TESTOSTERONE.
The literature describes Testosterone as a key anabolic hormones, serving as a chemical messenger to promote the growth of tissues. Alternatively, testosterone is like your over-eager friend that always wants the most out of life. They’ll push you beyond your physical boundaries in the pursuit of greatness but without restraint can land you in all kinds of trouble.
As such, testosterone optimisation is a major factor for everyone, particularly when applied to aspects of physical performance.
While testosterone is roughly 15x more prevalent in males, it is important to understand it is still one of the most abundant sex hormones in females and therefore plays a crucial role in sex drive, bone and muscle strength and regulation of the menstrual cycle.
So, let’s talk performance: how does testosterone increase athletic (or human) performance?
There are two avenues we can explore here:
1. the advantages of restoring low (or even normal) level testosterone to optimal levels;
2. the advantages of taking agents such as anabolic steroids to achieve supraphysiologic levels.
This article will focus on the first option to highlight several key components of performance and how testosterone affects them. Each component is divided into its own section so you can read those that are most pertinent.
effects on the body
STRENGTH
Strength is one of the pillars of human performance, directly or indirectly benefiting almost all functions of the human body. To emphasise just how significant the impact of strength can be, a study conducted with over 1 million Swedish adolescents found that, in this age bracket, high muscle strength was associated with a 20-25% lower risk of dying by any cause before 55[1]. This perspective was supplemented by a meta-review that concluded strength was a strong predictor of mortality[2]. The bottom line? Strength is really, really important for general performance, athletic or otherwise.
Now that we know that strength is a positive asset, how can we improve it? Put simply, there are two main ways we can make our bodies stronger: make the muscles bigger (hypertrophy) or get more out of the muscles we already have (via neural adaptations). To varying extents, testosterone has been shown to positively influence both of them.
1. Hypertrophy - A direct result of heightened testosterone is a net increase in proteins synthesis which promotes the growth of muscle cells. Epidemiological studies in this context are a bit dull as they only really give us an understanding of the connection between testosterone and lean body mass but fail to stress how significant this effect can be. To paint a clearer picture, let’s take a look at two randomised group studies:
I. A study on Hypogonadal (clinically low testosterone) men reported an average gain of ~4.5kgs by weight or ~10% by size (measuring cross sectional area of triceps and quadriceps) over a 10 week period when testosterone levels were restored to their physiologic levels[3]. These results were amplified by the fact that participants were instructed not to undertake any weight-lifting or moderate to heavy endurance exercise during this period.
II. Another study by Ronnestad et al. (1996) found similar results in young healthy men despite being administered 6x the testosterone[4]. The study compared the intervention of intramuscular testosterone against a control group with and without exercise for changes in body composition, muscular size and strength. Unsurprisingly, the most significant changes were witnessed in the testosterone with exercise group, where subjects saw a ~14% increase in muscle size (measured once again at the triceps and quadriceps) and ~10% increase in lean body weight within a 10 week period.
As we can see, both studies reveal the positive impact of testosterone on muscle growth by examining distinct test groups. Interestingly, the data from study (1) confirms the value of testosterone on people with low levels and in isolation (no exercise) while study (2) goes a step further to show how testosterone can supplement people with healthy levels and regular exercise.
2. Neural Adaptations - This effect is perhaps the least understood or defined by the current literature on testosterone. It is reasonable to suggest, however, that a large portion of the physical (strength) benefits derived from testosterone could be attributed to adaptations in the nervous system, provided changes in the nervous system account for the majority of strength gains made in the initial phases of a training program[5] [6]. A leading sports physiologist and researcher, the late Carmelo Bosco, proposed two methods by which this effect could take place:
I. In the short-term--defined here as the hours or minutes leading up to performance--circulating testosterone is likened to a heightened state of aggressiveness/ alertness which in turn increase the mobilisation of neuromuscular capacity. In simpler terms, this means testosterone could have a positive effect on both the speed (reaction time) and degree (strength/ power) of nerve firing.
II. In the long-term--meaning days or even years--it was argued that testosterone produced structural changes in the neurons that enhanced their capacity to act on their target muscles. In lieu of supporting evidence, Bosco extrapolated from the testosterone-fuelled sexual dimorphism that occurs in our formative years and derived implications from a combination of human and rat studies. Together, these changes increase the body’s ability to generate power by recruiting more of the muscles that are available instead of building more muscle tissue. This phenomenon is particularly useful to athletes or anyone who desires an increase in strength without putting on excess muscle.
Additionally, several studies have correlated restoring testosterone to their physiologic levels with an increase in muscle strength irrespective of hypertrophy. Auyeung et. al (2011), found that testosterone in older men had a favourable effect on muscle strength and physical performance which was independent of muscle size[7]. Ronnestad et. al (2011), found that the acute spike of testosterone in circulation following a heavy leg press actually improved 1rm arm curls by ~7% in the same session[8]. To reiterate, that is an almost 10% increase in strength in a matter of hours due to the testosterone increase from heavy lifting. So you want to get stronger faster? Time you get those neurons firing.
BODY COMPOSITION
The claim that testosterone levels are inversely proportional to body fat and/or positively influence the composition of our bodies has been investigated and supported more for men than women:
IN MEN, there is an abundance of research supporting the idea that higher testosterone levels, both physiologic and super-physiologic, have a positive impact on body composition. This includes decreases in subcutaneous (under the skin) and visceral fat (around your organs). And increases in muscle mass (lean body mass) and bone mineral density (BMD). Even the sexual dimorphism between skeletal systems is attributed, at least in part, to the increased levels of androgens (such as testosterone) in men[9]. Always wanted to look like a triangle...nice broad shoulders and a slim waist? Well, testosterone just might be your saviour. Admittedly, if you’ve already had your pubescent growth spurts the more profound effects will likely be centred around changes in fat and muscle bulk.
IN WOMEN, the literature is less certain. A study conducted on 329 postmenopausal women found that higher testosterone levels were correlated with an increase in lean body mass, strength and bone mineral density[10]. Conversely, a study of over 500 women between the ages of 27 and 47 showed a correlation between higher testosterone levels and increased body fat and waist circumference[11]. While both studies provide reasonable explanations for why their results are so contrasting, the reality is there is an insufficient body of evidence to make definitive claims in either direction. In lieu of sufficient supporting literature, our understanding of the underlying biochemistry (discussed under metabolic factors) would lead to the conclusion that testosterone would have a similar, albeit less significant, effect on women as it does on men. Results from a study of the relationship between elite female athletes and Polycystic Ovary Syndrome (PCOS), a condition characterised by heightened testosterone in women, lends support to this claim. Athletes with PCOS were found to have more muscle mass, a higher bone mineral density and an uptick in physical performance markers compared to other elite athletes[12]. This is to say, where all else was supposedly equal, the impact of higher testosterone on physiological outcomes was consistent for women and men.
FAST TWITCH FIBRES
The predominance of fast-twitch fibres in muscle composition can be advantageous for several reasons. Not only is the peak power output of fast-twitch fibres 4x greater than that of slow-twitch fibres but fast-twitch fibres also contributed 2.5x more than slow-twitch fibres to the total power exerted during various resistance exercises6. Additionally, these fibres have aesthetic merit as fast-twitch fibres have a thicker cross-sectional diameter making the muscle bellies thicker. The rationale behind correlating testosterone with the predominance of fast-twitch fibres is easily visible during the pubertal period which induces the physical disparity between the sexes. This stage is marked by, and in part attributed to, a dramatic increase in male testosterone. Furthermore, biopsy samples of adult muscles (the Vastus Lateralis) reveal women have ~30% more slow-twitch fibres, accounting for ~41% of their total muscle composition, while men have ~13% more fast-twitch fibres, accounting for ~66% of their total muscle composition[13].
SIDE NOTE
The predominance of slow-twitch fibres in women has been associated with a higher threshold for fatigue and provides a potential explanation for the lack of disparity between men and women in endurance events. One notable example is ultra-marathon runner Courtney Dauwalter who won a 240 mile race, thrashing her male and female competition by over 10 hours.
The above hypothesis is supported by an older rat study which found that the removal of testosterone by castration reduced the proportion of fast-twitch fibres in male rats[14]. When rats were administered a relatively large dose of testosterone, the impact on fast-twitch fibres was reversed. Admittedly, studies in humans isolating testosterone as an intervention have found that while testosterone does influence muscle growth, it does not make a preference between the various fibre-types[15]. While this doesn’t necessarily refute the hypothesis, it certainly draws attention to the need for further studies to be conducted. I suspect testosterone does influence the fibre make-up of our muscles but the degree to which it does so is heavily contingent on the training stimuli. For instance, power based, explosive sports are reasonably associated with the predominance of fast-twitch fibres and endurance sports are associated with slow-twitch fibres.
BONE
There are two proposed mechanisms by which testosterone directly influences bone growth and consequent health:
1. Longitudinal Growth (I.E. getting taller) - This effect is only notable during stages of growth such as puberty. However, a ray of hope exists for shorter people as studies on rats have correlated testosterone with the promotion of bone growth. One such study injected testosterone directly into the growth plates reporting increases up to 15%[16]. Although the results showed an increase in bone width and not length, testosterone related research might hold the answers to promoting growth and eradicating those pesky napoleon complexes.
2. Bone Mineral Density (BMD) - While people often visualise bone as this fixed scaffolding that slowly deteriorates over time, the reality is that our bones are in a constant flux as they break down and build back up. To elaborate, our bones are comprised of roughly 70% Calcium and Phosphorus (bone minerals), with the remaining 30% being organic matter such as Collagen. Unsurprisingly, changes in the composition of our bones can alter their quality, increasing the risk of becoming too rigid, porous, weak, less dense or even less flexible. Sex hormones (like testosterone) have been shown to promote the “building” component and decrease the “breaking down” component9. To give an appreciation for how profound this relationship is, the more than 1% per year decline in BMD seen in women (in their later reproductive years) is directly associated with lower concentrations of free testosterone[17]. For men, the picture isn’t any prettier as those with low testosterone levels have significantly lower bone density, particularly at sites such as the spine9.
So, why care about strong bones? For starters, they give shape to our body and protect the vulnerable underlying organs. They also serve as a reservoir for Calcium and Phosphorus, minerals that the body is in constant demand of for things like muscle contractions and nerve signalling. Bone health is of such importance that low BMD and the consequent fractures that are associated with low BMD are both highly correlated with an increased chance of all cause mortality[18] [19]. Additionally, there is still some debate as to whether these effects on bone are a direct or indirect result of testosterone via its conversion into estradiol (discussed later).
metabolic effects
PROTEIN SYNTHESIS
As we have established, testosterone is positively correlated with an increase in protein synthesis. This is supported by Ferrando et. al (1998) who reported a twofold increase in protein synthesis in individuals supplementing with intramuscular testosterone despite protein breakdown remaining unchanged15. This net increase in protein balance is the driver behind anabolic growth and consequent larger muscle. To add to this, an old yet sophisticated study on 6 young men supported this metabolic effect of testosterone by chemically inducing hypogonadism (clinical low-test) over a 10 week period. Blood samples of these test subjects revealed a “remarkable” decrease in the rate of appearance of the amino acid Lucine (which was used to determine how much protein was being broken down into its smaller constituents of peptides/ amino acids) and an overall decrease in whole body protein synthesis[20]. Together, the decrease in these markers in response to low testosterone indicates a net catabolic state. Moreover, this study went on to report a significant decrease in lipid oxidation (burning of fat) and increase in overall adiposity (fat gain), further affirming the aforementioned relationship between testosterone and body fat.
FAT CELLS (aka ADIPOCYTES)
As we already know a little about the propensity of testosterone to metabolise (break down) adipocytes, we should see how deep this apprehension towards body fat goes. Testosterone and its derivative DHT (discussed later) have been shown to influence the development of new cells, favouring a muscular (myogenesis) rather than fat (adipogenesis) path[21].
So not only does testosterone help break down fat but it can prevent it from accumulating to begin with.
To further define the inverse relationship between fat cells and testosterone, an increase in adipose tissue (fat) is associated with an increase in the aromatase enzyme which converts testosterone into estradiol[22]. As a result, an increase in fat can lead to a decrease in testosterone that perpetuates additional fat gain in what can best be described as a positive feedback loop that ain’t so positive.
INFLAMMATION
You’ve probably heard by now that inflammation is the devil. While it is certainly more complicated as many inflammatory processes are integral for life (such as recovering from an injury or a gruelling training session), it is pretty clear that the excess inflammation ubiquitous with our typical lifestyles is attributed to a plethora of negative health outcomes. The mechanism by which testosterone is anti-inflammatory is multifaceted but is largely attributed to its effect on adipocytes (fat cells).
A number of studies have acknowledged adipocytes for their role as endocrine tissues. These adipocytes are capable of secreting over 600 signalling proteins (known as Adipokines) to coordinate a variety of biological processes both locally and systemically[23] [24]. The nuance surrounding each adipokine remains ambiguous but we can appreciate that several key players in the promotion of inflammation continue to be illuminated as in the case of obesity which results in an excess secretion of these pro-inflammatory adipokines. This in turn causes a cascade of negative health outcomes that can ultimately contribute to a spectrum of obesity-associated disorders.
Another method in which testosterone is anti-inflammatory relates to C-reactive proteins (CRP) which play several important roles in the inflammatory process, becoming over 1000x more prevalent at sites of inflammation or infection[25]. While its function is essential, its excessive presence has been noted in an array of conditions from arthritus to infections. This relationship is so strong that CRP measures are used as a predictive marker for Cardiovascular Disease. Detailed in the literature review by Bianchi (2018), testosterone via its effects on insulin (discussed below), reduces the livers synthesis of CRP and therefore has an anti-inflammatory effect[26]. So while inflammation isn’t inherently negative, testosterone can mitigate the ramifications of excessive inflammation.
INSULIN
The importance of insulin is related to its role regulating blood sugar levels and trafficking nutrients around the body. Conversely, there is a host of evidence supporting the inverse relationship between testosterone and insulin resistance (as seen in type II diabetes). As both low testosterone and high insulin resistance can be symptoms of the same condition (such as obesity), it is important to establish a clear mechanism of action. Dwyer et. al (2005) proposes several[27]:
· Reduction in circulating free fatty acids that interfere with insulin signal transduction;
· Increase in AMPK expression and phosphorylation which increases the expression of GLUT-4, thus, potentially increasing glucose (sugar) transport;
· Suppression of previously discussed Adipokines and other inflammatory markers that interfere with insulin signalling.
These mechanisms have been supported by studies using testosterone as an intervention. The most promising of these findings has been on obese, insulin-resistant men in which the sample group took several weeks to note a significant effect. This could support the idea that improvements in insulin sensitivity were more impacted by the reduction in adipose tissue (fat) as opposed to the acute effects of testosterone. As we already know testosterone’s profound effect on adipose tissue, to the test subject, the result is the same.
VASCULAR SYSTEM/ BLOOD
The connection between testosterone, blood and the vascular system is complicated and often contradictory. On one hand, this interaction induces changes that could be perceived to enhance performance; on the other, it could be attributed to the sexual dimorphism associated with coronary artery disease and hypertension. Where performance is concerned, testosterone assists in the formation of new blood cells (erythropoiesis) while increasing circulating haemoglobin and the ratio of red blood cells to total volume of blood (haematocrit)[28] [29].
Consequently, these effects increase the blood’s capacity to carry oxygen, allowing an athlete to sustain a higher aerobic output for longer. This relationship is so well defined that not only has low testosterone been associated with anaemia (a condition defined by low haematocrit/haemoglobin) but before the advent of erythropoietin (aka EPO: historically, a personal fave on the Tour De France circuit), it was traditionally used as a treatment[30]. Unsurprisingly, too much of a good thing can cause problems and in this case excessive accumulation of red blood cells can contribute to high blood pressure.
Perpetuating the concern with erythrocytosis is testosterone’s effect on the vascular system. Through various pathways, testosterone has been shown to have a vasoconstricting effect that increases blood pressure[31]. This shines light on why men might have higher blood pressure than women. As the acute effects of testosterone are paradoxically vasodilatory, this effect only occurs in the long-term. While this is less of a concern for athletes or healthy individuals, it is worth considering for people with blood pressure complications or those planning to take supraphysiological doses of supplements that REALLY pack a punch.
effects on the brain
COGNITION
Several studies have investigated testosterone’s role in the brain and, by extension, its potential impact on cognition. Interestingly, results have been varied and include an improvement in verbal and non-verbal learning and memory in men of all ages; higher spatial performances in men and women with intermediate levels of testosterone; and in some cases, a failure to find any relationship at all[32]. The logic behind these investigations is based primarily on the presence of aromatase enzymes and androgen receptors concentrated in the Hippocampus and Amygdala (the regions of the brain involved in memory and learning). The aromatase enzyme acts similarly to alcohol in that it completely changes testosterone into something barely recognisable. It converts testosterone into a form of the predominately female hormone estrogen, known as estradiol. With regards to our ambitious friend testosterone, their motivational guidance is only useful if it has an audience to preach to. Androgen receptors are testosterones target audience, without them they are left floating aimlessly through our body and will never have a causal effect.
The idea is the presence of these enzymes and receptors implicate a use for testosterone in these specific branches of cognitive performance. Additionally, connections between low levels of testosterone and impaired cognitive function have been observed. Disappointingly, however, the bulk of literature supporting this finding were conducted on older men in which depreciating testosterone and cognition are a given.
More definitive research has been conducted on testosterone’s neuroprotective role, in particular its function against the age-related cognitive decline seen in Alzheimer’s Disease (the most common form of Dementia). The two major makers for this disease are (1) the accumulation of neurotoxic proteins (β-amyloid plaque) which disrupt the communication between neurons as it coagulates around them; and (2) the abnormal binding/ accumulation (hyperphosphorylation) of proteins (tau) inside the neurons (known as Neurofibrillary Tangles)[33]. A study on live hippocampal neuron cultures concluded that testosterone had a significant and rapid protective effect against cell death when exposed to these plaques[34]. Furthermore, another cell-culture study by Grimm et. al (2016) reported testosterone alleviated the mitochondrial deficit created by the accumulation of β-amyloid plaques[35]. A similar positive effect of testosterone has been noted with regards to the prevention of Neurofibrillary Tangle formation in both animal and human models[36] [37]. In fact, the study conducted on humans went on to propose that the lower testosterone levels in women may serve as an explanation for the higher prevalence and steeper decline of Alzheimers seen in females.
The two markers of Alzheimer’s described are the same markers seen in cases of brain trauma (e.g. concussions experienced by athletes). Long-term studies on professional football players revealed an increase in the early development of the disease, suggesting that testosterone optimisation has wide spread application for all forms of brain deterioration/ damage[38].
Psychological Factors
DEPRESSION AND ANXIETY
Depression and other mental health disorders like anxiety are prevalent and on the rise. In Australia, women are almost 2x more likely to experience depression and/or anxiety in their lifetime and men are roughly 3x more likely to take their own lives[39]. The scientific push to comprehend the underlying mechanisms of these conditions has shed light on their complex, multifaceted nature. A problem faced by mental health advocates relates to the unique factors that cause depression in individuals. While testosterone is no panacea, there is a well defined association between low testosterone and depression that is more consistent in men than in women[40] [41]. While it must be acknowledged that correlation does not equal causation, there are several perspectives we can indulge:
1. testosterone as an intervention;
2. possible mechanisms of action; and
3. sex and age differences.
Perspective (1) is perhaps the most promising as these studies are typically conducted on individuals with clinically low testosterone, thus the low testosterone is likely contributing to the depressive symptoms. For men, testosterone therapy (restoring to normal levels) was strongly supported by a systemic review and meta-analysis of depression, particularly for older individuals and those with hypogonadism (clinically low test) or even HIV/AIDS[42]. For both men and women, testosterone therapy has been used to treat both anxiety and depression. However, studies conducted in this way have been incredibly dose dependent40 41. There also existed a parabolic curve relationship where testosterone relieved symptoms of anxiety at physiologic doses but when these doses increased up to supraphysiologic levels, testosterone actually perpetuated them.
In the case of perspective (2), the pathogenesis of depression is yet to be fully understood and as such it is difficult to identify the mechanisms of action associated with testosterone. McHenry et. al (2014) propose several mechanisms including testosterone’s effect on neurotransmitters such as Dopamine and Serotonin and intracellular signalling pathways as well as its action on particular areas of the brain like the Amygdala[43].
Finally, as per perspective (3), the very fact there is a discrepancy between sexes in both the incidence and presentation of depression/ anxiety implicates sex-hormones. This is furthered by the most notable sex-depression findings coinciding with key stages of life such as puberty and menopause[44] [45]. It has also been suggested that testosterone may also also play a role in the threshold for depression. A study by Shores et. al (1998) found men with clinically low testosterone took a shorter period of time to develop the condition in comparison to men with normal levels[46].
MOTIVATION/ DRIVE
As testosterone can enhance mood, it is a reasonable assumption that optimal testosterone levels could lead to better health outcomes. A similar concept was tested and supported by Cook and Beaven (2013) that measured the varying testosterone levels in elite female netball players over a four month period. They found a strong correlation between higher testosterone levels prior to a workout with increased self-selected workloads[47]. The implication being higher testosterone levels equipped athletes with the drive needed to excel.
When we begin to extrapolate these findings over an extended period of time it is not unreasonable to think testosterone could hold tangible authority over our successes. In the athletic arena, several associations have been made between higher testosterone levels and winning[48] [49]. While this is an exciting development, the bulk of supporting evidence relies on saliva samples taken after the competition . The fault here refers to the acute spike in testosterone following a victory, inferring the higher levels of the hormone are likely due to and not causing the victory. Specific investigations into testosterone as a predictive marker for sports outcomes is scarce and done on too small a scale to be of interest.
Attempts to confirm this trend in other non-athletic fields using success markers like financial risk-taking, assertiveness and social status have proven less convincing 49 [50]. In some cases, a clearer picture is made when these markers are better defined; for example, when aggression is refined to reactive aggression (aggression in response to stimuli), the findings become stronger[51]. In lieu of investigations into specific markers of social success, the idea has emerged that testosterone tends to motivate an individual to pursue or defend high social status. Referred to as ‘Dominance Behaviour,’ this phenomenon affords a certain flexibility to the scientific approach by understanding how testosterone reacts in social settings, provided each circumstance is unique.
So how about success in the bedroom? Unsurprisingly, the sex-hormone testosterone plays an integral role in regulating sexual desire and ability. However, there is a distinct lack of clarity in the scientific literature surrounding this topic. According to one review investigating testosterone as an intervention for sexual function and/or satisfaction, only 23 studies out of 47 reported any benefit[52]. One again, if we focus our search the connection between sex and testosterone becomes clearer.
Lets begin with a look at our libido (sex drive). Studies evaluating libido tend to rely heavily on questionnaires. The difficulty here refers to the fact there is no consensus on what questions are used and what answers are given, which I believe to be a chief explanation for the lack of consistency in the literature. Having said that, there remains an abundance of research to support the testosterone-libido relationship in both men and women as outlined in a 2017 review outlining the value of restoring testosterone levels to improve male libido[53]. This links to an older study that chemically castrated otherwise healthy individuals before comparing various levels of testosterone against a control group[54]. The placebo receiving control group reported “significant decreases in frequency of sexual desire and fantasies during the treatment period, along with decreased frequency of intercourse”. In other words, it was a catastrophe. For females the efficacy of testosterone is equally complex, appearing to be contingent on whether it is administered before or after menopause. According to a review by Reed et. al (2016), available evidence does not support the use of testosterone for low-libido in women, highlighting the need for further research[55]. Conversely, studies on postmenopausal women found supplemental testosterone to be both safe and effective[56] [57].
For both men and women alike, it seems likely that testosterone derived from improvements in health and fitness is ‘better’ than administered exogenous testosterone. In the context of libido, the naturally derived benefits may pack more of a punch.
Testosterone can help with the performance side of things too. For the ladies, the sequelae of impaired sexual desire, arousal, pleasure and overall satisfaction related to Female Sexual Dysfunction were shown to be improved with the use of testosterone[58]. These findings are consistent with those found in men in which a 2019 review coined testosterone a cornerstone of pharmacologic management. It concluded that testosterone replacement therapy (TRT) can ameliorate markers of Male Sexual Dysfunction, including low libido, erectile dysfunction and poor sexual satisfaction[59]. Finally, links between testosterone and the frequency and duration of orgasm is less definitive but has been shown to be more profound in women than in men[60].
Other Factors
SLEEP
The importance of sleep is worthy of its own article, but for the current purpose I will limit the discussion to its relationship with testosterone. In this regard, testosterone production is directly tied to our circadian rhythm (sleep pattern), indicating a link between optimal sleep and optimal testosterone levels (detailed under ‘less obvious stuff’). Perhaps less appreciated is the role of testosterone to promote sleep quality. A cursory look at the literature indicates an abundance of correlative studies connecting low-testosterone to impaired sleep; however, much like the ‘chicken and the egg’ scenario, it is difficult to discern what comes first. Studies, therefore, have primarily relied on a search criteria that isolates testosterone as the intervention. One such study on hypogonadal (clinically low-test) men reporting a significant reduction in sleep disturbance over a 12 month course of testosterone replacement therapy (TRT)[61]. This is supplemented by the findings of a previous experiment conducted on mice that sought to investigate sex-hormones to explain why women are over 40% more likely to experience insomnia[62]. Following a gonadectomy (ouch!), these mice experienced a reduction in both quality and quantity of non-REM sleep that was reversed when supplemented with testosterone[63].
Before all the insomniacs jump the gun, know that supraphysiological doses presented their own issues. The findings of another small study indicate high-dose TRT can disrupt sleep and breathing while reducing total time slept[64]. As a caveat, however, this study was conducted on older men and may not reflect the population as a whole, warranting the need for more research in this area.
MORTALITY
In light of previous evidence associating low testosterone with an increase in mortality and disease severity, a literature review by Muraleedharan & Jones (2014) correlated testosterone with an increased chance of dying by any cause[65]. Furthermore, a review by Corona et. al (2011) highlighted that a seemingly trivial decrease in testosterone was associated with a 35% increased risk of all-cause mortality and a 25% increased risk of cardiovascular mortality[66].
PRO-INFLAMMATORY CYTOKINES
The promotion of pro-inflammatory cytokines has been offered as an explanation for why the inverse relationship observed between testosterone and mortality exists. There are two ways to interpret this: 1) the same pathology that suppresses testosterone also promotes greater activation of pro-inflammatory cytokines (such as is the case in obesity); or 2) circulating testosterone down-regulates pro-inflammatory cytokines and/or up-regulates anti-inflammatory cytokines[67]. In lay terms, Inflammatory Cytokines are like your super confrontational friend. In certain instances, like when the waiter brings out the wrong meal, you actually appreciate their ability to speak up. For the most part though they seem to cause a scene for nothing. In instance 1, a condition like obesity drives you to spend less time with our friend testosterone, replacing them with your confrontational counterpart. In instance 2, our friend testosterone convinces inflammatory cytokines that they should chill-out a little and love thy enemy instead of turning everything into a fight.
In either case there is a net gain in the presence of pro-inflammatory cytokines which are considered to play a key role in the pathogenesis of disease. This theory is further supported by a recent literature review that found a significant association between low testosterone and high levels of inflammatory markers in a breadth of clinical conditions such as: Obesity, Heart Failure and type 2 diabetes[26].
“...I get it, testosterone is important. What now?”
the obvious stuff
EXERCISE
Not only does testosterone have a positive effect on many of the elements of exercise discussed above but exercise is an excellent way to promote testosterone production (talk about a positive feed-back loop!). These effects occur as both an acute response and long term adaptation to exercise:
The acute, non-genomic testosterone boost is harnessed within minutes of terminating exercise and lasts for several hours due to an excitement of androgen receptors in the muscle. Unsurprisingly, this effect is contingent on the difficulty of exercise as observed in a study comparing a biceps-only session with a biceps + legs session, noting the acute spike in testosterone following exclusively the latter[68]. This is one of several reasons I advocate full-body training.
Long-term, sustained spikes in testosterone have been shown in untrained individuals in as few as 5 weeks and in national-level weight lifters over a 2 year period[69] [70]. To provide perspective on the profound degree to which this effect takes place, a separate study determined similar results on young soccer players who reported an average of 7.5% increase in resting serum total testosterone over an 11 week period when undergoing a simple 2x per week strength training program[71].
SLEEP
Testosterone shares a close relationship with sleep, with levels appearing to be directly tied to our sleep pattern (circadian rhythm) and stages of sleep in an ultradian rhythm. Testosterone levels are highest upon waking and gradually decline over the course of the day, fluctuating as much as ~30%[72].Concentrations then restart their climb at the onset of sleep, however, this does not happen in a liner fashion. Secretions peak approximately once every 90 minutes, which falls in parallel with our REM sleep cycle[73]. The thought is not that REM sleep induces testosterone production, rather, REM sleep and testosterone synthesis may share the same neurophysiological state. The tangible effect of a bad nights sleep is reflected in our hormones almost immediately. To elaborate, Leproult & Cauter et. al (2011), reported a non-trivial 10-15% drop in daytime testosterone levels following a single week of restricted sleep (5hrs/ night)[74].
the less obvious stuff
While the following interventions can be done without a blood test, such a test will remove a considerable degree of guess work and reveal the areas in need of the most attention. This also allows a practitioner to oversee your progress if doubts remain. In general, those who respond best to dietary or supplemental strategies are those who have the most room for improvement/ are deficient.
NUTRITION
The use of observational studies featured heavily in nutritional sciences means that we can vaguely associate any intervention with a desired outcome. Instead of listing all the nutrients that are associated with higher testosterone, I will stick to those that have a clear mechanism of benefit.
Macronutrients
As an extreme overgeneralisation, people tend to undereat good quality fats and overeat carbohydrates. Both of these traits can detract from optimal testosterone levels for opposing reasons.
Fat - As cholesterol is the precursor to all steroid hormones, dietary fat is the chief macronutrient of concern as it pertains to testosterone. In fact Santos (2017), proposed dietary cholesterol, through the increased intake of fats, to be the driver behind the heightened testosterone seen on ketogenic diets[75]. Conversely, a 2021 systematic review and meta-analysis found low-fat diets to diminish testosterone by 10-15%[76]. Hardest hit were those following a vegetarian low-fat diet, with levels dropping my as much as 26%.
Carbohydrates - Excessive carbohydrate intake can desensitise our bodies to insulin. As a result, we can develop insulin resistance and if the trend continues, the body is well on its way to developing type II diabetes. This may sound dramatic but the prevalence of insulin resistance in various populations worldwide occurs lowest at 15.5% and highest at 51%[77] [78]. Insulin resistance means more insulin is required to do the same physiological job; therefore, insulin presence can lead to a decrease in testosterone levels. Now before you do away with all carbohydrates in your life, as with the Ketogenic Diet, understand that undereating carbs can be equally detrimental to testosterone. While much more evidence is needed to make a definitive claim, there appears to be a relation between keto-like diets and high SHBG levels (discussed below) which could lower free-testosterone.
Micronutrients
DHEA - DHEA/ DHEAS are hormones made from cholesterol that are precursors to the production of hormones such as testosterone or estrogen. As they are unspecified precursors, their effect on the body can be vast. In the periphery/ non-reproductive tissues such as our muscles, testosterone can be locally synthesised from reservoirs of DHEA and DHEA sulphate. As DHEA itself can be synthesised in the adrenals, speculation surrounds the necessity to supplement with it. The quick counter-argument is that DHEA levels are estimated to deplete by as much as 80% over a lifetime, starting around the age of 30[79]. On the other side, there is the argument that supplementation works. A 2020 meta-analysis of 42 publications demonstrated that testosterone levels were significantly increased after DHEA administration, the magnitude of increment being higher in females[80]. For athletes competing under tested organisations, know that DHEA is currently on WADA’s banned substance list.
Vitamin D - The presence of Vitamin D receptors and Vitamin D metabolising enzymes expressed in the male reproductive tract implicate the vitamin in the synthesis of male sex-hormones [125]. Yet despite this plausible mechanism of action, the literature isn’t as convincing. A 2021 systematic review and meta-analysis revealed a slight yet “just significant” association between the vitamin and the hormone[81]. Unsurprisingly, the review noted a more significant association in those who were deficient. This finding is consistent with a study by Pilz et. al (2011) that found Vitamin D to significantly increase testosterone in obese, deficient men when compared to a control group[82]. While Vitamin D status in Australian’s appears to be substantially better than those observed in other countries, sub-optimal levels are still reflected in 23% of our population[83]. As the most natural source of Vitamin D, the sun appears to have the most tangible effect on our hormones. A year long study on 2,299 men found time in the sun to increase testosterone by as much as 69%[84]. While this is a stand-alone study it certainly shows promise, particularly when it’s estimated that 90% of our vitamin D is obtained from time spent in the sun83. Remember too, like an elegant frame on a tasteful painting, a little tan could showcase the testosterone-fuelled masterpiece you’ve created.
Magnesium - In addition to the muscle performance and anti-inflammatory effects described by Maggio et. al (that could indirectly increase testosterone), magnesium has also been shown to directly increase bio-avaliable testosterone by increasing testosterones affinity to SHBG[85] [86].
Zinc - Zinc is the second most abundant trace mineral in the human body, known for its anti-inflammatory and anti-oxidant roles. It also plays an important role in testosterone concentrations. A study conducted by Prasad et. al (1996), that restricted dietary zinc intake for 20 weeks reported more than a 75% drop in testosterone levels that was, at least in part, reversed with zinc supplementation[87].
Boron - Boron has been shown to increase testosterone in both men and women, with postmenopausal women experiencing a more than two-fold increase after several weeks of supplementation[88]. Furthermore, Boron has been shown to share similar benefits as those described for testosterone including: bone health, lowering markers of inflammation and cognitive performance, in addition to improving vitamin D and magnesium levels[89]. For years Boron was not recommend by the TGA for consumption over concerns regarding heavy metal toxicity. Consistent with other countries, the TGA recently amended these recommendations and approved Boron for consumption.
HORMONES
Sex Hormone Binding-Globulin, aka SHBG
As the name suggests, SHBG is a protein produced in the liver that binds to hormones. In the context of testosterone, it acts as a transporter to escort approximately 65-70% of the testosterone in circulation[90]. Consequently, SHGB deactives testosterone, essentially rendering it useless (in the context of this article). As a result, ‘free testosterone’ is considered more valuable than total testosterone. In lay terms, this is akin to when testosterone settles down with their significant other and is no longer allowed to spend countless hours pushing your limits.
Like inflammation, SHBG performs an integral role in the body but in excess can be detrimental to health and testosterone. Several studies have actually proposed low testosterone and high SHBG as predictive markers for all-cause mortality[91]. To add fuel to the fire, the ratio of total testosterone to SHBG can decrease by as much as 50% over a lifetime[32]. For females, a lower SHBG level appears to be favourable in the athletic arena as 31% of elite athletes have hormone profiles consistent with PCOS, marked by normal total testosterone and low SHBG levels[92]. For reference, this same hormone profile is reflected in only 4-12% of the general population.
SYMPTOMS: Unsurprisingly, very similar to that of low testosterone:
Decreased sex drive/ sexual function
Decreased energy/ motivation
Reduced bone/ muscle mass
[93]
CAUSES of high SHBG:
Alcohol/ Smoking
Birth Control Pills/ High Estrogen Levels
Excessive Physical or Emotional Stress
Extreme Low Calorie/ Carbohydrate diets (this is debated)
Increases with age (in males and older women)
Vegetarian diets
Oral contraception
[93] [94] [95]
TREATMENT:
Boron
Magnesium
Saturated Fatty Acids
Fish Oil/ Polyunsaturated Fatty Acids
Vitamin D
Zinc
Tonkat Ali
More carbohydrates, particularly cruciferous vegetables (if carbohydrate intake is currently very low)
[93] [85] [75]
Estrogen
The presence of estrogen directly influences the synthesis of additional testosterone via Kisspeptin neurons found within the brain[96]. High levels of estrogen are interpreted by these neurons to regulate the secretion of gonadotropin-releasing hormones that reduce testosterone production. To complicate matters further, testosterone can be converted into a form of estrogen via an aromatose enzyme (estradiol) in which excess aromatisation and high estrogen levels can work to lower testosterone, consequently testosterone can serve as its own negative feedback mechanism[97].
It should be stated that estrogen or estradiol are integral to a number of healthy functions in the body. I think it is important to acknowledge, however, the sequela derived from these hormones in excess. Exacerbating this effect is the higher aromatase expression in adipocytes (fat cells), meaning the conversion of testosterone to estradiol is more prevalent in those with higher body fat[98]. Fortunately, for those in pursuit of higher testosterone, there are solutions.
TREATMENT:
Get leaner
Cruciferous vegetables like broccoli or cauliflower
Curcumin
Green Tea
Grape Seed Extract
[103] [104]
SYMPTOMS:
Increased Fat (particularly around abdominals or nipples)
Low Sex Drive
Lethargy/ Fatigue
Men
Infertility
Erectile Dysfunction
Women
Irregular Periods
Bloating
[99] [100] [101] [102]
Dihydrotestosterone (DHT)
DHT is the non-aromatisable form of testosterone and cannot be converted into estrogen. This hormone is involved in many vital roles throughout the body, including blood regulation, cognitive and sexual function as well as strength and muscle mass[105]. There are some undesirable androgenic effects that can emerge in relation to DHT but for many this may never be a concern. Actions to reduce DHT can be taken should symptoms begin to show; as it is an issue that is easily remedied, a strategy optimising testosterone should be prioritised.
TREATMENT:
Polyunsaturated Fatty Acids (PUFAs)
Vitamin B2
Curcumin
Green/ black tea
Fenugreek
Flaxseeds - although this seems to dramatically decrease testosterone too
[105] [107] [108]
SYMPTOMS:
Acne - particularly if this is in response to training
Irregular Hair-growth:
Baldness in men
Male-like hair growth in women
Prostate Cancer
Depression in women
[106]
SUPPLEMENTS
A few poorly understood supplements that have some scientific grounding.
Ashwagandha (aka Withania Somnifera) is a herbal medicine that has vast applications from neuroprotective roles in brain disorders to increasing the activity of immune cells[109] [110]. It is traditionally used for stress management by reducing cortisol but the herb also has a dramatic testosterone boosting effect[111].
Curcumin is an active phytochemical that accounts for roughly 2% of the makeup of turmeric and can be consumed via your diet. In terms of testosterone, curcumin may inhibit the conversion of testosterone into DHT (via the 5α-reductase enzyme) and the conversion into estradiol (via reduction of effects of aromatase enzyme)[112] [107].
Fenugreek improves insulin sensitivity, has significant impact on strength, body composition and endurance. But most importantly, it increases testosterone while decreasing DHT[113] [114].
Tongkat Ali (aka Eurycoma Longifolia) is a supplement that has been shown to increase testosterone, muscle and strength in addition to decreasing SHBG[115] [116]. Used acutely, it’s like rocket fuel for the bedroom, stimulating both desire and performance. Quality is a big issue so steer towards good quality extracts.
other lifestyle factors
Erotic Stimuli - Whether from pornography, a vivid imagination or whatever else gets the blood flowing down there, erotic stimuli has the capacity to spike testosterone in both men and women[117]. This is an acute effect that seemingly has no bearing on our long term levels and does not require any actual sexual act (sex or masturbation). The theory that abstinence peaks testosterone levels is based on a Chinese study that found testosterone peaked 7 days in, followed by no effect[118]. Attempts to support this finding have been unsuccessful despite clever wording exaggerating the data[119].
Alcohol - Unsurprisingly, alcohol is rough on our testosterone, intruding at the source of its production along with many steps throughout its synthesis. Alcohol’s war against testosterone can disrupt the HPG-Axis, dysregulate luteinising hormone and deplete essential nutrients[120]. These effects can lead to a cascade of issues that extend far beyond testosterone disruption. Additionally, alcohol could possibly enhance aromatisation (conversion into estrogen) and/or impair the metabolism (breakdown) of estrogen in the liver[121]. Interestingly, high testosterone may be associated with an inclination to consume higher amounts of alcohol.
Oral Contraceptives - In a review, women taking oral contraceptives were found to have lower levels of total testosterone, free testosterone and higher levels of SHBG[122]. Another study boasted similar findings with a significant increase in the SHBG and a “sharp reduction” in serum concentrations of free testosterone, total testosterone and DHEA’s[123].
Plastic - You’ve probably heard by now BPA isn’t ideal for testosterone but it turns out neither are the majority of plastics[124]. Detailed in her book ‘Count Down’, Dr. Swan brings to light the extreme consequences of Phthalates found in plastics to make them more durable. This includes drastic changes in fertility, male and female reproductive development and worst of all - low testosterone levels.
final word
Whether it be due to production, sensitivity, competition with other hormones, you name it -there is an incredible amount of subjectivity to our hormones. While the nuanced effects of testosterone on the various systems are debatable, the reality is that the steps taken to improve it tend to be the same steps required to improve other facets of life. In this regard, it is important to note that optimising testosterone levels is not the same as increasing it. Simply sky-rocketing your testosterone through a needle may contribute to an excellent physique but doing so could sacrifice other components of health, leading to a lot of failed potential. As it stands, testosterone is an integral piece of our overall health and with this article I hope to outline how it can be used to pursue health and fitness objectives
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