Testosterone is the main hormone associated with muscle mass, strength gains, and libido. But that's far from the only thing it does in the body. As Chris Lockwood, Ph.D., explains in the article "All About Testosterone," it impacts everything from mood and memory to bone health—but yes, to be clear, it also makes muscles bigger and stronger, and helps increase endurance and athletic performance.
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Testosterone has two major effects on bones: (a) through conversion to estradiol by way of the enzyme, aromatase, testosterone inhibits osteoclastic activity and hence bone resorption; and (b) through conversion to DHT via 5-α-reductase, it stimulates osteoblastic activity and so enhances the laying down of bone (Tivesten et al 2004; Davey and Morris 2005). Hypogonadal men are at risk for the development of osteopenia or osteoporosis and hence for subsequent fracture (Fink et al 2006). About one-third of all osteoporotic hip fractures occur in men and the risk of any osteoporotic fracture in men over 50 is as high as 25 percent (Seeman 1997; Adler 2006). Although treatment with testosterone in hypogonadal men increases bone mineral density (Katznelson et al 1996), it has not yet been established that this results in a reduction in fracture rate.
During the second trimester, androgen level is associated with sex formation.[13] This period affects the femininization or masculinization of the fetus and can be a better predictor of feminine or masculine behaviours such as sex typed behaviour than an adult's own levels. A mother's testosterone level during pregnancy is correlated with her daughter's sex-typical behavior as an adult, and the correlation is even stronger than with the daughter's own adult testosterone level.[14]
Few examples: In this 2014 study, a bunch of researchers tested multiple different diets with added Lactobacillus Reuteri on male rodents. In every single case, the addition of L.Reuterii to the feed increased testosterone levels, increased luteinizing hormone levels, increased testicular size & weight, prevented age-related testicular shrinkage, improved semen parameters, and even increased markers of social domination.

Sexual arousal - boosting testosterone can improve sexual arousal, even if you have normal testosterone levels. Higher levels of testosterone can make it easier for you to get aroused and can boost your sex drive generally. While this doesn’t affect the physical action of your erections, if you are not getting hard because you’re not aroused then boosting testosterone could help.
It may also become a treatment for anemia, bone density and strength problems. In a 2017 study published in the journal of the American Medical Association (JAMA), testosterone treatments corrected anemia in older men with low testosterone levels better than a placebo. Another 2017 study published in JAMA found that older men with low testosterone had increased bone strength and density after treatment when compared with a placebo. 
A number of research groups have tried to further define the relationship of testosterone and body composition by artificial alteration of testosterone levels in eugonadal populations. Induction of a hypogonadal state in healthy men (Mauras et al 1998) or men with prostate cancer (Smith et al 2001) using a gonadotrophin-releasing-hormone (GnRH) analogue was shown to produce increases in fat mass and decreased fat free mass. Another experimental approach in healthy men featured suppression of endogenous testosterone production with a GnRH analogue, followed by treatment with different doses of weekly intramuscular testosterone esters for 20 weeks. Initially the experiments involved men aged 18–35 years (Bhasin et al 2001) but subsequently the study was repeated with a similar protocol in men aged 60–75 years (Bhasin et al 2005). The different doses given were shown to produce a range of serum concentrations from subphysiological to supraphysiological (Bhasin et al 2001). A given testosterone dose produced higher serum concentrations of testosterone in the older age group (Bhasin et al 2005). Subphysiological dosing of testosterone produced a gain in fat mass and loss of fat free mass during the study. There were sequential decreases in fat mass and increases in fat free mass with each increase of testosterone dose. These changes in body composition were seen in physiological and supraphysiological treatment doses. The trend was similar in younger versus older men but the gain of fat mass at the lowest testosterone dose was less prominent in older patients (Bhasin et al 2001; Bhasin et al 2005). With regard to muscle function, the investigators showed dose dependent increases in leg strength and power with testosterone treatment in young and older men but there was no improvement in fatigability (Storer et al 2003; Bhasin et al 2005).

Both men and women with Alzheimer’s Disease were found to have an increased concentration of SHBG and decreased free androgen index when compared with controls (Paoletti et al 2004). In a prospective study of 574 men whose baseline age span was 32–87 years and who were followed for a mean of 19.1 years (range, 4–37), the risk of developing Alzheimers’ Disease decreased 26 percent for each 10 unit increase in free testosterone index. The authors concluded that testosterone may be important for the prevention and treatment of AD (Moffat et al 2004).

Testosterone is observed in most vertebrates. Testosterone and the classical nuclear androgen receptor first appeared in gnathostomes (jawed vertebrates).[189] Agnathans (jawless vertebrates) such as lampreys do not produce testosterone but instead use androstenedione as a male sex hormone.[190] Fish make a slightly different form called 11-ketotestosterone.[191] Its counterpart in insects is ecdysone.[192] The presence of these ubiquitous steroids in a wide range of animals suggest that sex hormones have an ancient evolutionary history.[193]
6., 7. JK, Udani, George AA, Musthapa M, Pakdaman MN, and Abas A. "Effects of a Proprietary Freeze-Dried Water Extract of Eurycoma Longifolia (Physta) and Polygonum minus on Sexual Performance and Well-Being in Men: A Randomized, Double-Blind, Placebo-Controlled Study." National Center for Biotechnology Information. U.S. National Library of Medicine, 12 Jan. 2014.
Vitamin D3. Vitamin D3 actually isn’t a vitamin, it’s a hormone — a really important hormone that provides a whole host of health benefits. Our bodies can naturally make vitamin D from the sun, but recent studies have shown that many Westerners are vitamin D3 deprived because we’re spending less and less time outdoors. When we do decide to venture outside, we slather our bodies with sunscreen, which prevents the sun reaching our skin to kick-off vitamin D3 production. If you’re not getting enough sun, you may have a vitamin D3 deficiency, which may contribute to low T levels. If you think you need more vitamin D3, supplement it with a pill. Studies have shown that men who take this supplement see a boost in their testosterone levels. Because I have a darker complexion — which makes me prone to Vitamin D3 deficiency — I took 4,000 IU of vitamin D3 in the morning.
This being my initial use of product I do find an overall improvement in mind and body "maleness" related to focused goal and strength improvements. Has it turned me into a super stud..no, but at a recent 60th birthday, increased desire has added to performance and that is what I was looking for.I have reinstated diet and exercise that also has made physical and mental health achievements Will finish current bottle, and evaluate overall products worth once completed. Further evaluation pending...
Testogenix is quickly becoming one of the best-selling testosterone supplements on the market! Its 12 clinically-proven ingredients have helped men everywhere dramatically raise their testosterone levels and do it safely with a 100% All-Natural Ingredients. Priced under $40, it is no wonder why Testogenix has become our User’s Favorite Testosterone Supplement. When surveyed, Testogenix was chosen as their top choice for its affordable, safe & effective formulation all for UNDER $40!
Among the changes which occur with aging are those that affect several aspects of the endocrine system which reduces its secretions to varying degrees in different individuals. These reductions in secretions are identified by a poor but widely recognized appellation, the “pauses”: menopause (decreased ovarian function), adrenopause (decreased adrenal function, especially with regard to dehydroepiandrosterone secretion), somatopause (decreased growth hormone production), andropause (decreased hypothalamic-pituitary testicular function with diminished testosterone availability and impaired spermatogenesis) (Lamberts 1997).

However, testosterone is only one of many factors that aid in adequate erections. Research is inconclusive regarding the role of testosterone replacement in the treatment of erectile dysfunction. In a review of studies that looked at the benefit of testosterone in men with erection difficulties, showed no improvement with testosterone treatment. Many times, other health problems play a role in erectile difficulties. These can include:
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Testosterone is only one of many factors that influence aggression and the effects of previous experience and environmental stimuli have been found to correlate more strongly. A few studies indicate that the testosterone derivative estradiol (one form of estrogen) might play an important role in male aggression.[66][67][68][69] Studies have also found that testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus.[70]
“This study establishes testosterone levels at which various physiological functions start to become impaired, which may help provide a rationale for determining which men should be treated with testosterone supplements,” Finkelstein says. “But the biggest surprise was that some of the symptoms routinely attributed to testosterone deficiency are actually partially or almost exclusively caused by the decline in estrogens that is an inseparable result of lower testosterone levels.”

It sounds like a creature from Jurassic World, but this plant is worth learning to pronounce, especially if you haven’t had great sex since dinosaurs roamed the earth. A 2012 study showed that consuming six grams of tribulus root for 60 days improved erections and frequency of sex in men with low sperm counts. It also reduced sexual fatigue. Furthermore, their testosterone jumped by a whopping 16%. “Trib,” as it’s called, is thorny and bitter, so look to a supplement for consuming it. Epiq’s Quad Test includes Tribulus terrestris. (epiqresults.com)

Puberty occurs when there is an “awakening” of the hypothalamic-pituitary axis. The hypothalamus increases its secretion of gonadotropin releasing hormone (GnRH) which in turn stimulates the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH). This leads to a significant increase in the production of testicular testosterone and the induction of the well-known secondary sex characteristics associated with puberty: growth spurt, increased libido, increased erectile function, acne, increased body hair, increased muscle mass, deepening of the voice, spermatogenesis, gynecomastia (usually transient).
Estrogen is important in men, but too high of a level has all sorts of negative consequences – ranging from heart attacks to prostate cancer (32 & 33). The balance between testosterone and estrogen (or estradiol) is critical for a man. If the ratio is out and estrogen starts to dominate you run into all sorts of issues – such as breast cell growth, prostate enlargement and of course lower testosterone.

Because of the mass production, conventional pigs are fed with GMO soy and corn, and they’re living in such horrid conditions that they’re pumped full of antibiotics to ensure that the pigs won’t get any inflammatory diseases, and then they’re fed & injected with ridiculous amounts of estrogen and growth hormone to make the pigs fatter and bigger in record times.

Consume vegetable carbohydrates and healthy fats. Your body requires the carbohydrates from fresh vegetables rather than grains and sugars. In addition to mono- or polyunsaturated fats found in avocados and raw nuts, saturated fats are also essential to building your testosterone production. According to research, there was a decrease in testosterone stores in people who consumed a diet low in animal-based fat.11 Aside from avocados and raw nuts, ideal sources of healthy fat that can boost your testosterone levels include:

It is important not to use any DHEA product without the supervision of a professional. Find a qualified health care provider who will monitor your hormone levels and determine if you require supplementation. Rather than using an oral hormone supplementation, I recommend trans-mucosal (vagina or rectum) application. Skin application may not be wise, as it makes it difficult to measure the dosage you receive. This may cause you to end up receiving more than what your body requires.
It's important to understand that your body requires saturated fats from animal and vegetable sources (such as meat, dairy, certain oils, and tropical plants like coconut) for optimal functioning, and if you neglect this important food group in favor of sugar, grains and other starchy carbs, your health and weight are almost guaranteed to suffer. Examples of healthy fats you can eat more of to give your testosterone levels a boost include:
Testosterone supplements are typically used by men who want to increase the level of the male hormone testosterone that controls functions such as sexual desire and muscle gain. There are several types of over-the-counter testosterone supplements available in nutritional supply stores. You should speak to your doctor before using any type of testosterone supplement since none of the effects advertised have been approved by the Food and Drug Administration. Additionally, there are prescription-based testosterone therapies that produce better results.
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:

Yeah a lot of information has come out in the last decade or so proving that cholesterol is in fact good for you, and actually has no correlation to heart disease. But I think it will be a few more years until the world will shift such a strong belief that cholesterol is the enemy. If you are interested in this you should read grain brain. It talks all about (and proves) how high carbohydrates are actually the reason for “high cholesterol” and a high fat low carb diet is great for your body, and more importantly your brain.
If your levels are indeed low, there are a number of synthetic and bioidentical testosterone products on the market, as well as DHEA, which is the most abundant androgen precursor prohormone in the human body, meaning that it is the largest raw material your body uses to produce other vital hormones, including testosterone in men and estrogen in women.
That there is an association between depression and testosterone concentration seems possible because of the observation that depression may be associated with reduced testosterone concentrations, hypogonadal men may have their symptoms of depression relieved by TRT and that testosterone itself may have anti-depressant properties (Pope et al 2003). The evidence, however, is inconsistent. Seidman and colleagues (2002), for example, found that there was no relationship between testosterone and depression but there was an association of testosterone with dysthymia. McIntyre and colleagues (2006), on the other hand, found that middle-aged men with depression did have a reduction in bio-available testosterone.

If a young man's low testosterone is a problem for a couple trying to get pregnant, gonadotropin injections may be an option in some cases. These are hormones that signal the body to produce more testosterone. This may increase the sperm count. Hedges also describes implantable testosterone pellets, a relatively new form of treatment in which several pellets are placed under the skin of the buttocks, where they release testosterone over the course of about three to four months. Injections and nasal gels may be other options for some men.