Objective: Low levels of testosterone in men have been shown to be associated with type 2 diabetes, visceral adiposity, dyslipidaemia and metabolic syndrome. We investigated the effect of testosterone treatment on insulin resistance and glycaemic control in hypogonadal men with type 2 diabetes.

Design: This was a double-blind placebo-controlled crossover study in 24 hypogonadal men (10 treated with insulin) over the age of 30 years with type 2 diabetes.

Methods: Patients were treated with i.m. testosterone 200 mg every 2 weeks or placebo for 3 months in random order, followed by a washout period of 1 month before the alternate treatment phase. The primary outcomes were changes in fasting insulin sensitivity (as measured by homeostatic model index (HOMA) in those not on insulin), fasting blood glucose and glycated haemoglobin. The secondary outcomes were changes in body composition, fasting lipids and blood pressure. Statistical analysis was performed on the delta values, with the treatment effect of placebo compared against the treatment effect of testosterone.

Results: Testosterone therapy reduced the HOMA index (-1.73±0.67, P=0.02, n=14), indicating an improved fasting insulin sensitivity. Glycated haemoglobin was also reduced (-0.37±0.17%, P=0.03), as was the fasting blood glucose (-1.58±0.68 mmol/l, P=0.03). Testosterone treatment resulted in a reduction in visceral adiposity as assessed by waist circumference (-1.63±0.71 cm, P=0.03) and waist/hip ratio (-0.03±0.01, P=0.01). Total cholesterol decreased with testosterone therapy (-0.4±0.17 mmol/l, P=0.03) but no effect on blood pressure was observed.

Conclusions: Testosterone replacement therapy reduces insulin resistance and improves glycaemic control in hypogonadal men with type 2 diabetes. Improvements in glycaemic control, insulin resistance, cholesterol and visceral adiposity together represent an overall reduction in cardiovascular risk.