Effects of testosterone treatment on type 2 diabetes and
components of the metabolic syndrome
The metabolic syndrome is defined as glucose intolerance,
central obesity, dyslipidaemia (including increased triglycerides, decreased high-density lipoprotein cholesterol
concentration), hypertension, increased prothrombotic and
antifibrinolytic factors, and risk for atherosclerotic diseases
[32]. Low serum testosterone is common in men with type
2 diabetes and/or metabolic syndrome, and numerous studies have reported an inverse association between testosterone levels and obesity, insulin resistance and dyslipidemia.
This can partly be explained by an increase of aromatase
activity which is associated with a greater conversion of
testosterone to estradiol (testosterone–estradiol shunt associated with increased subcutaneous fatty-tissue) [33].
Moreover, hypogonadal men seem to have an increased
risk of developing type 2 diabetes mellitus and metabolic
syndrome [34, 35]. However, so far, only very small
placebo-controlled studies have investigated the effect of
testosterone replacement on insulin resistance and HbA1c.
Results are controversial with either no effect [36] or a
small beneficial effect [37]. Another effect of testosterone
replacement therapy is a decrease in total cholesterol,
mainly because of a decrease in HDL cholesterol levels
[12]. It is therefore too early to draw any conclusion about
the effect oftestosterone replacement on components ofthe
metabolic syndrome and large randomised controlled studies are needed