Testosterone is the primary male sex hormone.
It regulates everything sexual going on in your body. Therefore, to have adequate amounts of testosterone is necessary in order to get erections, to have a strong libido and to avoid struggling with erectile dysfunction.
Testosterone also plays an important role in the development of male characteristics such as muscle mass, bone growth, body hair, and a deeper voice.
It also promotes certain kinds of behavior such as competitiveness, risk-taking, and dominance.
In addition, a normal testosterone level is essential for your overall health and well-being.
Let’s start by understanding the difference between free and bound testosterone.
The Forms Of Testosterone (Free And Bound)
Testosterone belongs to a group of hormones called androgens.
Androgens stimulate and control the development and maintenance of male characteristics and sexual development.
Where is this testosterone (and other androgens) made?
About 95% of the testosterone is made in your testicles. And the rest is made in the adrenal glands that sit on top of your kidneys.
Although testosterone is the primary male sex hormone, women also have it.
But, adult males have about 10x more testosterone than adult females. And as men also use more testosterone than women, the daily production of testosterone is about 20x greater in men.
On average, a healthy man produces about 7 mg of testosterone every day.
However, not all of these 7 mg can immediately be used by your body. Because after being produced, most of the testosterone binds to proteins and therefore becomes inactive.
As a result, the testosterone in your body is found in the following three forms:
- Free testosterone: This is testosterone in its optimal and purest form. The reason it’s called ‘free’ is because it isn’t attached to any proteins. Unbound to proteins, free testosterone can carry out its functions freely by entering cells and activating receptors. Free testosterone normally makes up 1-3% of a your total testosterone.
- SHBG-bound testosterone: About 40-50% of your testosterone is bound to a protein called sex hormone-binding-globulin (SHBG). SHBG binds to testosterone in order to transport it to somewhere in the body where it can be used. It also binds to testosterone as a way of storing it for later use. While testosterone is bound to SHBG, it is biologically inactive.
- Albumin-bound testosterone: The remainder of your testosterone is bound to a protein called albumin. It is bound to albumin for the same reasons: transport and storage. Like SHBG-bound testosterone, albumin-bound testosterone is biologically inactive. However, unlike SHBG-bound testosterone, the bond between albumin and testosterone is weak, and can therefore easily be broken in order to create free testosterone when needed.
Now that we understand that most of your testosterone is made in your testicles, and in which forms it is present in your body, let’s also understand how it’s made.
How Is Testosterone Produced?
The testosterone production process starts in your brain.
When the hypothalamus in your brain detects that your body needs more testosterone (to fulfill some task), it first produces a hormone called gonadotropin-releasing hormone.
This hormone then makes its way over to the pituitary gland in the back of your brain. When here, it instructs your pituitary gland to produce a hormone called luteinizing hormone.
This luteinizing hormone is then transported through the bloodstream to your testicles.
When the luteinizing hormone arrives, it stimulates cells called the leydig cells in your testicles to convert cholesterol to testosterone.
Now testosterone is being produced.
As it is produced, it’s released into your bloodstream. Here SHBG and albumin are waiting for it, and immediately start attaching themselves to the testosterone.
The small percentage of testosterone that remains free and unbound (about 1-3%), then circulates with the blood and starts to carry out tasks.
When your brain detects that you have enough testosterone in your blood, it asks the pituitary gland to stop secreting luteinizing hormone.
When this hormone stops arriving at your testicles, they slow down (or stop) producing testosterone.
By the way, this testosterone production takes place primarily at night when you sleep.
Therefore, your testosterone level is typically highest in the morning right after you wake up. And it’s also normally lowest in the evening before you go to bed.
As you probably realize, if you don’t sleep enough, you are also likely to be testosterone deficient.
To have an optimal level of testosterone, you need adequate sleep. Which for most men is 7 hours a night, or more.
The Link Between Testosterone, Libido And Erectile Dysfunction
Many people are probably aware that testosterone is somehow a key ingredient needed for a man to function sexually.
But how exactly does testosterone support erections, libido and what is the link to ED?
Let’s first explore the link between testosterone and libido.
Libido by the way, is what evolution endowed us with in order to motivate us to procreate.
At some point in evolution, our genes came up with an ingenious idea to increase the probability that we pass on our genes to the next generation.
They gave us libido. Libido made us want to have more sex. And as we had more sex, we had more offspring.
Dopamine is what motivates you to have sex.
Here is how it works:
When you feel some form of sexual stimulus (a kiss for instance), dopamine is produced in you brain.
As dopamine is created, it fires up the center in your brain that controls reward and desire. You now start desiring sex. And the more dopamine you produce, the stronger your desire.
Here is where testosterone enters the picture:
In order for dopamine to do its job properly, it needs testosterone. Testosterone regulates dopamine. In other words, without enough testosterone, your dopamine cannot do what it wants to do.
Hence little dopamine = little libido.
This is how testosterone and libido are linked.
Let’s also explore the links between testosterone and your ability to get erections.
Research studies also demonstrate that dopamine is critical in order for you to get erections.
As soon as dopamine has fired up craving for sex in your brain, it starts shooting signals down your spinal cord to your penis.
When these signals arrive, they instructs blood vessels in your penis to produce a gas called nitric oxide. This nitric oxide then opens up your blood vessels. Now blood rushes into your penis.
And an erection is being formed.
So in order to get an erection, not only do you need dopamine, but also nitric oxide.
And testosterone is also essential in order for nitric oxide to be produced.
Nitric oxide is produced by an enzyme called nitric oxide synthase. This enzyme is highly dependent on testosterone in order to function properly.
Therefore, you need a healthy level of testosterone in order to produce enough nitric oxide.
This is the key link between testosterone and your ability to get erections.
By the way, research studies on animals and humans have shown that castrated individuals (castration will normally lead to a significant reduction in testosterone production), tend to lose a significant amount of nitric oxide synthase activity compared to uncastrated individuals.
Additionally, research has shown that castrated subjects that have later undergone testosterone replacement therapy, have seen their nitric oxide synthase activity increase substantially.
Both these observations point to the importance of testosterone for your nitric oxide production.
But testosterone isn’t just important for dopamine and nitric oxide. No, testosterone is important for everything that happens in your body that is of a sexual nature.
Testosterone is essential for the upkeep of structural integrity of the corpus cavernosum, nerves and connective tissues in the penis.
In other words, if you lack testosterone over a period of time, integral features of your penis may decay.
This may in turn cause erectile dysfunction.
If you want to learn how to cure ED naturally and permanently, then you can read this guide.
Testosterone is also very important for the regulation of something called smooth muscle relaxation and contraction. This is what allows for appropriate bloodflow in and out of the penis.
Let’s have a look at what other roles testosterone plays in your body.
The Roles of Testosterone
Testosterone gets to work early. Before you were born actually.
Because during your prenatal development, testosterone played a key role in determining your gender.
After you were born, testosterone stimulated the development of your genitals and the prostate gland.
When you were a young boy, testosterone impacted your brain development forming characteristics such as high levels of activity, increased risk taking, exploration, need for dominance, etc.
In your late childhood, testosterone contributed to the growth of pubic hair, axillary hair, facial hair, increased oiliness of skin, and hair and acne formation.
If you saw a sudden growth and lengthening of your arms and legs just before reaching adolescence, you can attribute it in part to testosterone.
During adolescence, testosterone made you acquire a deeper voice, made your facial features take on a more defined contour, increased your muscle mass, made your shoulders broader, and made your Adam’s apple appear.
Also during adolescence, testosterone started to increase your sex drive.
And one of testosterone‘s key functions now, is to regulate your sperm production.
What else is testosterone doing in your body today?
Testosterone is a requirement for protein synthesis and production of growth hormone, both of which are needed for maintaining muscle mass, tissue growth, hair growth and bone formation.
Testosterone also assists with oxygen uptake throughout the body, helps control blood sugar, regulates cholesterol, and maintains the immune system.
In addition, your body requires testosterone in order to maintain efficient bloodflow from the heart (cardiac output), and for your bone marrow to manufacture red blood cells.
Testosterone also plays an important role in regulating glucose and fat metabolism.
Also, testosterone still plays a role in development of certain behaviors, including aggression, dominance, tolerance for risk-taking and the desire for power.
And it helps to spark competitiveness, increase self-esteem and higher levels of energy.
Let’s also understand how testosterone changes with age.
Testosterone And Aging
Testosterone levels peak in the late teens and then gradually decline over time, typically by about 1% a year after age 30.
As a result, many men will experience changes.
By age 50, most men notice that their sexual desires and sexual abilities have changed; it takes longer for the penis to become erect, and erections are often not as firm as before.
It may also take longer to achieve orgasm and to ejaculate.
Erectile dysfunction also becomes more common.
The decline in testosterone also plays an important role in a series of other changes that often accompany the ageing process. Such as a decline in muscle mass, strength and bone mass (osteoporosis), and an increase in abdominal fat.
However, getting older does not have to mean that your testosterone will be depressed.
Not at all.
Your body and mind can normally continue to function extremely well, well into old age. And you can keep a very high testosterone level.
All you need to do, is to live super healthy and maintain your body and mind in balance.
I plan on functioning super well sexually, even after turning 100 years old. Time will tell. 😉
Testosterone and Cholesterol
Before we finish, I wanted to add some words about the links between cholesterol and testosterone.
Testosterone and cholesterol are both steroids, and they share a similar chemical structure. Both are also important for many bodily functions.
Cholesterol is part of every cell‘s outer membrane, responsible for the fluid nature of the cells, and it also helps determine which molecules can enter the cells.
Cholesterol is made as needed by your body. You actually don’t need to consume cholesterol directly.
But if you eat animal-based products, you get additional cholesterol
When people speak of cholesterol, it is normally in a negative context. Cholesterol has a bad reputation.
This bad reputation comes primarily because cholesterol can cause plaque buildup inside your arteries (atherosclerosis), and as a result cardiovascular diseases.
These in turn, normally always stems from an unhealthy lifestyle.
Cholesterol however, does probably not deserve its bad reputation. Because it is absolutely essential for healthy bodily functions.
You need cholesterol.
And you need cholesterol in order to produce testosterone.
Because cholesterol is a precursor to testosterone, which means cholesterol is needed as a building block in order for testosterone to be produced.
Let’s look at how cholesterol and testosterone transported around the body.
Whereas testosterone is transported through the blood bound to SHGB and albumin, cholesterol gets attached to proteins called lipoproteins, which then transport cholesterol through the blood vessels.
Low-density lipoproteins and high-density lipoproteins both transport cholesterol in the blood, but they deliver cholesterol to different parts of the body.
Low-density lipoproteins bring cholesterol to the cells throughout the body as all cells need cholesterol to function optimally (also called ‘bad’ cholesterol).
It is called ‘bad’ because it may cause cholesterol to build up in the arteries. That happens if there is a larger supply of cholesterol than there is demand for it.
High-density lipoproteins carry cholesterol away from the cells and deliver it to the liver, where it is broken down and removed from the bloodstream (also called ‘good’ cholesterol).
The body needs a healthy balance of cholesterol and testosterone to function optimally, and too much of one normally means too little of the other.
For instance, an important role of testosterone is to enable and support high-density lipoproteins in the removal of excess cholesterol from the arteries, and transport it to the liver for destruction.
If you have inadequate testosterone, this may therefore cause a build-up of excess cholesterol.
In addition, obesity, which will normally be accompanied by excess cholesterol, will often lead to decreased testosterone levels.
Anderson RA, Bancroft J, Wu FC. The effects of exogenous testosterone on sexuality and mood of normal men. J Clin Endocrinol Metab. 1992;75:1503–1507.
Aversa A, Isidori AM, De Martino MU et al. Androgens and penile erection: evidence for a direct relationship between free testosterone and cavernous vasodilation in men with erectile dysfunction. Clin Endocrinol (Oxf) 2000; 53: 517-22.
Azadzoi KM, Kim N, Brown ML, Goldstein I, Cohen RA, Saenz de Tejada I. Endothelium-derived nitric oxide and cyclooxygenase products modulate corpus cavernosum smooth muscle tone. J Urol 1992; 147: 220-5.
Baba K, Yajima M, Carrier S, Morgan DM, Nunes L, Lue TF, Iwamoto T. Delayed testosterone replacement restores nitric oxide synthase-containing nerve fibres and the erectile response in rat penis. BJU Int. 2000 May; 85(7):953-8.
Bagatelle C, Heiman JR, Rivier RE, Bremmer WJ. Effects of endogenous testosterone and estradiol on sexual behavior in normal young men. J Clin Endocrinol Metab. 1994; 78:711–716.
Baskerville TA, Allard J, Wayman C, Douglas AJ. Dopamine-oxytocin Interactions in Penile Erection. Eur J Neurosci. 2009 Dec 3;30(11):2151-64. doi: 10.1111/j.1460-9568.2009.06999.x. Epub 2009 Nov 25.
Benkert O, Witt W, Adam W, Leitz A. Effects of testosterone undecanoate on sexual potency and the hypothalamic-pituitary-gonadal axis of impotent males. Arch Sex Behav. 1979; 8:471–480.
Blute M, Hakimian P, Kashanian J, Shteynshluyger A, Lee M, Shabsigh R. Erectile dysfunction and testosterone deficiency. Front Horm Res. 2009; 37:108-22. DOI: 10.1159/000176048.
Boloña ER, Uraga MV, Haddad RM, Tracz MJ, Sideras K, Kennedy CC, Caples SM, Erwin PJ, Montori VM. Testosterone Use in Men With Sexual Dysfunction: A Systematic Review and Meta-analysis of Randomized Placebo-Controlled Trials. Mayo Clinic Proceedings, Jan 2007,82(1):20-28.
Buena F, Swerdloff R, Steiner BS, et al. Sexual function does not change when serum testosterone levels are pharmacologically varied within the normal male range. Fertil Steril. 1993; 59:1118–1123.
Burnett AL. Novel nitric oxide signaling mechanisms regulate the erectile response. Int J Impot Res 2004; 16 (Suppl. 1): S15-9.
Buvat J, Lemaire A, Buvat-Herbaut M. Human chorionic gonadotropin treatment of nonorganic erectile failure and lack of sexual desire: a double-blind study. Urology. 1987; 30:216–219.
Chamness SL, Ricker DD, Crone JK, Dembeck CL, Maguire MP, Burnett AL, Chang TS. The effect of androgen on nitric oxide synthase in the male reproductive tract of the rat. Fertil Steril, 1995 May, 63(5):1101-7.
Davidson JM, Camargo CA, Smith ER. Effects of androgen on sexual behavior in hypogonadal men. J Clin Endocrinol Metab. 1979; 48:935–941.
Du J, Hull EM. Effects of testosterone on neuronal nitric oxide synthase and tyrosine hydroxylase. Brain Res. 1999 Jul 31; 836(1-2):90-8.
Foresta C, Caretta N, Rossato M, Garolla A, Ferlin A. Role of androgens in erectile function. J Urol 2004; 171: 2358-62.
Goh VH, Tong TY. Sleep, sex steroid hormones, sexual activities, and aging in Asian men. J Androl. 2010 Mar-Apr; 31(2):131-7. DOI: 10.2164/jandrol.109.007856.
Granata AR, Rochira V, Lerchl A, Marrama P, Carani C. Relationship between sleep-related erections and testosterone levels in men. Journal of Andrology, 18(5):522-527.
Gray PB, Singh AB, Woodhouse LJ, Storer TW, Casaburi R, Dzekov J, Dzekov C, Sinha-Hikim I, Bhasin S. Dose-Dependent Effects of Testosterone on Sexual Function, Mood, and Visuospatial Cognition in Older Men. J Clin Endocrinol Metab. 2005 Jul; 90(7):3838-46.
Giuliano F, Allard J. Dopamine and Sexual Function. Int J Impot Res. 2001 Aug;13 Suppl 3:S18-28. doi: 10.1038/sj.ijir.3900719.
Handelsman DJ, Zajac JD. Androgen deficiency and replacement therapy in men. Med J Aust 2004; 180: 529-35.
Huo S, Scialli AR, McGarvey S, Hill E, Tügertimur B, Hogenmiller A, Hirsch AI, Fugh-Berman A. Treatment of Men for “Low Testosterone”: A Systematic Review. PLoS One. 2016 Sep 21;11(9):e0162480. DOI: 10.1371/journal.pone.0162480. eCollection 2016.
Isidori AM, Giannetta E, Gianfrilli D et al. Effects of testosterone on sexual function in men: results of a meta-analysis. Clin Endocrinol (Oxf) 2005; 63: 381-94.
Jannini EA, Screponi E, Carosa E et al. Lack of sexual activity from erectile dysfunction is associated with a reversible reduction in serum testosterone. Int J Androl 1999; 22: 385-92.
Morales A, Johnston B, Heaton JP, Lundie M. Testosterone supplementation for hypogonadal impotence: assessment of biochemical measures and therapeutic outcomes. J Urol. 1997; 157:849–854.
Morelli A, Filippi S, Mancina R et al. Androgens regulate phosphodiesterase type 5 expression and functional activity in corpora cavernosa. Endocrinology 2004; 145: 2253-63.
Morley JE, Kaiser FE, Perry HM, et al. Longitudinal changes in testosterone, luteinizing hormone and follicle stimulating hormone in healthy old men. Metabolism. 1997; 46:410–413.
McBride JA, Carson CC III, Coward RM. Testosterone deficiency in the aging male. Ther Adv Urol. 2016 Feb; 8(1): 47–60. DOI: [10.1177/1756287215612961].
Mulhall JP, Valenzuela R, Aviv N, Parker M. Effect of testosterone supplementation on sexual function in hypogonadal men with erectile dysfunction. Urology 2004; 63: 348-52.
O’Carroll R, Bancroft J. Testosterone therapy for low sexual interest and erectile dysfunction in men: a controlled study. Br J Psychiatry. 1984; 145:146–151.
Park KH, Kim SW, Kim KD, Paick JS. Effects of androgens on the expression of nitric oxide synthase mRNAs in rat corpus cavernosum. BJU Int 1999; 83: 327-33.
Penev PD. Association between sleep and morning testosterone levels in older men. Sleep. 2007 Apr; 30(4):427-32.
Pirke KM, Kockott G, Aldenhoff J, et al. Pituitary gonadal system function in patients with erectile impotence and premature ejaculation. Arch Sex Behav. 1979; 8:41–48.
Rastrelli G, Corona G, Maggi M. Testosterone and sexual function in men. Maturitas. 2018 Jun;112:46-52. DOI: 10.1016/j.maturitas.2018.04.004. Epub 2018 Apr 6.
Rajfer J. Relationship Between Testosterone and Erectile Dysfunction. Rev Urol. 2000 Spring; 2(2): 122–128.
Salminies S, Kockott G, Pirke KM, et al. Effects of testosterone replacement on sexual behavior in hypogonadal men. Arch Sex Behav. 1982; 11:345–353.
Schiavi RC, White D, Mandeli J, Levine AC. Effect of testosterone administration on sexual behavior and mood in men with erectile dysfunction. Arch Sex Behav 1997; 26: 231-41.
Shabsigh R. The effects of testosterone on the cavernous tissue and erectile function. World Journal of Urology, 15(1):21-26.
Shabsigh R. The role of testosterone in the cavernous tissue and its neural supply. World J Urol 1997; 15: 21-6.
Sternbach H. Age-Associated Testosterone Decline in Men: Clinical Issues for Psychiatry. Am J Psychiatry. 1998 Oct; 155(10):1310-8.
Szczypka MS, Zhou QY, Palmiter RD. Dopamine-stimulated Sexual Behavior Is Testosterone Dependent in Mice. Behav Neurosci. 1998 Oct;112(5):1229-35. doi: 10.1037//0735-7044.112.5.1229.
Tenover JL. Testosterone and the aging male. J Androl. 1997; 18:103–106.
Travison TG, Morley JE, Araujo AB, O’Donnell AB, McKinlay JB. The Relationship between Libido and Testosterone Levels in Aging Men. J Clin Endocrinol Metab. 2006 Jul; 91(7):2509-13.
Tyagi V, Scordo M, Yoon RS, Liporace FA, Greene LW. Revisiting the role of testosterone: Are we missing something? Rev Urol. 2017;19(1):16-24.
Wheeler MJ. The determination of bio-available testosterone. Ann Clin Biochem. 1995; 32:345–357.
Yassin AA, Saad F. Improvement of Sexual Function in Men with Late-Onset Hypogonadism Treated with Testosterone Only. The Journal of Sexual Medicine, Mar 2007, 4(2):497-501.
Zhang XH, Morelli A, Luconi M, Vignozzi L, Filippi S, Marini M, Vannelli GB, Mancina R, Forti G, Maggi M. Testosterone regulates PDE5 expression and in vivo responsiveness to tadalafil in rat corpus cavernosum. Eur Urol 2005; 47: 409-16.
Zvara P, Sioufi R, Schipper HM, Begin LR, Brock GB. Nitric oxide mediated erectile activity is a testosterone dependent event: a rat erection model. Int J Impot Res. 1995 Dec; 7(4):209-19.