Testosterone is a anabolic steroid hormone. It is is the primary male sex hormone. It is an androgenic/anabolic steroid responsible for bringing about the maturation of the male sex organs (testes and prostate) during puberty.

It is androgenic in that promotes the development of testes and prostate during puberty as well as secondary male sex characteristics (deepening of the voice and growth of body hair). It is anabolic in that it stimulates skeletal muscle and bone growth.

Testosterone also helps promote fat lipolysis (mobilization and breakdown), control blood sugar, regulate cholesterol, and maintain a healthy immune system. It even affects key functions of the brain.

The vast majority (more than 95%) of testosterone is manufactured by the Leydig’s cells in the testes at various amounts throughout a male’s life. The other 5% is produced by the adrenal glands. Testosterone production peaks during puberty and then declines with age following puberty.

This natural decline in testosterone production leads to the prevalence of low testosterone in middle-aged and older-aged men. It is estimated that between 20-40% of older men have low testosterone and/or suffer from symptoms associated with low testosterone.

Testosterone can either be bound or free in the bloodstream. Most testosterone (>98%) is bound. Less than 2% of total circulating testosterone is free. When bound, testosterone is not biologically active. That is, it cannot exert its effects.

As mentioned above, the testes produce testosterone. After the testes produce it, testosterone enters and circulates through the bloodstream, so that it is available for tissue uptake. As it circulates through the bloodstream, it is typically bound to a carrier protein. The carrier protein helps it move through the bloodstream and safeguards it from being eliminated by the body too quickly. Once testosterone enters the tissue, the carrier protein dissociates. The two primary carrier proteins that transport testosterone are sex hormone binding globulin (SHBG) and albumin. Most circulating testosterone is bound to either SHBG or albumin. Typically, only about 2% exists in the free, unbound state.

Blood tests to measure testosterone levels will report a total testosterone level as well as a free testosterone level. Your free testosterone level is as important, if not more important, as the total testosterone level because free testosterone is the only biologically active form of testosterone. It is not uncommon for total testosterone levels to be normal and free testosterone levels to be low or vice versa.

he normal range for free testosterone in men is 5 ng/dL to 21 ng/dL. It should be noted that labs use different assays and methodologies to measure free testosterone levels. A free testosterone (direct) test will yield values outside of the above range if you try to convert the values. Compare your lab results directly to the lab provided range to assess where you stand. For example, AnyLabTestNow provides a free (direct ) range of 35 to 155 pg/mL (3.5 to 15.5 ng/dL).

Two important points should be noted regarding the normal range for total and free testosterone levels. The first point concerns the size of the range and the second point concerns the fact that testosterone levels naturally decline with age. Therefore, the prevalence of low testosterone is far higher in older populations, and men with normal testosterone now may experience symptoms of low testosterone later in life.

First, the normal range for total and free testosterone levels is quite large. One man can have nearly three to four times the testosterone as another man and both men can be considered “normal”. The change in testosterone levels over a lifetime can be just as important as the actual clinical value for the presentation of symptoms. While low testosterone is generally defined as total testosterone below 300 ng/dL, men with levels above this cutoff value may experience symptoms of low testosterone because of the their individual change in testosterone levels.

Some men start to experience the symptoms of low testosterone at merely low-normal levels; anecdotal reports include some men suffering symptoms of low testosterone at levels as high as 450 ng/dL. Consequently, physicians typically consider the diagnosis of low testosterone and the subsequent decision to pursue testosterone replacement therapy on an individual basis by considering an individual’s age, symptoms, health, and testosterone levels.

Second, testosterone levels naturally decline with age. Total testosterone levels decline nearly 30% between the ages of 25 and 75. Free testosterone levels decline nearly 50% between the ages of 25 and 75. This natural decline is the major reason for the increasing prevalence of low testosterone in older men.

Talk to your doctor about these symptoms. Your doctor can perform simple blood tests to determine whether your testosterone levels are low or not. Only a blood test can definitively determine whether your testosterone levels are low or not.

To determine your testosterone levels, physicians will request a blood test. This blood test will measure your total testosterone level. It may also measure your free testosterone and SHBG levels. Any test providing all three values will provide more information than the total testosterone level alone. The test requires a blood sample to be taken from a vein. The best time for the blood sample to be taken is between 7 a.m. and 10 a.m because testosterone levels fluctuate throughout the day. A second sample is often needed to confirm a result that is lower than expected.

If you suspect you have low testosterone, start by talking about these symptoms with your doctor. Then, ask your doctor for a simple blood test to measure your testosterone levels. If you’re doctor won’t perform a blood test, either get a different doctor or get some blood work done yourself. Plenty of companies now offer hormone panel testing services, Any Lab Test Now, DirectLabs, DiscountedLabs, ZRT Laboratory. While you can’t get a TRT prescription from them, you can arm yourself with the results by figuring out whether or not your levels are low.

Below is a good starter list of values to get tested

Total Testosterone Bioavailable testosterone (aka Free and Loosely Bound) Free Testosterone SHBG DHT Estradiol (specify “sensitive” assay for males) LH FSH Prolactin Cortisol Thyroid Panel (complete) PSA ( age dependent) CBC Comprehensive Metabolic Panel Lipid Panel Vitamin D

In addition to measuring your total testosterone and free testosterone, measuring your LH (luteinizing hormone), FSH (follicle stimulating hormone), prolactin, and thyroid function may provide useful information for understanding the potential underlying cause of low testosterone. To understand why these values are useful, it is helpful to understand the difference between primary and secondary hypogonadism (low testosterone) and how testosterone is produced and regulated in the body.

There are two basic types of low testosterone (hypogonadism): primary and secondary hypogonadism.


What is TRT? Testosterone replacement therapy (TRT) is the administration of testosterone to men to treat low testosterone. The main goal of TRT is to reestablish normal testosterone levels. Physicians typically aim to reestablish a testosterone level between 500 ng/dL and 1000 dg/nL. All testosterone preparations detailed below require a prescription and are FDA-approved for low testosterone.

Men sometimes confuse anabolic steroid usage (testosterone cycles) for the purpose of bodybuilding with testosterone replacement therapy. TRT uses normal, physiological dosages to increase low testosterone levels back to normal levels. The testosterone preparation is taken regularly, oftentimes for the rest of an individual’s life. On the other hand, testosterone cycles for the purpose of bodybuilding use above normal, supraphysiological dosages to increase testosterone levels above normal for a period of time. Users of testosterone cycles for the purpose of bodybuilding cycle on and off testosterone to give their bodies a break from these supraphysiological testosterone levels.

Testosterone can be converted in estrogen via the aromatase enzyme. Consequently, taking testosterone via TRT may increase estradiol levels. Most men on TRT dosages will not experience high estradiol levels. However, some genetically susceptible men may experience high levels. These high estradiol levels may lead to feminizing effects such as fluid retention and gynecomastia. As such, it is important to routinely test estradiol levels during TRT.

Testosterone replacement therapy in men with low testosterone produces many positive benefits. These benefits can be broken down into conclusive benefits and inconclusive benefits. Conclusive benefits are benefits that are relatively certain, whereas inconclusive benefits are benefits that are not certain.

Conclusive Benefits: Testosterone replacement therapy has consistently shown to positively alter body composition. It increases muscle mass (via increased muscle synthesis) and decreases fat mass (via increased fat lipolysis), especially abdominal fat mass. It also slows or even reverses the loss of bone mineral density due to aging. TRT also increases libido.

Inconclusive Benefits: Testosterone replacement therapy may also improve sexual function (improve erectile function), improve mood, reduce depression. However, TRT has not been shown to conclusively improve erectile function and mood. The primary reason why TRT may not help with erectile dysfunction or mood/depression is because both conditions can be related to one or more of many potential underlying medical conditions unrelated to testosterone levels. Without addressing such underlying conditions, testosterone alone will likely not improve erectile dysfunction or mood/depression.

Oftentimes, testosterone levels can be increased by simple, healthy lifestyle modifications. If your testosterone levels are low, before beginning any TRT, it is important to address any poor lifestyle choices that are detrimental to the therapy.

What boosts testosterone production?

Lifting weights, especially heavy weights - Weight lifting increases testosterone production. Performing big, basic exercises with heavy weights increases testosterone the most. Heavy compound exercises like the bench press, barbell row, military press, straight bar curl, close-grip press, squat, and deadlift are ideal for promoting testosterone release.

Getting good, quality sleep – The majority of testosterone release occurs during sleep, and the body releases far more testosterone when sleep is better and longer (7-8 hrs). Anything that reduces the quality and duration of sleep, such as alcohol, caffeine, sleep apnea, or even certain medications will decrease testosterone release

Getting proper rest in between workouts – While weight lifting helps to boost testosterone levels, too much training can actually lower testosterone levels. Over training causes cortisol levels to rise, which counters testosterone.

Eating healthy – Certain foods help boost testosterone release, while certain foods lower testosterone release. Sugars and unhealthy fats (saturated and trans-fats) lower testosterone production. On the other hand, healthy fats like unsaturated and polyunsaturated fats help increase testosterone production.

Staying lean – Testosterone levels are significantly lower in obese men than levels in their leaner counterparts. Stay lean by getting an adequate amount of aerobic and resistance exercise and eating healthy.


It it responsible for promoting increased muscle mass, strength, bone mass, and decreased fat mass. Testosterone also plays an important role in a man's sex drive a mood.

Normal total testosterone levels range from approximately 300 to 1050 ng/dL. There is no absolute consensus among different medical organizations for the exact cutoff for low testosterone. In general, the cutoff ranges from high 200s to low-to-mid 300s ng/dL.

As men age, testosterone levels decline. As a result, many men have low testosterone and/or experience symptoms of low testosterone. Low testosterone symptoms include a loss of muscle and gain in fat mass, reduced energy and sexual desire, erectile dysfunction, and depression.

Low testosterone is treated with testosterone replacement therapy (TRT). TRT is the administration of FDA-approved, prescription testosterone preparations. The goal is to raise testosterone levels back to normal levels (between 500 ng/mL and 1000 ng/mL).

Common testosterone preparations include gels and creams, injections, lozenges, and implantable pellets.


1   Function

Testosterone is the principle male sex hormone.

1.1   Aggressiveness

Via reddit comments on https://www.reddit.com/r/science/comments/basuvr/testosterone_increased_leading_up_to_skydiving/:

The stereotype of the aggressive male body builder, is possibly due to aromatizing of excess testosterone into Estrogen. Except bodybuilders take Aromatase Inhibitors which stop the aromatization

“Roid rage” is a real thing, however it’s cause has been greatly misunderstood. It is not a result of high testosterone, but it is instead a result of the heightened estrogen levels that accompany an increase in testosterone. When woman have periods, their estrogen levels spike temporarily, and they also start exhibiting much of those same “roid rage” characteristics. And of course, high estrogen levels effect people differently. Some are not effected at all, but most are.

Aromatase doesn’t produce anything. It’s simply an enzyme that converts testosterone to estrogen. And you’re totally right about testosterone leading to patience and stuff like that. Testosterone is actually associated with reduced anxiety and anti-depression effects. The “roid rage” people talk about usually comes from people injecting it for performance-enhancing reasons and the rage actually comes from when they don’t inject. Like in between their cycles of testosterone they get angry and super anxious.

Aggression factor is related more to DHT, which can also increase feelings of mistrust supposedly. Also the cause of male pattern baldness. No, it’s the fuel of male pattern baldness. The genes of MPB are the cause. If you don’t have the MPB genes then you can have extremely high DHT with no effects on your hairline.

Popular scientific literature, art, and the media have been attributing the roll of aggression to the arguably best known sexual hormone for decades. Research appeared to confirm this -- the castration of male rodents evidently led to a reduction in combativeness among the animals. The prejudice thus grew over decades that testosterone causes aggressive, risky, and egocentric behavior. The inference from these experiments with animals that testosterone produces the same effects in humans has proven to be false, however, as a combined study by neuroscientist Christoph Eisenegger and economist Ernst Fehr, both of the University of Zurich, and economist Michael Naef of Royal Holloway in London demonstrates.

For the study, published in the journal Nature, some 120 test subjects took part in a behavioral experiment where the distribution of a real amount of money was decided. The rules allowed both fair and unfair offers. The negotiating partner could subsequently accept or decline the offer. The fairer the offer, the less probable a refusal by the negotiating partner. If no agreement was reached, neither party earned anything.

Before the game the test subjects were administered either a dose of 0.5 mg testosterone or a corresponding placebo. "If one were to believe the common opinion, we would expect subjects who received testosterone to adopt aggressive, egocentric, and risky strategies -- regardless of the possibly negative consequences on the negotiation process," Eisenegger elucidates.

The study's results, however, contradict this view sharply. Test subjects with an artificially enhanced testosterone level generally made better, fairer offers than those who received placebos, thus reducing the risk of a rejection of their offer to a minimum. "The preconception that testosterone only causes aggressive or egoistic behavior in humans is thus clearly refuted," sums up Eisenegger. Instead, the findings suggest that the hormone increases the sensitivity for status. For animal species with relatively simple social systems, an increased awareness for status may express itself in aggressiveness

Moreover the study shows that the popular wisdom that the hormone causes aggression is apparently deeply entrenched: those test subjects who believed they had received the testosterone compound and not the placebo stood out with their conspicuously unfair offers. It is possible that these persons exploited the popular wisdom to legitimate their unfair actions.

Journal reference: Eisenegger et al. Prejudice and truth about the effect of testosterone on human bargaining behaviour. Nature, 2009; DOI: 10.1038/nature08711

University of Zurich. "Testosterone does not induce aggression, study shows." ScienceDaily. ScienceDaily, 9 December 2009. https://www.sciencedaily.com/releases/2009/12/091208132241.htm

Follow up study:

Eisenegger et al. The role of testosterone in social interaction https://www.sciencedirect.com/science/article/pii/S1364661311000787

2   Production

Testosterone is produced primarily in the testicles of males and the ovaries of females.

A doctor can check for low testosterone. They'll prescribe either androgel or shots. Shots are more convenient and cheaper.

2.1   Conversion to estrogen

Excess testosterone is converted to estrogen, but this can be prevent with a aromatase inhibitor, e.g. anastrozole (arimidex), Formestane.

2.2   Causes

  • Socially submissive males have less testosterone than dominant ones do. The apparent direction of causality is that low status causes low testosterone as (1) mating opportunities will be less frequent and (2) and aggressive demeanor is more costly if it can't be backed up. Speculating, it's possible that the lack of competition drops testosterone.


  • A 4-point increase in your body mass index (about 30 extra pounds on a 5'10" guy) can accelerate age-related T decline by 10 years.
  • Finnish researchers recently found that men who lifted weights regularly experienced a 49 percent boost in their free testosterone levels. "As you strengthen your muscles, the amount of testosterone your body produces increases," says David Zava, Ph.D., CEO of ZRT Laboratory. You need to push iron only twice a week to see the benefit.
  • A study published in the International Journal of Sports Medicine reveals that men who consumed the most fat also had the highest T levels.
  • In a recent Dutch study, men who drank moderate amounts of alcohol daily for 3 weeks experienced a 7 percent decrease in their testosterone levels.
  • Mental or physical stress can quickly depress your T levels. Stress causes cortisol to surge, which "suppresses the body's ability to make testosterone and utilize it within tissues," says Zava. Cardio can be a great tension tamer, unless you overdo it.

Research cited in Qaadri's book found that men who ate diets rich in monounsaturated fat -- the kind found in almonds -- had the highest testosterone levels.

2.3   Effects

The lack of testosterone causes the following: malaise, sleep problems, weight gain loss of muscle, low libido, and low energy.

3   Further reading

4   References

[1]Testosterone Week: How I Doubled My Testosterone Levels Naturally and You Can Too. http://www.artofmanliness.com/2013/01/18/how-to-increase-testosterone-naturally/
[2]Testosterone. http://examine.com/topics/Testosterone/
[3](1, 2) Jacob Davidson. Aug 26, 2013. Chopping Wood a Manlier Feel than Sports. http://newsfeed.time.com/2013/08/26/chopping-wood-a-manlier-feel-than-sports/

Diet/Exercise/Sleep. Getting plenty of fat, including saturated fat, as well as dietary cholesterol (read: eggs, whole fat dairy products, nuts) can help. Also, being in a calorie surplus helps.

Eat vitamin D, zinc and magnesium

Don't have a high bodyfat

Eat fatty foods (ex. avocados, eggs and olive oil)

Researchers from the University of California, Santa Barbara have discovered that chopping wood significantly increases testosterone levels, even more so than competitive activities. [3]

Scientists have known for a while that competitive exercise, like sports, tend to increase how much testosterone the body releases. The study, published in Evolution & Human Behavior, sought to determine how non-competitive exercise — like food production — compared. In order to do so, researchers tested the testosterone levels of the indigenous Tsimane people in central Bolivia before and after they cut down trees. Their results showed a 46.8 percent increase in testosterone levels following the wood cutting, a full 17 percent higher than the testosterone bump caused by playing soccer. [3]

Evolutionary biologists theorise that baldness is actually a sign of dominance, longevity, and social status due to its cause – a more potent form of testosterone called DHT.

Connected to Vitamin D?