Several epidemiological studies have demonstrated a higher prevalence of low serum testosterone levels in men with type II diabetes mellitus. Recent work has shown that the majority have symptomatic hypogonadism and is not wholly attributed to a low level of sex hormone binding globulin. The major cause of morbidity and mortality in diabetic patients is coronary heart disease, which in turn is also associated with low levels of serum testosterone.
Insulin resistance is a major risk factor for atherosclerosis. Diet, exercise, insulin sensitisers such as metformin and thiazolidenediones has been shown to improve vascular risk factors. Treatment of insulin resistance has also been shown to reduce carotid artery intima media thickness.
Animal studies have demonstrated that testosterone enhances insulin sensitivity. There is a strong association between insulin resistance and visceral obesity. The potential mechanism by which testosterone acts as an insulin sensitiser will be discussed including the role of the adipocyte and the androgen receptor. We have recently completed a clinical trial on the effect of testosterone replacement therapy in hypogonadal men with type 2 diabetes. This study showed that insulin resistance, glycaemic control, waist-hip ratio and total cholesterol all significantly improved. Larger clinical trials will be required to investigate this further to determine whether or not TRT should be used routinely in hypogonadal diabetic men.
For review:- Androgens, insulin resistance and vascular disease in men. Kapoor D. et al, Clin Endocrinol 2005, 63; 239-250.
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