Introduction

This section explains what testosterone is, in which forms it is present in the human body, the roles of testosterone throughout our life-stages, how testosterone affects erectile functioning as well as how a lack of it can lead to erectile dysfunction and a reduced libido.

 

Testosterone

Testosterone is what is called a steroid hormone and which belongs to the androgen group. Androgens stimulate and control the development and maintenance of male characteristics and sexual development. A small percentage of testosterone is made in the adrenal glands on top of our kidneys, however about 95% of it is made in the testicles. Levels of testosterone are about 7–8 times greater in adult males than in adult females, but, as the consumption of testosterone in males is greater, the daily production is about 20 times greater in men. On average, a man’s body produces about 7 mg of testosterone a day, but not all of that testosterone can be immediately used by the body because it is bound to proteins and therefore made inactive. Testosterone is present in the body in the following three forms:

  • Free Testosterone: This is testosterone in its optimal and purest form. The reason it’s called ‘free’ is because there aren’t any proteins attached to it. Unbound to other molecules, free testosterone can go about carrying out its functions freely by entering cells and activating receptors. Free testosterone normally makes up only 1-3% of a man’s total testosterone levels.
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The testosterone production process starts in the brain. When our hypothalamus detects that our body needs more testosterone to fulfill some task, it secretes a hormone called gonadotropin-releasing hormone. This hormone makes its way over to the pituitary gland in the back of the brain. When the pituitary gland detects the gonadotropin-releasing hormone, it starts producing a hormone called luteinizing hormone. This hormone is then transported through the bloodstream to the testicles. In the testicles, it stimulates the leydig cells to convert cholesterol to testosterone. Once testosterone is produced, it is released into our bloodstream. Most of it immediately gets bound to SHBG and albumin and become biologically inert.

The small percentage of testosterone that remains free and unbound (1-3%) circulates around the blood vessels and carries out the normal functions of testosterone. When the brain detects that there is enough testosterone in the blood, it signals the pituitary gland to stop secreting luteinizing hormone so that the testicles can slow down or stop testosterone production.

Testosterone production takes place primarily at night when the body is sleeping. This manufacturing of testosterone normally peaks about three hours into the sleep, and also normally continues for as long as a person is sleeping. Therefore, testosterone levels are typically highest in the morning right after a person wakes up, and are also normally lowest in the evening before bedtime.

 

Testosterone and Cholesterol

Testosterone and cholesterol are both called steroids because they share a similar chemical structure, and both are also important for many bodily functions. Cholesterol is part of every cell‘s outer membrane, responsible for its fluid nature and helping determine which molecules can enter the cells. The body can obtain cholesterol from animal-based foods, but it’s also made as needed by the liver and other organs. Cholesterol has a bad reputation primarily for causing cardiovascular disease, however it is an absolutely essential molecule for healthy bodily functions.  

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Cholesterol is a also a precursor of testosterone, which means cholesterol is needed as a building block in order for testosterone to be produced. 

Whereas testosterone is transported through the blood bound to SHGB and albumin, cholesterol is combined with proteins called lipoproteins, which transport cholesterol through the blood vessels to reach cells and tissues. 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, the primary carriers of cholesterol and also called ‘bad’ cholesterol, bring cholesterol to cells throughout the body as all cells need cholesterol to function optimally. It is called ‘bad’ because it may cause cholesterol to build up in the arteries if there is more supply of cholesterol than there is demand for it from the body. High-density lipoproteins, called ‘good’ cholesterol, carry cholesterol away from the heart and other organs and deliver it back to the liver, where it is broken down and removed from the bloodstream. 

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. Inadequate testosterone 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.

 

The Roles of Testosterone

As early as during prenatal developmenttestosterone takes part in human formation by playing a key role in determining the gender of the embryo. After birth, the presence of testosterone stimulates the development of the male sex organs and the prostate gland.

In very young boys, testosterone impacts brain development leading to development of characteristics such as high levels of activity, increased risk taking, exploration, need for dominance, etc.

In late childhood, testosterone contributes to the growth of pubic hair, axillary hair, facial hair, increased oiliness of skin and hair and acne formation. Boys will often also witness a sudden growth and lengthening of arms and legs due to bone maturation just before reaching adolescence.

During adolescence, testosterone makes boys acquire a deeper voice, makes facial features take on a more defined contour, increases muscle mass, makes shoulders broader, makes hair growth increase overall, and makes the Adam’s apple appear. During adolescence, testosterone will also cause young men to experience an increase in sexual desire.

During adulthood, one of testosterone‘s key functions is to regulate sperm productionTestosterone is also 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. 

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Testosterone also assists with oxygen uptake throughout the body, helps control blood sugar, regulates cholesterol, and maintains the immune system. In addition, the body requires testosterone to maintain efficient bloodflow from the heart (cardiac output) and for the bone marrow to manufacture red blood cellsTestosterone also plays an important role in regulating glucose and fat metabolism.

Testosterone also plays a role in development of certain behaviors, including aggression, dominance, tolerance for risk-taking and the desire for power. It also helps to spark competitiveness, increase self-esteem and contribute to higher levels of energy.

Testosterone levels peak in the late teens and then gradually decline over time, typically by about 1% a year after age 30. By age 60 to 65, though usually earlier, most men notice that their sexual inclinations and sexual abilities have changed; it takes longer for the penis to become erect and erections may not be as firm as before. It may also take longer to achieve orgasm and to ejaculate. Erectile dysfunction also becomes more common. This decline in testosterone plays an important role in a series of signs and symptoms that accompany the ageing process, such as a decline in virility, libido, sexual activity, muscle mass, strength and bone mass (osteoporosis) as well as an increase in abdominal fat.

 

Testosterone, ErectionsLibido 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 how does it impact erectile dysfunction?

When the penis is in a flaccid state, the smooth muscles in the penis are in a state of contraction and therefore clench around the blood vessels. When this happens, blood is squeezed out of the penis and the only blood that is allowed to enter is for maintenance purposes. In order for a penis to become erect, blood needs to flow into the penis to fill it to its capacity. For this to happen, help is needed from a molecule called nitric oxide. Nitric oxide, when diffused into the smooth muscles of the penis, makes these smooth muscles start to relax and therefore give up the tight grip around the blood vessels. When this happens, blood is allowed to flow into the penis and an erection can be built. This nitric oxide is created by an enzyme called nitric oxide synthase. To learn more about nitric oxide on Truelibido, please go here.

Nitric oxide synthase is highly dependent on testosterone to function properly, and low levels of testosterone will normally cause these enzymes to produce low levels of nitric oxide. The reason is that low levels of testosterone will normally lead to a decrease in the number of active nitric oxide synthase neurons in the brain. In other words, these neurons that communicate with nitric oxide need testosterone to operate. 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, castrated subjects that have later undergone testosterone replacement therapy, have seen their nitric oxide synthase activity increase substantially.

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Not only is nitric oxide synthase dependent on testosterone to carry out its tasks and function properly, but so is the messenger molecule dopamine. In order for adequate levels of dopamine to be produced, testosterone is needed. An environment with adequate levels of testosterone provides the basis for dopamine synthesis. Dopamine is a key element in libido and is also paramount for a penile erection to take place. It provides the basis for libido and is one of the first chemicals to act in the erection process by setting off a cascade of events among chemicals such as nitric oxide, serotonin, testosterone and others. In addition, these three moleculestestosterone, dopamine and nitric oxide – are interconnected and impact each other further as increased nitric oxide production in turn causes further dopamine release, which again further support both libido and erectile functioning. To learn more about dopamine on Truelibido, please go here.

Research has also found that testosterone has a profound effect on the functional and structural integrity of the corpus cavernosum, nerves and connective tissues in the penis, and particularly on the regulation of smooth muscle relaxation and contraction that allows for appropriate bloodflow in and out of the penis. In other words, if there is a lack of testosterone over a significant period of time, a person may experience a decay of integral features of the penis – the penis may stop working properly – and erectile dysfunction may kick in as a result. To learn more about erectile dysfunction on Truelibido, please go here.

 

Research Studies

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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.

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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.

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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.

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