Testosterone - Men
Low levels of testosterone in men may contribute the development of insulin resistance and diabetes.[1-4] However, few studies have examined the association between testosterone levels and diabetes in men in the general population.
An interesting study was cunducted to test the hypothesis that low normal levels of total, free, and bio-available testosterone are associated with prevalent diabetes in men.
It is well-documented that testosterone levels decline with age in men.
After the age of 40 years, total testosterone decreases on average -4 ng/dL ( -0.124 nmol/L) per year  or 1.6% per year , and bioavailable testosterone by -2 to 3% per year. 
In older men (over 60 years of age), the average rate of decrement in total testosterone levels has been found to be 110 ng/dL every decade.
However, the relative contributions of changes in health and lifestyle to that decline have not been adequately evaluated. A notable study was set out to investigate this...
The objective of this study was to establish the relative importance of aging, health, and lifestyle in contributing to the testosterone decline in aging men.
Prediabetes is a condition in which blood glucose level is higher than normal but does not reach the level for diabetes diagnosis.[1, 2] Studies have shown that people with prediabetes tend to develop type 2 diabetes within 10 years, and are at increased risk for cardiovascular disease.
Among US adults over 18 years, the prevalence of prediabetes has increased from 29.2% in 1999 to 36.2% in 2010. Considering the entire US population in 2010 (approx. 309 million, data from US Cencus), this corresponds to 112 million US adults, or over one third of the US population.
Data from non-diabetic men have revealed an inverse association between insulin resistance and testosterone levels; i.e. a higher degree of insulin resistance is associated with lower testosterone levels.[4-6] This raises the question whether prediabetes, which is a state of increased insulin resistance, is also associated with low testosterone. However, few studies have investigated testosterone levels in men with prediabetes, and the risk of testosterone deficiency in men with prediabetes has not been reported.
Because the prevalence of prediabetes is affecting such a large number of Americans, and is on the rise, it is important to investigate how this condition might affect testosterone levels. Knowing that can help
detect men who are likely to have testosterone deficiency and might be at risk for health derangements caused by low-T.
"It is dangerous to be right when the government is wrong." - Voltaire
For reasons that are not readily apparent, there appears to be a conservative political movement that opposes the use of testosterone in older men. This was clearly demonstrated by the report of the Institute of Medicine, which felt that testosterone is not yet ready for prime time and that there is still a need for studies to prove its efficacy . Along the same lines, the guidelines of the Endocrine Society on testosterone use in older men seem to be ultra-cautious . But fortunately, there are also other, more liberal guidelines and recommendations [3-5].
Probably no other medical issue has been bombarded by the influx of “expert” views from all walks of life; from endocrinologists and psychiatrists to urological surgeons and gerontologists, from the lay press to the regulatory agencies and from the pharmaceutical to the entertainment industries. The dismal result of all this free-for all cacophony of opinions is a great deal of confusion, erroneous information and significant detriment to patients and physicians alike.
Let's take an in-depth look at the reasons for the negative attitudes to male testosterone replacement therapy (I will cover post-menopausal testosterone replacement in an upcoming article), and the hard scientific data that refutes it...
Study shows only a combination of testosterone therapy and strength training results in an increase in both mechanical muscle function and muscle mass (LBM).
To examine the effect of strength training and testosterone therapy on mechanical muscle function and lean body mass (LBM) in aging men with low-normal testosterone levels in a randomized, double-blind, placebo controlled 24-week study.
A notable study shows that men aged 20–79 who have low testosterone levels below 8.7 nmol/L (250 ng/dL) have a more than two-fold increased risk of mortality from all causes, compared with those with higher serum testosterone levels.
Importantly, this risk is independent of age, waist circumference, smoking habits, high-risk alcohol use, and physical activity.
This is an abstract from an interesting debate among leaders in the field of Testosterone and Men's Health.
Is there any unequivocal evidence that testosterone (T) can stimulate growth and aggravate symptoms in men with locally advanced and metastatic prostate cancer (PCa)?
This is not a controversial point: the answer is yes.
However, this evidence does not imply that PCa is a result of T or therapy with T (TTh) of hypogonadal men.
A few days ago, Jan 29th 2014, a controversial study  was published showing that men aged 65 years and older, had a two-fold increase in the risk of heart attack in the 90 days after filling an initial TT
prescription, regardless of cardiovascular disease history. Among younger men below 65 years of age with a history of heart disease, the study reported two to three-fold increased risk of MI in the 90 days following an initial TT prescription.
This study has stirred up heated discussions and media headlines. Let's dissect it and look under the hood...
Testosterone deficiency in men, aka hypogonadism, is associated with increased total and abdominal fat mass, and reduced muscle mass, which negatively impacts body composition.[1, 2] This contributes to development of risk factors like insulin resistance, chronic inflammation, and atherogenic dyslipidemia (a triad of increased blood levels of small, dense LDL particles and triglycerides, and decreased levels of HDL particles), which increase the risk for cardiovascular disease, metabolic syndrome and diabetes.[1, 3-16]
Previous studies have shown that testosterone replacement therapy ameliorates these risk factors in testosterone deficient (hypogonadal) men; it increases insulin sensitivity [17-20] and HDL (the "good" cholesterol) [9, 10, 20, 21], and reduces waist circumference [9, 20, 22], fasting blood glucose [9, 20] triglycerides (blood fats), LDL (the "bad" cholesterol) [19, 22-24], and several inflammatory markers.[17, 25]
A 2011 meta-analysis concluded that testosterone replacement therapy improves metabolic control, as well as reduces abdominal obesity. Many studies have shown that testosterone replacement therapy in hypogonadal men increases muscle mass and reduces fat mass.[19, 26-32] Further, adding testosterone (50 mg/day for 1 year, administered as a transdermal gel) to a diet and exercise program results in greater therapeutic improvements of glycemic control and reverses the metabolic syndrome.
Testosterone also has direct (non-obesity mediated) beneficial effects on many metabolic and cardiovascular risk factors [12, 33-37], and reduces death risk independently of body fat status. In line with all these effects, low testosterone levels are associated with increased risk of cardiovascular complications , and all-cause and cardiovascular disease death [40-42]. Low testosterone may thus be a predictive marker for men at high risk of cardiovascular disease. In a group of men aged 50-91 who were followed for 20 years, it was found that men whose total testosterone levels were in the lowest quartile (241 ng/dl or lower) were 40% more likely to die than those with higher levels, independent of age, adiposity, lifestyle or presence of cardiovascular risk factors.
Thus, treatment of testosterone deficient men with testosterone has demonstrated considerable health benefits. Despite this, critics state that most of the studies on testosterone replacement therapy were too small. They also argue that the studies were of too short duration (most of them lasting 6-12 months), and that the long-term effects of testosterone on body composition are not known.
Two 5 year long studies were just published that addressed the duration and small study size shortcomings in previous research...
We previously posted a commentary on the recently published and notoriously flawed study which concluded that TRT increases risk for heart attack.
This is the study which caused the media debates:
January 29th issue, the Scientific Journal PLOS (Public Library of Science) ONE published the article:
Here we have gathered commentaries from other medical professionals, all in one place: