Tribulus is a herb used in China and India for many centuries, mainly for it’s libido enhancing properties and supposed testosterone boosting properties. It enhances testosterone levels by increasing luteinizing hormone (LH) levels. LH is responsible for “telling” the body to produce testosterone. This herb contains Dioscin, protodioscin, diosgenin. These three organic component stimulate sexual performance and may be useful for a variety of sexual disorders such as low testosterone, low sexual energy and weak erections.
The bogus products that have been draining your wallet and fattening the bank accounts of supplement companies are the so-called “natural testosterone boosters.” Billed as the saving grace to your low testosterone levels, poor body composition, and pitiful strength levels, natty test boosters were viewed by consumers as the answer to everything that was wrong.
I was age 55 with T level at150 so the va doctor started me out on bi weekly 200mg injections.Needless to say it really made me fell young again. My depression seemed to get better my sex life returned had lots of energy lost weight ect.Well i moved to upstate NY and the new doctor said that she was going to discontinue my treatments due to it being addictive drugs?I was in a va 6month rehab treatment for alcohol and opiate addictions.I went down hill very fast with my depression and my ability to focus & concentrate in my daliy functions.I went allmost a yr. before my new doctor found my levels being low and started me back on the injections 200 mg biweekly at the hospital va clinic but due to my addictions wont send me the needles for home use as before.So they gave me andro gel 1 pump daily but after my last visit she doubled the dose to 2 pumps daily and i am starting to feel and look better!I work out 5 days a week very hard in the weight room and have gained some great results in strength and muscle mass.She is going to check my blood work again in 2 months to see if it needs to increase my dose again.Any ways thanks for the best information i have seen so far o this subject.Also the TRT has given me my life back and i am so glad that this was here to help me as i grow old!
The other interesting thing about the study: men’s testosterone levels were lowest in March (at the end of winter) and highest in August (at the end of summer). Sunlight affects your vitamin D production, so you have seasonal dips and peaks. Get a blood test to check your levels, and if you’re low, take a high-quality vitamin D3 supplement. If you’re going to take D3, take vitamin K2 and vitamin A with it. The three work in sync, so you want them all to be balanced. Here are my dosage recommendations.
Consuming high amounts of sugary foods raises your blood glucose levels, which causes your body to release insulin as a response to the raised blood glucose levels. If not managed correctly, the body begins to develop a tolerance to insulin and cannot absorb the sugars in the blood stream as it used to, causing you to become insulin resistant. Being insulin resistant releases cortisol, and as you know, cortisol has extremely negative effects, lowering testosterone by quite a bit.
The all-new True Grit Test Booster is scientifically engineered to deliver the most powerful testosterone-boosting ingredients on the market today. This powerful 3-in-1 formula offers the benefits of both free and total testosterone boost as well as cortisol balance. Using powerful clinically studied key ingredients, True Grit Test Booster works with the body to naturally increase testosterone levels while staying within the normal healthy range

The most popular way is to combine with a good tasting protein powder. Advanced BCAA’s taste very bitter due to the high amount of peptides. Peptides taste very bitter. You want to use 1 tsp of Advanced BCAA’s with every serving of protein powder. This will really upgrade the quality of the protein powder by adding BCAA, AND in peptides form. If you are using a whey protein you’ll increase the overall BCAA content by over 20%
Both Beast Sports’ Super Test and iSatori’s ISA-Test contain a proprietary blend, which means they don’t disclose the amount of each and every ingredient in the mix. This is only a problem if there is an ingredient tucked into a proprietary blend for which we need to know an amount, like magnesium and zinc. While none of the ingredients in Beast Sports’s proprietary blend raised any red flags, iSatori’s blend contains melatonin, a hormone that helps regulate sleep. Melatonin is an ingredient that has a hard upper limit — Healthline suggests at most 10mg for an adult — and even lower doses can interact poorly with many medications. Since we can’t confirm whether the amount of melatonin in iSatori’s proprietary blend is under 10mg, we cut iSatori.
For this reason I recommend doing your own research on this supplement before taking it. 5g of ground up dried powder is what was used in the studies. I recommend taking 1-2 capsules of the concentrated form from Paradise Herbs. Alternatively, the Aggressive Strength Test Booster also has MP in its formula so you may prefer to use that blend instead. 
It could be said that testosterone is what makes men, men. It gives them their characteristic deep voices, large muscles, and facial and body hair, distinguishing them from women. It stimulates the growth of the genitals at puberty, plays a role in sperm production, fuels libido, and contributes to normal erections. It also fosters the production of red blood cells, boosts mood, and aids cognition.
In addition to weightlifting, studies have shown that HIIT workouts can also help boost testosterone levels. For those of you who don’t know, HIIT stands for high-intensity interval training. It calls for short, intense bursts of exercise, followed by a less-intense recovery period. You repeat with the intense/less-intense cycle several times throughout the workout. In addition to increasing T, HIIT has been shown to improve athletic conditioning and fat metabolism, as well as increase muscle strength.
A large number of trials have demonstrated a positive effect of testosterone treatment on bone mineral density (Katznelson et al 1996; Behre et al 1997; Leifke et al 1998; Snyder et al 2000; Zacharin et al 2003; Wang, Cunningham et al 2004; Aminorroaya et al 2005; Benito et al 2005) and bone architecture (Benito et al 2005). These effects are often more impressive in longer trials, which have shown that adequate replacement will lead to near normal bone density but that the full effects may take two years or more (Snyder et al 2000; Wang, Cunningham et al 2004; Aminorroaya et al 2005). Three randomized placebo-controlled trials of testosterone treatment in aging males have been conducted (Snyder et al 1999; Kenny et al 2001; Amory et al 2004). One of these studies concerned men with a mean age of 71 years with two serum testosterone levels less than 12.1nmol/l. After 36 months of intramuscular testosterone treatment or placebo, there were significant increases in vertebral and hip bone mineral density. In this study, there was also a significant decrease in the bone resorption marker urinary deoxypyridinoline with testosterone treatment (Amory et al 2004). The second study contained men with low bioavailable testosterone levels and an average age of 76 years. Testosterone treatment in the form of transdermal patches was given for 1 year. During this trial there was a significant preservation of hip bone mineral density with testosterone treatment but testosterone had no effect on bone mineral density at other sites including the vertebrae. There were no significant alterations in bone turnover markers during testosterone treatment (Kenny et al 2001). The remaining study contained men of average age 73 years. Men were eligible for the study if their serum total testosterone levels were less than 16.5 nmol/L, meaning that the study contained men who would usually be considered eugonadal. The beneficial effects of testosterone on bone density were confined to the men who had lower serum testosterone levels at baseline and were seen only in the vertebrae. There were no significant changes in bone turnover markers. Testosterone in the trial was given via scrotal patches for a 36 month duration (Snyder et al 1999). A recent meta-analysis of the effects on bone density of testosterone treatment in men included data from these studies and two other randomized controlled trials. The findings were that testosterone produces a significant increase of 2.7% in the bone mineral density at the lumber spine but no overall change at the hip (Isidori et al 2005). These results from randomized controlled trials in aging men show much smaller benefits of testosterone treatment on bone density than have been seen in other trials. This could be due to the trials including patients who are not hypogonadal and being too short to allow for the maximal effects of testosterone. The meta-analysis also assessed the data concerning changes of bone formation and resorption markers during testosterone treatment. There was a significant decrease in bone resorption markers but no change in markers of bone formation suggesting that reduction of bone resorption may be the primary mode of action of testosterone in improving bone density (Isidori et al 2005).
Testosterone is a key hormone as it relates to both sexual drive and muscle growth. Testosterone boosters are meant to increase testosterone levels in the blood. Now while most healthy men under the age of 65 may not need a testosterone boosting supplement, it is true that testosterone levels decrease as we get older. That could lead to a host of things from a loss in muscle mass to problems performing in the bedroom. There are natural testosterone booster, however, and you should consider those to minimize potential side effects.
There are two ways that we determine whether somebody has low testosterone. One is a blood test and the other is by characteristic symptoms and signs, and the correlation between those two methods is far from perfect. Generally men with the lowest testosterone have the most symptoms and men with highest testosterone have the least. But there are some men who have low levels of testosterone in their blood and have no symptoms.

The overweight men participated in one German study. The first group of the participants used a placebo for one year. The second group of the participants consumed vitamin D3. All the participants aspired to shed excessive weight. Those men who took this vitamin lost up to 6 kg of unwanted weight. Also, they got the additional bonus; that is, the increase in testosterone production by about 25%.4
Of course, testosterone’s primary function is to bring about secondary sexual characteristics in men. A healthy dose of testosterone is shown to treat conditions such as impotence. Men with fertility issues benefit from increased levels of testosterone in the body. The aging process slows down the rate of testosterone production by the adrenals and testes. It is irreversible and one of the only means to mediate the effects of low testosterone concentration is to include testosterone boosting agents in your regimen.
After various studies in animals had shown anabolic (muscle building) properties among the various Fenugreek benefits, a study was conducted on men undergoing resistance training. During the study the participants trained in a supervised manner 4 times a week for 8 weeks. Although the levels of DHT (Dihydrotestosterone) were reduced in those taking the Fenugreek supplement, other hormonal markers were not affected[4]. Another study further supported those findings, while also reporting that those taking the supplement witnessed an additional 2kg of fat loss and 2kg more muscle mass gain over the same period[5]. Impressive results indeed.
So, this past summer I talked with my doctor about starting T injections to see if that would work. I started injection 1 small bottle every 2 weeks. I started some time in later July, 2016. After around the 3 injection I had a blood test and my T level was OVER 800, something like 832. Apparently, my body reacted and took to it very quickly and easily, but the T level was now TOO high. So, I extended the injection interval to 18 days instead of 15 days. I just had another blood test last week and my T level was in the mid 600’s. It’s better now, but my doctor and I want to get that down to around 500, so I’m going to 20-21 days and see what happens.
As with cognitive effects, previous studies examining CVD changes following testosterone treatment have been conflicting and inconclusive. Dr. Budoff and his research team used coronary computed tomographic angiography (CCTA) to assess 138 men, including 73 treated with testosterone and 65 receiving placebo, for changes in coronary artery plaque volume after 1 year.
There is a dirty little secret about testosterone cream that almost no one knows, and I’m going to share it here. Please don’t abuse it. If you take a vanishingly small dose of testosterone cream and apply it to your labia and the vulva (or your partner’s), you will witness a form of vasodilation rarely seen no matter how good you are in bed. It has a profound local effect and will produce a night you won’t forget for years.
I have tried pellets, I went from 5 grams/day gel, to 10 grams, had little change due to work schedule and no energy made it difficult to manage daily. Levels got down to 78 at one point. Testo pellets worked great but it took 10 to make a difference and it brought me up to the 300-400 range. My body rejected 3 pellets and expelled them. Tried axiron, didn’t work, natesto, which the doc never heard off next, a Nasal spray which helped but the bottle ran out 5 days early either by my mistake or dosage problems. Back to 10 grams Testim AG ($360 after deductible) which helps if i could stay consistent but I’m 28. With a job, and health insurance, deductible issues I can not afford 800 dollars a month, 360 after deductible. Recent levels of FSH/LH are .7 and 1.2 (low). Total testosterone 114, free 18.9, and bioavalability at 39.6 (low). I had a MRI of my pituitary gland today, and get results next week. Hoping to start depo T next week as I return to work. If I can recommend anything to anyone, is make sure it’s affordable, you have the time or energy to apply/administer, and understand most people will not understand what you are going through. 2 killers of testosterone are chronic stress and lack of sleep. In 3 years of treatment I wish I came to this man’s article and others and read up prior because I’m on the brink of losing everything I’ve worked for due to hypogonadism. Wish you all results and good health, and thank you for a great article!
Over time, the testicular “machinery” that makes testosterone gradually becomes less effective, and testosterone levels start to fall, by about 1% a year, beginning in the 40s. As men get into their 50s, 60s, and beyond, they may start to have signs and symptoms of low testosterone such as lower sex drive and sense of vitality, erectile dysfunction, decreased energy, reduced muscle mass and bone density, and anemia. Taken together, these signs and symptoms are often called hypogonadism (“hypo” meaning low functioning and “gonadism” referring to the testicles). Researchers estimate that the condition affects anywhere from two to six million men in the United States. Yet it is an underdiagnosed problem, with only about 5% of those affected receiving treatment.
Testosterone booster products obtained from trusted sources and administered as per the recommendations of the manufacturer may still present some health risks. The present case provided weak evidence of causality between acute liver injury and a commercial testosterone booster. To guarantee an optimal outcome with no severe side effects, further research is warranted to confirm the present findings and determine whether the effects observed in this case report would be statistically significant in larger samples.
Testosterone is the primary male sex hormone and an anabolic steroid. In male humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair.[2] In addition, testosterone is involved in health and well-being,[3] and the prevention of osteoporosis.[4] Insufficient levels of testosterone in men may lead to abnormalities including frailty and bone loss.

On review of the patient’s history, he was found to have undergone laboratory tests before starting to use the aforementioned testosterone booster product. All blood parameters (testosterone hormone and full chemical profile) before product intake were in the normal range. A physical examination that included blood pressure and pulse assessments showed nothing out of the ordinary, and the man appeared to be in good condition before product consumption. After that medical checkup, the athlete began to consume the product for 42 continuous days divided into 2 cycles (each cycle comprised 24 days). The daily dose was a single pack of Universal Nutrition Animal Stak (ingredients are listed in Table 1), following the exact direction of the manufacturing company hoping to get the best results.
It also has vitamin B6. One study called out folate and vitamins B6 and B12 as important nutrients for athletes to achieve optimal health and performance. Vitamin B6 is commonly found in food, like fortified cereals, and as with magnesium, it’s possible to have too much vitamin B6. The NIH recommends an upper daily limit for adults of 100mg per day. Beast Sports comes well under this limit at 10mg per day, but still well above the minimum recommended dose of 1.7mg needed to see benefits.
I am generally dubious about supplement claims & have tried a few other Testosterone boosters which had no effect I could tell. Being desperate to find something to help me feel better, I ordered Dr Martin's T Booster. It arrived on May 14th and after the first day I felt better & noticeably had more energy. I don't have that tired dead feeling every morning now when trying to get out of bed. I am able to do some work & physical activities without being exhausted to the point of being sick. I have been taking Dr Martin's T-Booster for 8 days now. While I am not out running marathons yet, I am feeling much better & hope to continue getting better as I keep taking it
Although it’s rare to see swelling caused by fluid retention, physicians need to be careful when prescribing testosterone to men with compromised kidney or liver function, or some degree of congestive heart failure. It can also increase the oiliness of the skin, so that some men get acne or pimples, but that’s quite uncommon, as are sleep apnea and gynecomastia (breast enlargement).
The unsexy truth is that increasing T naturally simply comes down to making some long-term changes in your diet and lifestyle. As you’ll see, what I did to increase T largely boils down to eating better, exercising smarter, and getting more sleep. That’s pretty much it. But as with most things in life, the devil is in the details, so I’ll share with you exactly what I did and provide research that explains why the things I did helped boost my testosterone.
Testosterone is indisputably the king of hormones when it comes to the gym. While it’s responsible for reproductive development, it’s better known for its major role in promoting muscle growth, increasing bone density, and even how body fat is distributed. Testosterone levels are also a huge influencer in terms of overall health and emotional state. With age, however, natural testosterone production naturally declines, leading to higher levels of body fat and more difficulty building muscle, not to mention a decrease in libido.
61y/o with 18month progressive lethargy, depressed mood, no sex drive, no erections. Doc put me on cymbalta (slept even more than 14hrs daily) then on Wellbutrin. All the time I was pushing for T testing. Came back low in March of this year and put on IM cypionate 100mg q3 weeks. Even I knew that was too low and infrequent. Nonetheless, that how it’s been since April. Finally got urology consult in Shreveport and got a level done at that time. Was 127 just two weeks after last injection. He is going to bump me up to 300mg q2 weeks and do a level 2 days after first injection and 1 day before next shot. Since I’m getting care thru VA, it’s a waiting game. Saw urologist last week. Prob won’t see testostosterone in mail for another week or two. I’m excited to feel like living again, not sleeping all the time, and perhaps some nooky now and then . Appreciated this article arm subsequent posts and personal trials. Would love to find a competent and assertive urologist in my area of Louisiana. I’m around Monroe….so if you know one, let me know!
^ Butenandt A, Hanisch G (1935). "Uber die Umwandlung des Dehydroandrosterons in Androstenol-(17)-one-(3) (Testosterone); um Weg zur Darstellung des Testosterons auf Cholesterin (Vorlauf Mitteilung). [The conversion of dehydroandrosterone into androstenol-(17)-one-3 (testosterone); a method for the production of testosterone from cholesterol (preliminary communication)]". Chemische Berichte (in German). 68 (9): 1859–62. doi:10.1002/cber.19350680937.
From there, you’ll want to adjust how you train, since certain activities provide an especially powerful stimulus for testosterone. Research published in the journal Sports Medicine found that in order to experience a strong testosterone response from exercise, your workouts should be high in volume and produce a metabolic response. Churn through many exercises, sets, and reps, and focus on intense bursts of exercise with short rest periods.

For this reason, after the 2008 financial market meltdown, some commentators put the blame for the crash on the male-dominated profession, arguing that men take too many risks, and the economy would do better and be more stable if it was run by women. Of course, risk-taking does come with inherent risk, but it has also been responsible for the lion’s share of society’s progress and innovation since the dawn of time. Financial markets would likely not exist – period – without testosterone-driven risk-taking.
In accordance with sperm competition theory, testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats.[40] This reaction engages penile reflexes (such as erection and ejaculation) that aid in sperm competition when more than one male is present in mating encounters, allowing for more production of successful sperm and a higher chance of reproduction.

A recent study conducted on trained subjects showed that squats stimulated a greater testosterone response than leg presses.10 Stick with multijoint exercises like squats, bench presses, and deadlifts—the kinds of compound lifts that'll help jack up your testosterone levels. Since machines isolate a muscle you're working (less stabilizer activity), they're not as good a choice compared to free weights.
Another study in 2015 by Melville and friends gave subjects either three or six grams of DAA per day for a 14 days (2 weeks). Researchers noted that the 3g dose of D-aspartic acid did not result in any meaningful changes in testosterone levels (or any other anabolic hormones for that matter).[3] However, the group of men receiving 6g per day experienced a significant reduction in both total testosterone and free testosterone levels, with no concurrent change in other hormones tested.[3]
Ok. So this product is meant to be taken continuously and without side-effects. But my question is, will there be replenishment from this product in aiding the body's natural ability to produce testosterone? In other words, will there ever be a time when I can say well I don't have to take this any more as my body is producing testosterone again on it's own and my muscle mass has been enhanced?
One study showed that six months of zinc supplementation among slightly zinc-deficient elderly men doubled serum levels of testosterone. And another eight-week trial found that college football players who took a nightly zinc supplement showed increased T-levels and increased leg strength that was 250 percent greater than a placebo! Holy quads, Batman! Research has also shown deficiencies in zinc to be a risk factor for infertility caused by low testosterone levels.

The reason I started the experiment at that point is because I know a lot of guys who live my last-August lifestyle all the time, and I wanted to see what would happen to an “average” guy who turned things around. At the same time, there was no “normal” time in my life which would have been better for me to start the experiment. My stress level and diet fluctuates throughout the year anyway, so at any point, factors in my current lifestyle would have influenced the results. I wanted to begin at “ground zero.”
The other problem researchers run into when studying the benefits of testosterone is distinguishing between “cause” and “effect.” Is it T that’s providing all these great health benefits or does simply being healthy give you optimal levels of testosterone? It’s tricky because in some instances the answer is “both.” Testosterone (like all hormones) often plays a part in a “virtuous cycle” that regulates a whole host of  processes in our bodies — as you increase T, you get healthier; as you get healthier, your T levels rise. It can also play a part in a “vicious cycle” — as your T levels go down, your health suffers; as your health suffers, your T levels decrease even more.
Cross-sectional studies have found a positive association between serum testosterone and some measures of cognitive ability in men (Barrett-Connor, Goodman-Gruen et al 1999; Yaffe et al 2002). Longitudinal studies have found that free testosterone levels correlate positively with future cognitive abilities and reduced rate of cognitive decline (Moffat et al 2002) and that, compared with controls, testosterone levels are reduced in men with Alzheimer’s disease at least 10 years prior to diagnosis (Moffat et al 2004). Studies of the effects of induced androgen deficiency in patients with prostate cancer have shown that profoundly lowering testosterone leads to worsening cognitive functions (Almeida et al 2004; Salminen et al 2004) and increased levels of serum amyloid (Gandy et al 2001; Almeida et al 2004), which is central to the pathogenesis of Alzheimer’s disease (Parihar and Hemnani 2004). Furthermore, testosterone reduces amyloid-induced hippocampal neurotoxity in vitro (Pike 2001) as well as exhibiting other neuroprotective effects (Pouliot et al 1996). The epidemiological and experimental data propose a potential role of testosterone in protecting cognitive function and preventing Alzheimer’s disease.
There are three ways to increase testosterone activity naturally with simple lifestyle choices. The first is to increase total testosterone production. Second is to increase the amount of free and active testosterone that can stimulate testosterone receptors. The third is to unblock testosterone receptors, opening them up for testosterone stimulation.
DHEA (dehydroepiandrosterone) extract - this is a chemical that used in your body which a ‘hormone precursor’. This means it’s the chemical used by the body to create hormones like oestrogen or testosterone. When taken as supplement it is believed to boost testosterone levels, but DHEA has not been shown to increase testosterone in men. DHEA comes in two form:
Japanese Knotweed (a.k.a Hu Zhang or Polygonum cuspidatum) is highlighted by WebMD as needing more evidence to rate its effectiveness in a number of different areas: like treating constipation and liver or heart disease. They also warn that it can interact poorly with medications that are changed and broken down by the liver, and those that slow blood clotting (anticoagulants and antiplatelets).
Natural testosterone boosters also help to increase the amount of free testosterone in the body. There are a couple of different ingredients they use that help with this. One of these ingredients is stinging nettle. Stinging nettle is actually able to bind to the globulin in place of testosterone, therefore leaving more free testosterone in the body that is unbound.
A: Endocrinology is a very difficult subject, some physicians and pharmacists alike have more difficulty with endocrinology than neurology. The reason for this is that there is no clear cut answer. Every hormone interacts with another hormone system in the body whether it be parathyroid hormone, cortisol, follicle stimulating hormone, etc. By in large, testosterone will increases lean body mass, which is to say that it typically increases muscle and or bone mass. We use it in the hospital to put weight on in patients needing to gain weight. That is partially the reason why we refer to testosterone as an "anabolic" hormone; anabolic meaning 'to build'. For more information, please visit us here at: //www.everydayhealth.com/drugs/testosterone Matt Curley, PharmD
Carbs play a big part in determining your Testosterone levels. Let's start with what to avoid. First, research shows that a large serving of sugar (75g of glucose), decreased Testosterone levels by as much as 25%! (25 & 26). I know this is a pretty extreme dosage, but you may want to avoid massive servings of sugar! Also, men who have Metabolic syndrome have lower Testosterone levels (27). Metabolic syndrome is often brought about by chronic high blood sugar which leads to insulin resistance.

during therapy. It is very hard to find a local endo who is thinking with his head vs complying with old trt programs. I tool clomid in the past to see what it would do and it elevated my t level to 520 in 2 weeks from low 220. Aromason will do same but clomid is more potent. Not sure what the long effect would be since you tend to get bit moody on clomid after 2 months. LH is also being affected in negative way since the lh receptors can burn out to a degree. I will contact the trt clinic in order to start my trt as they have much more experience with these things.


The content here is for information purposes only. By delivering the information contained herein is does not mean preventing, diagnosing, mitigating, treating or curing any type of medical condition or disease. When beginning any natural supplementation regiment or integrative treatment, the advice of professionally licensed healthcare providers is advisable to seek.


Statins are some of the most prescribed drugs in the world for reducing cholesterol levels and preventing heart disease. Various studies in the 1990s, including a study published in the ‘European Journal of Clinical Nutrition,’ supported the claim that Fenugreek could help reduce cholesterol levels[2]. One possible explanation is the high fiber content in fenugreek.  A fiber-rich diet has been shown to help reduce the levels of LDL (‘bad’ cholesterol) in your blood. (Note: The validity of the various studies from the 1990s have been questioned though because of small sample sizes[3])


Testosterone belongs to a class of male hormones called androgens, which are sometimes called steroids or anabolic steroids. In men, testosterone is produced mainly in the testes, with a small amount made in the adrenal glands. The brain's hypothalamus and pituitary gland control testosterone production. The hypothalamus instructs the pituitary gland on how much testosterone to produce, and the pituitary gland passes the message on to the testes. These communications happen through chemicals and hormones in the bloodstream.
Two of the immediate metabolites of testosterone, 5α-DHT and estradiol, are biologically important and can be formed both in the liver and in extrahepatic tissues.[155] Approximately 5 to 7% of testosterone is converted by 5α-reductase into 5α-DHT, with circulating levels of 5α-DHT about 10% of those of testosterone, and approximately 0.3% of testosterone is converted into estradiol by aromatase.[2][155][161][162] 5α-Reductase is highly expressed in the male reproductive organs (including the prostate gland, seminal vesicles, and epididymides),[163] skin, hair follicles, and brain[164] and aromatase is highly expressed in adipose tissue, bone, and the brain.[165][166] As much as 90% of testosterone is converted into 5α-DHT in so-called androgenic tissues with high 5α-reductase expression,[156] and due to the several-fold greater potency of 5α-DHT as an AR agonist relative to testosterone,[167] it has been estimated that the effects of testosterone are potentiated 2- to 3-fold in such tissues.[168]
In order to discuss the biochemical diagnosis of hypogonadism it is necessary to outline the usual carriage of testosterone in the blood. Total serum testosterone consists of free testosterone (2%–3%), testosterone bound to sex hormone binding globulin (SHBG) (45%) and testosterone bound to other proteins (mainly albumin −50%) (Dunn et al 1981). Testosterone binds only loosely to albumin and so this testosterone as well as free testosterone is available to tissues and is termed bioavailable testosterone. Testosterone bound to SHBG is tightly bound and is biologically inactive. Bioavailable and free testosterone are known to correlate better than total testosterone with clinical sequelae of androgenization such as bone mineral density and muscle strength (Khosla et al 1998; Roy et al 2002). There is diurnal variation in serum testosterone levels with peak levels seen in the morning following sleep, which can be maintained into the seventh decade (Diver et al 2003). Samples should always be taken in the morning before 11 am to allow for standardization.
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