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This article reviewed what is known about the consequences of low testosterone (also known as hypogonadism) in middle-aged and older men, with practical information on the benefits and risks of testosterone replacement. The authors examined evidence from a wide range of studies about low testosterone and its treatment to prepare their review.

This review discussed the relationship between low testosterone level and frailty in elderly men and evaluated the evidence which shows that testosterone replacement therapy improves the physical functioning and quality of life of elderly frail men with confirmed low testosterone levels.

This study compared the effects of the long-acting testosterone undecanoate injection with those of oral testosterone undecanoate capsules in 52 men (mean age 57 years) with hypogonadism (low testosterone) and symptoms of the metabolic syndrome (MetS) and/or type 2 diabetes mellitus. For the first 6 months of the study, two similar groups of men received either the testosterone injection every 12 weeks or testosterone undecanoate capsules twice daily. There was a third, control, group of men who received a dummy drug (placebo). After 6 months, the oral testosterone group was switched over to receive 6 months of treatment with the testosterone injection, while the other groups continued with their original treatment for another 6 months.

Testosterone replacement therapy with the long-acting injection formulation of testosterone undecanoate has been shown to return testosterone levels to normal and improve erectile function in European men with low testosterone (also known as hypogonadism) and erectile dysfunction (ED). However, there has been little information about how safe and effective the testosterone undecanoate injection is in Asian men. This study treated 133 Korean patients aged 42 to 75 years (average age 54 years) who had ED and low testosterone. The men received a series of three testosterone undecanoate injections; one at the start of the study then again after 6 and 18 weeks.

This study, published in the New England Journal of Medicine, identified the most important symptoms linked to late-onset hypogonadism (low testosterone levels in aging men) in a large group of men representative of the general population. When testosterone levels were also taken into consideration, having these three symptoms and low testosterone levels was a specific diagnosis of late-onset hypogonadism.

The TADTEST study examined whether adding testosterone replacement therapy could improve sexual function in men with erectile dysfunction (ED) who had not responded to the PDE5 inhibitor tadalafil, a prescription drug used to treat ED. It also investigated the effect that testosterone levels had on response to a PDE5 inhibitor to see if there was a threshold value for testosterone therapy to improve the effectiveness of PDE5 inhibitor therapy.

This study carefully evaluated available good quality studies that compared the levels of testosterone in men with or without the metabolic syndrome to see if metabolic syndrome is linked to low testosterone. The study also looked at the effects of testosterone replacement therapy on components of the metabolic syndrome.

The aim of this study was to examine whether long-term testosterone replacement therapy could help improve risk factors for heart disease and reduce narrowing of the arteries in men with low testosterone levels who also had metabolic syndrome and/or type 2 diabetes.

There is increasing evidence that erectile dysfunction may be a warning sign of a number of disease conditions, such as high blood pressure, metabolic syndrome, diabetes mellitus, depression and coronary heart disease.

Nearly 1700 men attending an andrology clinic for erectile dysfunction were monitored for an average of 4.3 years to find out whether those with low testosterone levels were more likely to suffer a major cardiovascular disease event, such as a heart attack or stroke.

A study in the United Kingdom observed 930 men with confirmed coronary artery disease over an average of nearly 7 years to find out how many had testosterone deficiency and to examine whether low testosterone affected survival.

In 2008 the International Journal of Impotence Research published a Norwegian study that examined whether lower than normal levels of the hormone testosterone in elderly men (average age 69) were linked to a reduced quality of life and physical and mental health. Researchers also studied whether treatment with supplementary testosterone could improve these conditions.

At the end of 2009 the American Journal of Andrology published the results of a clinical trial investigating the effects of diet and exercise (D&E) with and without the addition of testosterone given as gel absorbed through the skin, on 32 men with lower than normal levels of testosterone, and with recently diagnosed Type 2 Diabetes and indicators of potential heart disease (Metabolic Syndrome).

1493 patients from 23 countries joined this study; of these 1123 completed a series of five injections of supplementary testosterone.

All patients had lower than normal levels of testosterone at the start of treatment. The average age of men taking part was just over 49 years. Some suffered from other conditions such as hypertension (high blood pressure) and diabetes.

The findings of this study were presented to the Men’s Health World Congress, 2010 held in France.

A clinical study published in the European Journal of Endocrinology has shown that treatment (injections) with supplementary testosterone (Nebido®) enabled men with low testosterone levels who suffer from angina to exercise for longer before feeling uncomfortable.

Men in the group also lost weight, although not to a significant extent, compared to a similar, well matched group of men not receiving the treatment (the placebo group).

This is the longest study investigating testosterone therapy in patients with long term (or chronic) angina.

A Russian study, published in the Journal of Sexual Medicine in July 2010, looked at how men with metabolic syndrome (Met S) and hypogonadism responded to treatment with either a placebo (safe, dummy medicine) or testosterone (Nebido®) injections.

Aging is associated with a reduction in testosterone levels in the blood. This reduction causes a number of symptoms, one of which is losing muscle mass.

This small, well-designed 12-month study looked at the effect of the testosterone patch on body composition and hormones in 60 men aged ≥55 years who were healthy and not obese, and who had low-to-normal testosterone levels and typical testosterone deficiency symptoms.

Chronic heart failure (CHF) is a medical condition where the heart cannot pump enough blood around the body. This can lead to muscle weakness. Common symptoms include shortness of breath and inability to exercise. Many patients with CHF also have low testosterone levels and studies have suggested that testosterone treatment may improve some symptoms of CHF.