Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Testosterone levels generally peak during adolescence and early adulthood. As you get older, your testosterone level gradually declines — typically about 1 percent a year after age 30 or 40. It is important to determine in older men if a low testosterone level is simply due to the decline of normal aging or if it is due to a disease (hypogonadism).

Erectile dysfunction in older men. Because erections primarily involve the blood vessels, it is not surprising that the most common causes in older men are conditions that block blood flow to the penis, such as atherosclerosis or diabetes. Another vascular cause may be a faulty vein, which lets blood drain too quickly from the penis. Other physical disorders, as well as hormonal imbalances and certain operations, may also result in erectile dysfunction.
The rise in testosterone levels during competition predicted aggression in males but not in females.[86] Subjects who interacted with hand guns and an experimental game showed rise in testosterone and aggression.[87] Natural selection might have evolved males to be more sensitive to competitive and status challenge situations and that the interacting roles of testosterone are the essential ingredient for aggressive behaviour in these situations.[88] Testosterone produces aggression by activating subcortical areas in the brain, which may also be inhibited or suppressed by social norms or familial situations while still manifesting in diverse intensities and ways through thoughts, anger, verbal aggression, competition, dominance and physical violence.[89] Testosterone mediates attraction to cruel and violent cues in men by promoting extended viewing of violent stimuli.[90] Testosterone specific structural brain characteristic can predict aggressive behaviour in individuals.[91]
Cavernosography measurement of the vascular pressure in the corpus cavernosum. Saline is infused under pressure into the corpus cavernosum with a butterfly needle, and the flow rate needed to maintain an erection indicates the degree of venous leakage. The leaking veins responsible may be visualized by infusing a mixture of saline and x-ray contrast medium and performing a cavernosogram.[21] In Digital Subtraction Angiography (DSA), the images are acquired digitally.
"Low T" is anything but inevitable. BMJ's Drug and Therapeutics Bulletin says that around 80 percent of 60-year-old men, and half of those in their eighties, have testosterone levels within the normal range for younger men. It concluded, "The evidence that an age-related reduction in testosterone levels causes specific symptoms is weak." The Food and Drug Administration (FDA) meanwhile has not approved testosterone use to improve strength, athletic performance, physical appearance, or prevent aging. And a 2004 report from the Institute of Medicine ("Testosterone and Aging: Clinical Research Directions") called TRT for age-related testosterone decline a "scientifically unproven method."
Erectile dysfunction is known to be associated with general health status, thus, lifestyle modification improves erectile function and decreases the rate of decline of function with aging. One year after discontinuation of smoking, patients were found to have a 25% improvement in erectile quality.16 In addition, multivariate analysis found obesity is associated with erectile dysfunction with an approximately 50% increase in ED in obese men as compared with normal weight men.17
A testicular action was linked to circulating blood fractions – now understood to be a family of androgenic hormones – in the early work on castration and testicular transplantation in fowl by Arnold Adolph Berthold (1803–1861).[174] Research on the action of testosterone received a brief boost in 1889, when the Harvard professor Charles-Édouard Brown-Séquard (1817–1894), then in Paris, self-injected subcutaneously a "rejuvenating elixir" consisting of an extract of dog and guinea pig testicle. He reported in The Lancet that his vigor and feeling of well-being were markedly restored but the effects were transient,[175] and Brown-Séquard's hopes for the compound were dashed. Suffering the ridicule of his colleagues, he abandoned his work on the mechanisms and effects of androgens in human beings.
Some anti-aging physicians also use sublingual ( taken under the tongue) forms of non-bioidentical testosterone like oxandrolone. I took oxandrolone with a physician’s guidance for about two weeks, and I got pimples and hair loss. I quit and was bummed that it didn’t generate enough impact to write a blog post about it. I have continued to recommend bioidentical testosterone since.
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]
Dr. Ronald Swerdloff, chief of the endocrinology division at the Harbor-UCLA Medical Center and a professor of medicine at UCLA's David Geffen School of Medicine, served on the panel of experts who developed the Endocrine Society's guidelines. He is also the principal investigator for one of the 12 sites of The Testosterone Trial in Older Men, a nationwide study funded mainly by the National Institute on Aging. The study of 800 men over age 65 with low testosterone is looking at whether men using AndroGel for one year, compared to placebo, will show improvements in walking speed, sexual activity, vitality, memory, and anemia. The study will be completed in June 2015.
The Organon group in the Netherlands were the first to isolate the hormone, identified in a May 1935 paper "On Crystalline Male Hormone from Testicles (Testosterone)".[177] They named the hormone testosterone, from the stems of testicle and sterol, and the suffix of ketone. The structure was worked out by Schering's Adolf Butenandt, at the Chemisches Institut of Technical University in Gdańsk.[178][179]
In addition to conjugation and the 17-ketosteroid pathway, testosterone can also be hydroxylated and oxidized in the liver by cytochrome P450 enzymes, including CYP3A4, CYP3A5, CYP2C9, CYP2C19, and CYP2D6.[151] 6β-Hydroxylation and to a lesser extent 16β-hydroxylation are the major transformations.[151] The 6β-hydroxylation of testosterone is catalyzed mainly by CYP3A4 and to a lesser extent CYP3A5 and is responsible for 75 to 80% of cytochrome P450-mediated testosterone metabolism.[151] In addition to 6β- and 16β-hydroxytestosterone, 1β-, 2α/β-, 11β-, and 15β-hydroxytestosterone are also formed as minor metabolites.[151][152] Certain cytochrome P450 enzymes such as CYP2C9 and CYP2C19 can also oxidize testosterone at the C17 position to form androstenedione.[151]
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Another effect that can limit treatment is polycythemia, which occurs due to various stimulatory effects of testosterone on erythropoiesis (Zitzmann and Nieschlag 2004). Polycythemia is known to produce increased rates of cerebral ischemia and there have been reports of stroke during testosterone induced polycythaemia (Krauss et al 1991). It is necessary to monitor hematocrit during testosterone treatment, and hematocrit greater than 50% should prompt either a reduction of dose if testosterone levels are high or high-normal, or cessation of treatment if levels are low-normal. On the other hand, late onset hypogonadism frequently results in anemia which will then normalize during physiological testosterone replacement.
The amount of testosterone synthesized is regulated by the hypothalamic–pituitary–testicular axis (see figure to the right).[125] When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH. These latter two hormones stimulate the testis to synthesize testosterone. Finally, increasing levels of testosterone through a negative feedback loop act on the hypothalamus and pituitary to inhibit the release of GnRH and FSH/LH, respectively.

CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is sage, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.
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.
There is increasing interest in the group of patients who fail to respond to treatment with PDE-5 inhibitors and have low serum testosterone levels. Evidence from placebo-controlled trials in this group of men shows that testosterone treatment added to PDE-5 inhibitors improves erectile function compared to PDE-5 inhibitors alone (Aversa et al 2003; Shabsigh et al 2004).
Miscellaneous: Sleep: (REM sleep) increases nocturnal testosterone levels.[138] Behavior: Dominance challenges can, in some cases, stimulate increased testosterone release in men.[139] Drugs: Natural or man-made antiandrogens including spearmint tea reduce testosterone levels.[140][141][142] Licorice can decrease the production of testosterone and this effect is greater in females.[143]
A simple blood test can determine testosterone levels. There is a wide range of “normal” or healthy level of testosterone circulating in the bloodstream. The normal range of testosterone for men is between 250 and 1100 ng/dL for adult males, and between 8 and 60 ng/dL for adult females, according to the Mayo Clinic. Ask your doctor to test your testosterone levels if you have concerns about low testosterone (low T).
If PDE-5 inhibitors are not suitable or don’t work, other therapies include injections into the base of the penis, which cause flow of blood into the penis and a fairly immediate erection that lasts around an hour. The drugs injected are alprostadil (Caverject and Erectile dysfunctionex) and Invicorp (VIP and phentolamine). Alprostadil may also be inserted as a gel into the opening of the penis. This is not suitable if your partner is pregnant.

Type 2 diabetes is an important condition in terms of morbidity and mortality, and the prevalence is increasing in the developed and developing world. The prevalence also increases with age. Insulin resistance is a primary pathological feature of type 2 diabetes and predates the onset of diabetes by many years, during which time raised serum insulin levels compensate and maintain normoglycemia. Insulin resistance and/or impaired glucose tolerance are also part of the metabolic syndrome which also comprises an abnormal serum lipid profile, central obesity and hypertension. The metabolic syndrome can be considered to be a pre-diabetic condition and is itself linked to cardiovascular mortality. Table 1 shows the three commonly used definitions of the metabolic syndrome as per WHO, NCEPIII and IDF respectively (WHO 1999; NCEPIII 2001; Zimmet et al 2005).
Cross-sectional studies have not shown raised testosterone levels at the time of diagnosis of prostate cancer, and in fact, low testosterone at the time of diagnosis has been linked with more locally aggressive and malignant tumors (Massengill et al 2003; Imamoto et al 2005; Isom-Batz et al 2005). This may reflect loss of hormone related control of the tumor or the effect of a more aggressive tumor in decreasing testosterone levels. One study found that 14% of hypogonadal men, with normal digital rectal examination and PSA levels, had histological prostate cancer on biopsy. It is possible that low androgen levels masked the usual evidence of prostate cancer in this population (Morgentaler et al 1996). Most longitudinal studies have not shown a correlation between testosterone levels and the future development of prostate cancer (Carter et al 1995; Heikkila et al 1999; Stattin et al 2004) but a recent study did find a positive association (Parsons et al 2005). Interpretation of such data requires care, as the presentation of prostate cancer could be altered or delayed in patients with lower testosterone levels.

An international consensus document was recently published and provides guidance on the diagnosis, treatment and monitoring of late-onset hypogonadism (LOH) in men. The diagnosis of LOH requires biochemical and clinical components. Controversy in defining the clinical syndrome continues due to the high prevalence of hypogonadal symptoms in the aging male population and the non-specific nature of these symptoms. Further controversy surrounds setting a lower limit of normal testosterone, the limitations of the commonly available total testosterone result in assessing some patients and the unavailability of reliable measures of bioavailable or free testosterone for general clinical use. As with any clinical intervention testosterone treatment should be judged on a balance of risk versus benefit. The traditional benefits of testosterone on sexual function, mood, strength and quality of life remain the primary goals of treatment but possible beneficial effects on other parameters such as bone density, obesity, insulin resistance and angina are emerging and will be reviewed. Potential concerns regarding the effects of testosterone on prostate disease, aggression and polycythaemia will also be addressed. The options available for treatment have increased in recent years with the availability of a number of testosterone preparations which can reliably produce physiological serum concentrations.
When many people think of someone with a high level of testosterone, they may picture a man loaded with strength, sexual prowess, and machismo. But while high-T has been correlated with all those things, it’s also been correlated with aggression, sexual misconduct, and violence. One of testosterone’s most common uses—as a performance-enhancing steroid—illustrates both sides of the hormone. Injecting steroids can be a quick way for athletes to dramatically improve performance, but the side effects can also be extreme, and can include excessive body hair growth, sexual dysfunction, and the hard-to-corral anger known as “roid rage.”
Dr. Ronald Swerdloff, chief of the endocrinology division at the Harbor-UCLA Medical Center and a professor of medicine at UCLA's David Geffen School of Medicine, served on the panel of experts who developed the Endocrine Society's guidelines. He is also the principal investigator for one of the 12 sites of The Testosterone Trial in Older Men, a nationwide study funded mainly by the National Institute on Aging. The study of 800 men over age 65 with low testosterone is looking at whether men using AndroGel for one year, compared to placebo, will show improvements in walking speed, sexual activity, vitality, memory, and anemia. The study will be completed in June 2015.
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, nearly half showed no improvement with testosterone treatment. Many times, other health problems play a role in erectile difficulties. These can include: