The participants were seen every 4 weeks. Blood was taken to measure hormone levels, and questionnaires were given to assess physical function, health status, vitality, and sexual function. Body fat and muscle measurements were also taken at the beginning and end of the 16 weeks. The study was funded in part by NIH’s National Institute on Aging (NIA) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Results appeared in the September 12, 2013, issue of the New England Journal of Medicine.

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.
Dr. Anthony’s Notes: Correcting a common zinc deficiency can really help testosterone levels. This is why many supplement companies make testosterone boosting supplement stacks called “ZMA” (which stands for Zinc-Magnesium Aspartate) – which is essentially a combination of zinc and magnesium. Do note that LONG TERM high dose zinc supplementation is NOT a good idea (above 30-40mg). Taking too much zinc can lead to a copper deficiency (the two minerals compete for absorption), which causes problems of its own. Verdict: this is one of the natural testosterone supplements that work. Best Food Sources: Beef, lamb, oysters, pumpkin seeds, cashews, quinoa, turkey, chickpeas How To Take Zinc: 30mg once per day with food is ideal. And as we alluded to above in my “notes,” it's often best to take zinc WITH the next supplement on our list…
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. 
Both testosterone and 5α-DHT are metabolized mainly in the liver.[1][151] Approximately 50% of testosterone is metabolized via conjugation into testosterone glucuronide and to a lesser extent testosterone sulfate by glucuronosyltransferases and sulfotransferases, respectively.[1] An additional 40% of testosterone is metabolized in equal proportions into the 17-ketosteroids androsterone and etiocholanolone via the combined actions of 5α- and 5β-reductases, 3α-hydroxysteroid dehydrogenase, and 17β-HSD, in that order.[1][151][152] Androsterone and etiocholanolone are then glucuronidated and to a lesser extent sulfated similarly to testosterone.[1][151] The conjugates of testosterone and its hepatic metabolites are released from the liver into circulation and excreted in the urine and bile.[1][151][152] Only a small fraction (2%) of testosterone is excreted unchanged in the urine.[151]
Important future developments will include selective androgen receptor modulators (SARMs). These drugs will be able to produce isolated effects of testosterone at androgen receptors. They are likely to become useful clinical drugs, but their initial worth may lie in facilitating research into the relative importance of testosterone’s action at the androgen receptor compared to at other sites or after conversion to other hormones. Testosterone will remain the treatment of choice for late onset hypogonadism for some time to come.
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:

Testosterone is a steroid hormone from the androgen group. Testosterone is primarily secreted from the testes of males. In females, it is produced in the ovaries, adrenal glands and by conversion of adrostenedione in the periphery. It is the principal male sex hormone and an anabolic steroid. In both males and females, it plays key roles in health and well-being. Examples include enhanced libido, energy, immune function, and protection against osteoporosis. On average, the adult male body produces about twenty times the amount of testosterone than an adult female's body does.
^ 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.
Saw palmetto: Uses, dosage, and side effects Saw palmetto is an extract from the berries of a type of palm tree. The berries have traditionally been used to ease urinary and reproductive problems. The extract is now used in herbal remedies to stabilize testosterone. Learn about its use, its effectiveness, the science behind the claims, and any side effects. Read now