muscle mass than cisgender women because they have higher testosterone levels.
Pain tolerance: Testosterone can help people regulate pain levels.
Learning and memory, especially spatial intelligence: Testosterone aids in learning and memory. It is particularly relevant to spatial intelligence.
Cis-males with abnormally low testosterone levels are at risk for learning disabilities.
Cognitive Empathy: Cognitive empathy involves being able to read the emotions of others through body language and facial expressions.
Higher testosterone levels are associated with a reduced ability to read in people.
However, a new study published by the University of Toronto in September 2019 found that giving men testosterone did not reduce their empathy.
Diseases and disorders that affect testosterone levels
When testosterone levels are abnormally low or high, it can affect an individual’s overall health and well-being. This applies to all genders. What can cause abnormal testosterone levels?
In cis men, possible causes of low testosterone include:
- Age (over 50 years old)
- underweight or overweight
- Congenital or chromosomal disorders, such as Klinefelter syndrome (XXY) or Kallmann syndrome
- Pituitary gland problems
- Diseases involving the testes
- Unusually high levels of iron
- Chemotherapy and other cancer treatments
- critical illness or surgery
- some drugs and recreational drugs
- extremely high stress levels
Possible causes of abnormally high testosterone levels in cis men include:
- adrenal or testicular tumor
- Anabolic steroid abuse
- Testosterone Supplements
- physical contact with someone using topical testosterone supplements
In cis women, possible causes of high testosterone include:
- Polycystic Ovary Syndrome (PCOS)
- Congenital Adrenal Hyperplasia (CAH)
- adrenal or ovarian tumor
- Anabolic steroid abuse
In cis-women, the most common cause of low testosterone is menopause.
Testosterone is an essential hormone for everyone. If your levels are abnormal, your doctor may order more tests to investigate the cause. For those with low levels due to the normal effects of aging, testosterone supplementation may be considered.