The functions of testosterone

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The functions of testosterone

The testosterone is a steroid hormone that belongs to the category of androgen hormones; it is produced by the interstitial cells of the testicle (Leydig cells) by the action of the luteinizing hormone (LH) which is secreted by the lower pituitary.

Testosterone is formed from cholesterol through two processes, the first of which is the most used in the testicles. The production, albeit in more limited quantities, also takes place at the adrenal level (by conversion of androstenediol) and in the ovary.

In the human body, it is produced from cholesterol (for further information on this point it is advisable to consult the article Metabolism of androgens).

Testosterone secretion follows a circadian rhythm; the blood peak is reached in the very first morning hours, after which there is a progressive drop; the minimum peak is around 18.00. Low levels of the hormone are found in the case of cirrhosis of the liver, renal insufficiency, estrogen therapy and food imbalances (malnutrition and obesity).

There are numerous functions that testosterone performs in our body; these functions are different in relation to the different stages of life; let's see the main ones.

During the prenatal period (roughly between the seventh and twelfth week of gestation) it regulates the development of the prostate and seminal vesicles; it also takes part in the development of the external genital organs, although the main role, in this case, is played by dihydrotestosterone (DHT).

Its role in early childhood has not been defined with certainty; testosterone levels during this period of life, in fact, are quite low and it is not entirely certain that they can cause changes of a certain importance. Years ago, it was thought that, although low, these hormone levels could still have some influence on the child's behavior, but this role is delegated to estrogen.

During the pre-pubertal period, the distinctive characteristics of the male and female sex are determined. During these years we have witnessed the growth of hair, especially of the pubic and axillary hair. Testosterone is converted into dihydrotestosterone due to an increased expression of the enzyme 5-alpha-reductase type 2; the increased levels of DHT increase the expression of male characteristics.

During puberty, free testosterone levels peak. In this period of life, there is a significant growth of the sebaceous glands, penis, and clitoris; the levels of hypodermic fat are reduced, the vocal timbre is lowered, an important muscle growth and also a notable bone growth are registered; the skeletal system is strengthened. On the skeletal system, testosterone also acts by limiting the lengthening of long bones; this means that there is no disproportionate growth of the limbs.

Once we reach adulthood, starting from the age of about 40, hormone levels gradually begin to decrease by about 1% per year). During adulthood, testosterone is involved not only in behavior cypionate 250 en venta en espana and in maintaining muscle tone, but also in sexual desire and in maintaining an erection.

Converted in part into estrogen, it protects the male from the risk of osteoporosis, promoting the deposition of calcium in the bones.

Some authors also speak of increased insulin sensitivity and a decrease in cardiovascular risk (which contrasts with the fact that high cholesterol, necessary for good testosterone production, should increase this risk).

If an excessive amount of testosterone turns into DHT (dihydrotestosterone), baldness originates, as DHT binds to the hair bulb of the hair, atrophying it. The drugs used to block this conversion often lead to excessive amounts of free testosterone in the blood, resulting in conversion to estrogen (due to the action of the aromatase enzyme) with a decrease in libido and an increase in body fat.

Free and total testosterone

Only a small part of testosterone in the blood circulates freely and is able to penetrate the cells (in this case we speak of free testosterone); the majority (around 98% in men and around 99% in women), on the other hand, are linked to proteins (according to the known mechanism for transporting a hormone, or protein + hormone); in fact, about 44% is linked to sex hormone-binding globulin (Sex Hormone Binding Globulin, SHBG), about 4% is linked to cortisol binding globulin (Cortisol Binding Protein, CBG) and about 50% is bound to albumin with a weaker link.

Basically, only about 2% of testosterone is free. Since the quantity bound to the protein is inactive (to activate it must break the bond with the protein), it does not make sense to measure the total testosterone, it would be necessary to measure the free one. In fact, in old age (or in alcoholics and in subjects suffering from hypothyroidism ) the production of SHBG has increased and the free fraction is further reduced.

Depending on metabolic demands, a small portion of the hormone-protein bond can break down and testosterone is free to penetrate cells by regulating gene transcription.

If there is an excess of free circulating testosterone, the body is able to neutralize it through a transformation into estradiol (a female hormone) which occurs mainly at the level of the central nervous system and adipose tissue.

Understanding test - From the above, it should be clear that, since the free fraction is only a small percentage, it is better to have 4 ng / ml of total testosterone and 2% free than 7 ng/ml of total and 1 % free.

Therefore, when you hear someone attributing any effect on an organism to too low a testosterone value, ask them if they are talking about the free one or if they are discussing the total one. If it falls from the clouds, forget all his advice.

Unfortunately, if the determination of the total fraction is not very significant, the free testosterone dosages that are carried out by the common analysis laboratories, besides being quite expensive, are not particularly reliable. At present, the method that shows the best reliability for the dosage of the free quota is the one that uses equilibrium dialysis (a particularly expensive method and therefore used very rarely).

The value of the free testosterone can be obtained, with a sufficient approximation, through the so-called Vermeulen formula; knowing the values of albumin, SHBG and total testosterone and using an online calculator, it will be possible to obtain, as has been confirmed by some studies, reliable values of free testosterone.

Below are the blood reference values of total testosterone:


  • 7-9 years - <9 ng / dL
  • 10-11 years - 2-57 ng / dL
  • 12-13 years - 7-747 ng / dL
  • 14-15 years - 33-585 ng / dL
  • 16-17 years - 185-886 ng / dL
  • 18-39 years - 300-1.080 ng / dL
  • 40-59 years - 350-890 ng / dL
  • > 60 years - 300-720 ng / dL.


  • 7-9 years - <15 ng / dL
  • 10-11 years - 2-42 ng / dL
  • 12-13 years - 6-64 ng / dL
  • 14-15 years - 9-49 ng / dL
  • 6-17 years - 8-63 ng / dL
  • 8-30 years - 11-59 ng / dL
  • 1-40 years - 11-56 ng / dL
  • 41-51 years old - 9-55 ng / dL
  • Postmenopause - 6-25 ng / dL.

Testosterone and sport

The testosterone level increases significantly during exercise and often remains high again an hour after the end. It is verified that in concomitance with the maximum peak of the athlete's form the levels are generally lower, (i.e. the increase is less), a sign of an adaptation to the stress induced by the training. This figure is very important because it indicates that testosterone is not an absolute bottleneck: if it is important to have minimum levels to obtain the best performance, having very high levels is not a guarantee of improved performance. In particular, the data on the levels of this hormone in cross-country races such as the marathon is not consistent (Kuoppasalmi, 1980, Ponjee, 1994 and Vogel, 1985).

Testosterone control is not a routine check, except for those subjects who have very low total cholesterol values (less than 160 mgmg mgl for the sportsman it is sufficient to check it every 3-5 years to track its evolution over time. As with all hormones, the test for the detection of testosterone levels must be conducted in sport and non-sports conditions of rest and non-administration of drugs (estrogen, barbiturates, thyroid drugs, etc.) for at least 48 hours.

Is it possible to increase testosterone levels with supplementation?

Currently, there is no supplement capable of significantly increasing free testosterone levels for a sufficient time, without important side effects and capable of generating an increase in muscle mass.

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