Benefits · what the trials measured
What higher testosterone has been shown to do.
The sections below follow published trials: energy, muscle, bone, metabolism and sexual health. A result in a study is not a promise for every man.
“We aren't just trying to add years to your life; we are trying to add life to your years.”
“The good physician treats the disease; the great physician treats the patient who has the disease.”
When symptoms begin
Most European laboratories still treat roughly 8–12 nmol/L as the boundary of normality. The clinical literature places the onset of symptoms considerably higher. Scovell et al. showed that in young men, hypogonadal symptoms already appear at a total testosterone of 400 ng/dL (14 nmol/L), and Zitzmann et al. found the first symptoms around 15 nmol/L — with no clear-cut boundary, so some men are affected earlier than others.
- Lack of energy was the single strongest symptom predicting a total testosterone of 400 ng/dL (14 nmol/L) or below.
- Sadness, decreased strength and endurance, decreased ability to play sports and deterioration in work performance were also strongly predictive of low testosterone.
- Loss of libido and vigour became significantly more prevalent below 15 nmol/L (P < 0.001).
- Depression and type 2 diabetes — including in non-obese men — were significantly more common below 10 nmol/L.
- Cluster analysis grouped ageing men into three independent presentations: psychosomatic complaints, metabolic disorders, and sexual health problems.
“Lack of energy appears to be the most important symptom that predicts a total testosterone level of 400 ng/dL (14 nmol/L) or below.”
References
- Scovell J. M. et al., BJU Int 2015
- Zitzmann, Faber & Nieschlag, J Clin Endocrinol Metab 91: 4335–4343, 2006
Type 2 diabetes
Haider et al. followed 356 men with type 2 diabetes and testosterone below 350 ng/dL (12.1 nmol/L) for as long as 11 years in an observational registry; 178 of them were treated. Treated men showed reductions in fasting glucose, HbA1c and fasting insulin. Dhindsa and Dandona separately measured insulin sensitivity with a euglycaemic clamp in a small study and found tissue glucose uptake rose by roughly a third. Registries and small studies cannot prove cause and effect, and treatment is a decision for a physician.
- 34.3% of treated men achieved full remission of their diabetes; 46.6% achieved normal glucose regulation.
- 83% of the testosterone group reached the HbA1c target of 47.5 mmol/mol (6.5%) and 90% reached 53 mmol/mol (7%).
- No remissions were recorded in the untreated comparison group over the same period.
- Insulin-stimulated glucose uptake rose by 32–35% in a placebo-controlled clamp study.
- In the two-year randomised T4DM trial, diabetes was present at two years in about 12% of the testosterone group versus 21% on lifestyle alone.
“Testosterone therapy is potentially a novel additional therapy for men with type 2 diabetes and hypogonadism.”
References
- Haider et al., DOM 2020
- Dhindsa & Dandona, Diabetes Care 2016
- Wittert et al., T4DM, Lancet D&E 2021
Metabolic syndrome & the hypogonadal obesity cycle
Low testosterone can make it harder to hold on to muscle and body weight; fat mass rises, especially around the abdomen, and abdominal fat converts testosterone into estradiol, which can suppress production further. Researchers call this loop the hypogonadal obesity cycle. In observational registries of treated deficiency, waist circumference, glucose control and lipids improved together, but registries cannot prove cause and effect.
- Registries of treated deficiency reported lower waist circumference, triglycerides and blood pressure; registries cannot prove cause and effect.
- Abdominal fat converts testosterone into estrogen, which is one reason weight and hormones are assessed together.
- Some studies report lower fasting insulin and hs-CRP in treated deficiency; results vary.
- Long-term registries reported continued weight loss in some men; this is observational data, not a randomised result.
References
- Traish, World J Men's Health 2014
- Haider et al., DOM 2020
- Saad et al., registry data
Cardiovascular health
The cardiovascular evidence is mainly long-term observational: men whose deficiency is corrected and followed for years show a better risk profile than comparable untreated men, and controlled work in heart failure shows functional improvement rather than only laboratory change.
- Long-term registry follow-up shows improved lipid profile and blood pressure.
- Some observational studies associate treated deficiency with lower cardiovascular mortality; observational data cannot prove cause and effect.
- Endothelial function and exercise capacity improve in men with heart failure and low testosterone.
- Haematocrit must be monitored — erythrocytosis tracks the peak concentration, which is why dosing pattern matters.
References
- Traish 2014
- Sharma et al., Eur Heart J 2015
- Malkin et al., Eur Heart J 2006
Muscle mass & strength
Bhasin et al. suppressed the men's own production and then assigned graded weekly doses, which isolates the effect of the achieved blood level. The low doses did not simply give smaller gains — the 25 mg and 50 mg groups lost lean mass, gained body fat and remained symptomatic, with the 50 mg group sitting at about 306 ng/dL (10.6 nmol/L). The clear benefits appeared only once the achieved level moved above the normal range, and then rose dose-dependently.
- Fat-free mass fell and fat mass rose at 25 mg and 50 mg weekly — sub-therapeutic exposure made body composition worse.
- Gains in lean mass, leg strength and power increased progressively with higher achieved serum levels.
- The level reached, not merely 'being on therapy', decides the result.
- Lean mass has increased in treated deficiency; effects on muscle function in older men have been modest.
References
- Bhasin et al., NEJM 1996
- Bhasin et al., AJP-Endo 2001
Bone density & osteoporosis
Androgen deficiency is one of the treatable causes of male bone loss. In treated deficiency, bone mineral density has increased slowly, most clearly in the trabecular bone of the spine. Effects on fracture risk have not been established in trials.
- In long-term data, lumbar spine bone density increased; the size of the effect varies between studies.
- Bone density can improve with treatment of a confirmed deficiency; effects on fracture risk have not been established in trials.
- Effects on fracture risk have not been established in trials.
- Because bone loss is silent, measuring earlier can help find it sooner.
References
- Snyder et al., JCEM (BMD substudy)
- Traish 2014
Mood, motivation & well-being
The psychosomatic cluster is the one most often mislabelled as burnout. Zitzmann's cluster analysis treats it as a distinct presentation, and Scovell's data show energy and mood are the earliest signals — appearing before any laboratory value crosses a conventional cut-off.
- Lack of energy and sadness were among the strongest predictors of testosterone at or below 14 nmol/L.
- Depression was significantly more prevalent below 10 nmol/L, independent of obesity.
- In treated deficiency, some men report better drive and mood; effects vary and are often modest.
- Deterioration in work performance is a recognised, measurable symptom — not a character trait.
References
- Scovell et al., BJU Int 2015
- Zitzmann et al., JCEM 2006
- Zarrouf et al., J Psychiatr Pract 2009
Libido, erections & drive
Sexual health forms the third independent cluster. Loss of libido and vigour became significantly more common below 15 nmol/L, and the EMAS work showed the symptom burden tracks bioavailable hormone rather than the total number printed on a standard lab report.
- Loss of libido or vigour increased significantly below 15 nmol/L (P < 0.001).
- In the Testosterone Trials, sexual desire and activity improved modestly in older men with confirmed low testosterone.
- Symptom burden tracks free testosterone — which is why bioavailable hormone must be measured.
References
- Zitzmann et al., JCEM 2006
- Wu et al., EMAS, NEJM 2010
- Snyder et al., NEJM 2016
Ageing & longevity
Read together, the studies describe one physiology rather than eight separate conditions: the same hormonal decline shows up as fatigue in one man, a waistline in another and a fracture in a third. That is why symptoms attributed to 'age' can only be separated from an underlying, treatable cause by measuring.
- Several features of ageing — loss of muscle and bone, insulin resistance, inflammation, lower drive — overlap with the symptoms of androgen deficiency.
- Treatment is for confirmed deficiency, not a general anti-ageing measure.
- Because the decline is gradual, the symptoms are normalised long before they are investigated.
References
- Traish 2014
- Zitzmann et al., JCEM 2006
The hypogonadal obesity cycle
Type 2 diabetes and metabolic syndrome are downstream problems that researchers describe as a consequence of low testosterone. First it becomes difficult or impossible to maintain muscle mass and body weight; fat mass increases, especially around the abdomen — which then suppresses testosterone further. Researchers call this vicious circle the hypogonadal obesity cycle.
- 01Testosterone falls below the symptom threshold — energy, drive and training capacity decline first.
- 02Muscle mass becomes hard to maintain and resting metabolic rate falls.
- 03Fat mass increases, concentrated around the abdomen.
- 04Abdominal fat is rich in aromatase, converting testosterone into estradiol and suppressing the signal to produce more.
- 05Lower testosterone again — insulin resistance, higher fasting glucose and eventually type 2 diabetes.
In observational registries, some treated men with deficiency and type 2 diabetes reached remission, and the randomised T4DM trial found fewer cases of type 2 diabetes after two years with testosterone than with lifestyle measures alone. These results apply to men with confirmed deficiency. They do not mean that all men with type 2 diabetes should be treated, and higher doses are not better.
Find out where you actually sit.
None of this applies until you measure. Take the international symptom questionnaire, then confirm with an LC-MS/MS finger-prick test.