Testosterone 101: The Science

Drew "Vanilla Gorilla" Peters Supplement Knowledge Leave a Comment

One of the most crucial hormones in the human body is also consequently one of the biggest lightning rods of controversy in the health community. Misunderstood for many reasons in regards to what it is, what it does and the applications it is used for, testosterone is a hot topic that isn’t going away anytime soon, and rightfully so. If you were to conduct a survey, most if not all of the participants would have at least heard of this hormone, as few other hormones can rival the common awareness of it. Unfortunately, however, many aren’t familiar with exactly what this hormone does, how it works or where it comes from. The purpose of this article is to cover just what testosterone is, what it does, where it comes from (natural & synthetic) and give a brief overview of a few other related matters.

Testosterone – What is it?

Technically speaking on the physiological level, testosterone is a 19-carbon steroid hormone produced in the Leydig cells (in men) and the ovaries (in women) (1). It belongs to the androgen class of hormones, which also include the hormones androstendione, dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT), and androstendiol (2). These are not to be confused with the other six classes of steroid hormones which include progestins, estrogens, mineralcorticoids, glucocorticoids, Vitamin D and bile acids (3).

Testosterone is the dominant sex hormone in men, and for average males, the average production is about seven mg of testosterone per day, putting normal blood values between 300 and 1000 ng/dL (10-28 nmol/L). Females on the other hand, while it isn’t their dominant sex hormone still produce testosterone at about 1/15th this amount with normal blood levels of 25 to 90 ng/dL (1-2.5 nmol/L) (4).

To get a little further into detail, it is important to note that within the bloodstream, when testosterone enters the bloodstream; roughly 96% of it is bound to a albumin and globulin, proteins that assist in keeping blood from leaking out of blood vessels (5). This binding may sound like a fairly high amount, but it serves 3 purposes. The first is that it makes testosterone soluble for blood transport, secondly it protects the hormone from degradation in the kidneys and liver and lastly it serves as a built-in reservoir that helps prevent possible fluctuations in plasma testosterone levels (6). The remaining portion of testosterone that isn’t bound to albumin or globulin, is appropriately named “free testosterone” and is the biologically active fraction of the hormone, meaning it is free to interact with the various tissues of the body such as skeletal muscle and cause physiological changes (7).

The testosterone levels are regulated by two key factors in the body. The first is the total amount of testosterone in the blood and the second is the binding capacity of the plasma proteins. There is an inverse relationship between the two as when binding capacity rises, the levels of free testosterone are lowered. The binding ability in the bloodstream and resulting higher level of free testosterone can be altered by way of drugs such as anabolic steroids, insulin or other synthetic hormones but have also shown alterations with natural ergogenic aids such as Tribulus, d-aspartic acid, etc (8). On the other side of the coin, there is mounting evidence that environmental pollution and contaminants can actually have the opposite effect, and make for less free testosterone (9).

It is also important to make note that of the free testosterone in the body, much of it is converted by the 5-alpha reductase enzyme to a more potent androgen, dihydrotestosterone (DHT) (10). The other thing that testosterone can convert to is estrogens such as estradiol, estriol and estrone and this is regulated by the aromatase enzyme complex and occurs mainly in the liver, brain and fat tissue (11).

Testosterone – What Does It Do?

Testosterone plays many roles in the human body for both sexes, but this is especially prevalent in men. An illustrative but not exhaustive list includes the following effects that testosterone plays in the male body:

  • Deepening of the voice (enlargement of the larynx during puberty)
  • Sperm production and formation
  • Increase in sex drive (libido)
  • Increase in muscle protein synthesis; Results in increased muscle mass
  • Magnified calcium retention in bones
  • Red blood cell number and total blood volume increases
  • Raise in basal metabolic rate
  • Glycogen breakdown in skeletal muscle is reduced during training
  • Growth of male sex organs during puberty
  • Hair growth stimulation in male characteristic areas such as chest, face, etc.

For females, testosterone plays a part as well in the body, predominantly influencing the growth, maintenance, and repair of reproductive tissues and secondarily skeletal muscle and metabolism.

From The Lows to the Highs – Varying Testosterone Levels

For men, one of the negatives of aging is decreased levels of testosterone in the body; however, this can also be a problem for younger individuals if there is an endocrine disorder. Since testosterone is the hormone most responsible for male sex drive, one of the negatives of low testosterone can include things such as issues with sexual function meaning a reduced sex drive, fewer erections and even a higher chance of infertility (12).

Another primary issue with decreased testosterone in men is physical changes such as an increase in body fat, decreased muscle mass, increased fatigue, negative cholesterol metabolism effects, increased fragility in bones and swelling/tenderness of the breast tissue. Additionally, low testosterone can cause issues with emotional state such as sadness or depression for some individuals. Lastly, it can even affect your sleep if testosterone levels are low causing insomnia, but interestingly testosterone replacement therapy has been researched to investigate its role in increasing the occurrence of sleep apnea (13).

There are many things that can cause low testosterone. Aside from the natural decline of testosterone production that comes from aging, things like an injury to the testicles, medication side effects, alcohol use, genetic abnormalities, nutrition disorders, pituitary gland problems, thyroid conditions, testicular cancer and other environmental factors can all negatively affect testosterone levels (14).

On The Rise – How to Increase Testosterone Naturally

On the flip side, there are things that have been shown to elevate natural testosterone levels including high intensity interval training, resistance training, optimized vitamin D levels, stress reduction, increased fat consumption as well as certain supplements such as d-aspartic acid, ashwagandha, and fenugreek (15).

Diet & Supplementation

One of the most crucial areas you can address in increasing natural testosterone levels is that of your nutrition, specifically the aforementioned fat and cholesterol intake. Dietary fat is actually one of the most critical players when it comes to optimizing natural testosterone production in regards to diet. One study that examined men who switched from a high-fat diet, consisting of 13% saturated fat to one that was low-fat consisting of 5% saturated fat had a significant reduction in testosterone production (16). Additionally, there has been demonstrated that overall higher amounts of both monosaturated and saturated fats can increase testosterone levels naturally (17).

Another dietary measure that has been demonized for years, much like dietary fat is that of dietary cholesterol. On a chemistry level, testosterone is derived from cholesterol, so if there is a lack of dietary cholesterol, then there will also be a deficiency in available material for testosterone production. There has been a strong correlation between free testosterone levels and HDL shown in research, so making sure your “good” cholesterol, HDL is sufficient (18). Interestingly, in regards to a food that has been demonized time and again, the whole egg has also been shown to have positive effects. In one study, it was shown that adding whole eggs into a moderate carbohydrate diet helped improve the HDL cholesterol levels and reduce insulin resistance in individuals experiencing metabolic syndrome (19).

In regards to supplements, fenugreek, zinc and d-aspartic acid have shown positive effects in increasing natural testosterone levels. For fenugreek, it was found that six weeks of supplementing with a formula containing fenugreek as a major ingredient showed significant increases in performance, sexual function, and satisfaction in healthy adult males (20).

An essential mineral, Zinc plays a critical role in testosterone production. Common among men and women in the United States, mild zinc deficiency has been associated with suppressed testosterone concentrations. One study, for example, has found that older men who had a mild zinc deficiency significantly increased their testosterone from 8.3 to 16.0 nmol/L (93% percent increase) following six months of zinc supplementation (21). Another essential diet based vitamin that can be supplemented is Vitamin D. The relationship between vitamin D supplementation and testosterone levels in men has shown a strong correlation with those ingesting adequate Vitamin D showing significantly higher levels of free testosterone compared to those with insufficient levels of vitamin D (22).

One of the most popular ingredients in testosterone boosting supplements these days for increasing testosterone naturally is d-aspartic acid (DAA) which is an amino acid present in neuroendocrine tissues. It has been shown to increase the activity of testosterone production in numerous instances. In one such study, researchers had 23 men take a daily dose of 3,120 mg of DAA for 12 days and another group receive a placebo. It was found that just after just 12 days, the subjects supplementing with DAA exhibited an average of 42 percent increase in testosterone and a 33% increase in luteinizing hormone (LH) (23).

Training & Recovery

The other crucial aspect for raising testosterone levels naturally lie in your training and rest. Specifically for training, resistance training has a large effect on natural testosterone levels. It has been demonstrated in numerous studies that high-intensity weight training (defined by weight in which failure is reached by 10 reps) can profoundly stimulate an increase in testosterone secretion. Specifically, it is supported that the more muscle mass that is stimulated, the greater testosterone elevation. Supporting such for example is a study that was conducted on trained subjects that resulted in squats stimulating a greater testosterone response when compared to leg press. To capitalize on this in your training, make sure to use multi-joint exercises like squat, deadlift, bench press in priority over machines or less intense exercises when possible (24).

As equally important is the time spent NOT in the gym. What we mean by this is that the duration of workouts can end up being counterproductive. It has been shown that regular practice of lengthy, drawn-out workouts with long rest periods or excessive endurance exercise can negatively impact testosterone levels. This is in part because workouts that last longer than an hour can start to negatively impact hormones not only reducing testosterone production but also increasing cortisol. To counteract this it has been suggested in research that a shorter rest period between sets (1 minute vs. 3 minutes) resulted in higher acute hormonal responses following resistance training, so keep rest periods short and workouts no longer than 60 minutes for most individuals (25).

Lastly, make sure that adequate sleep is attained as a crucial part of optimizing testosterone levels. It has been shown that a lack of quality sleep can have a drastic negative effect on the amount of testosterone your body produces. It has been demonstrated that the amount of sleep an individual gets is associated with testosterone levels after rising in the morning. One study showed that after recording the sleeping patterns of healthy men, it was found that participants’ testosterone levels increased the longer they slept and that 7-9 hours of sleep is optimal (26).

Natural Testosterone vs. Synthetic

One last area that has a lot of confusion that we will address is the difference between natural vs. synthetic testosterone. Simply put, endogenous (natural) testosterone is what the body produces naturally from within while exogenous (synthetic) testosterone is a chemically engineered version.

A further differentiating factor is that while synthetic testosterone of all forms are considered anabolic-androgenic steroids (AAS), there is a difference between medically prescribed purpose and recreational. For the testosterone deficient individual that goes to the doctor, they can be prescribed testosterone replacement therapy, which means they are given synthetic testosterone at a dosage that mimics the naturally occurring levels that the human body would produce. Recreational use such as in the case of bodybuilding or other physique enhancement purposes are typically taken at much higher doses than medical necessity and can combine one or more versions of the synthetic version to have various effects.


As you can see, testosterone has a wide array of effects in the human body, especially for males. It is one of the most misunderstood, yet popular hormones in modern society, and we hope that with this article you have more insight of what testosterone is, what it does, why low testosterone can be negative and the difference between natural and synthetic testosterone.


  1. Sargis, R.An Overview of the Testes. Endocrine Web. [Online] [Cited: January 10, 2017.] https://www.endocrineweb.com/endocrinology/overview-testes.
  2. Tulane University.The Hormones: Androgens. E.Hormone.tulane.edu. [Online] [Cited: January 10, 2017.] http://e.hormone.tulane.edu/learning/androgens.html.
  3. Introduction to Steroid Hormones. The Medical Biochemistry Page. [Online] [Cited: January 10, 2017.] http://themedicalbiochemistrypage.org/steroid-hormones.php.
  4. Severson, Alexia.Testosterone Levels by Age. HealthLine. [Online] [Cited: January 12, 2017.] http://www.healthline.com/health/low-testosterone/testosterone-levels-by-age#Overview1.
  5. Mayo Clinic.Testosterone, Total, Bioavailable, and Free, Serum. The Mayo Clinic. [Online] [Cited: January 12, 2017.] http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/83686.
  6. Nguyen, R.The Science Behind Testosterone Biomarkers. InsideTracker. [Online] February 26, 2014. [Cited: January 12, 2017.] https://www.insidetracker.com/blog/post/77907963875/the-science-behind-testosterone-biomarkers#.
  7. University of Rochester.Free Testosterone. Health Encyclopedia. [Online] University of Rochester. [Cited: January 12, 2017.] https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=testosterone_free.
  8. Sinja, S.Total T or Free T: Which is the Better Test for Androgen Deficiency? Hypogonadism Research Center. [Online] Medpage Today. [Cited: January 12, 2017.] http://www.medpagetoday.com/resource-center/hypogonadism/androgen-deficiency-testing/a/34999.
  9. Exposure to urban stressors and free testosterone plasma values. Sanici, A.6, August 2011, International Ach Occ Environ Health, Vol. 84, pp. 609-616.
  10. Belgravia Centre.What is DHT? Belgravia Centre Blog. [Online] [Cited: January 12, 2017.] http://www.belgraviacentre.com/blog/what-is-dht/.
  11. Estrogen Actions in the Brain and the Basis for Differential Action in Men and Women: A Case for Sex-Specific Medicines. Gillies, G.2, JUne 2010, Vol. 62, pp. 155-198.
  12. Effects of Testosterone Treatment in Older Men. Snyder, P.February 18, 2016, The New England Journal of Medicine, Vol. 374, pp. 611-624.
  13. Testosterone therapy and obstructive sleep apnea: is there a real connection? Hanafy, H.5, September 2007, Journal of Sex Medicine, Vol. 4, pp. 1241-1246.
  14. Gotter, A.Low Testosterone In Men. HealthLine. [Online] July 18, 2016. [Cited: January 13, 2017.] http://www.healthline.com/health/side-effects-of-low-testosterone#Overview1.
  15. An update on testosterone, HDL and cardiovascular risk in men. Thirumalai, A.3, 2015, Journal of Clinical Lipidology, Vol. 10, pp. 251-258.
  16. Effects of dietary fat and fiber on plasma and urine androgens and estrogens in men: a controlled feeding study. Dorgan, J.6, December 1996, American Journal of Clinical Nutrition, Vol. 64, pp. 850-855.
  17. Testosterone and cortisol in relationship to dietary nutrients and resistance exercise. Volek, J.1, January 1997, Vol. 82, pp. 49-54.
  18. Relationship of high density lipoprotein cholesterol with total and free testosterone and sex hormone binding globulin. Heller, R.2, October 1983, Acta Endocrinology (Copenh), Vol. 104, pp. 253-256.
  19. Whole egg consumption improves lipoprotein profiles and insulin sensitivity to a greater extent than yolk-free egg substitute in individuals with metabolic syndrome. Blesso, C.March 2013, Journal of Metabolism, pp. 400-410.
  20. Physiological Aspects of Male Libido Enhanced by Standardized Trigonella foenum?graecum Extract and Mineral Formulation. Steels, A.9, 2011, Phytotherapy Research, Vol. 25, pp. 1294-1300.
  21. Zinc status and serum testosterone levels of healthy adults. Prasad, A.5, 1996, Journal of Nutrition, Vol. 12.
  22. Association of vitamin D status with serum androgen levels in men. Wehr, E.2, August 2010, Clinical Journal of Endocrinology, Vol. 73, pp. 243-248.
  23. The role and molecular mechanism of D-aspartic acid in the release and synthesis of LH and testosterone in humans and rats. Topo, E.2009, Reproductive Biology & Endocrinology.