Low testosterone levels are a common finding in men with coronary artery disease and Type 2 diabetes and predict the future development of the metabolic syndrome and Type 2 diabetes in healthy men. Testosterone replacement therapy has been shown to improve insulin sensitivity and glycaemic control in men with diabetes and improves numerous other cardiovascular risk factors. Interest in testosterone as a potential treatment for cardiovascular disease continues to grow. Low HDL cholesterol (HDL-C) levels are now recognised as an independent cardiovascular risk factor and comprise part of the metabolic syndrome. The effect of testosterone treatment on HDL-C in clinical trials has been inconsistent. Testosterone may be acting through differing processes with opposite effects on HDL.
We present data on the link between testosterone levels and blood lipid levels in a sample of 293 men with Type 2 diabetes. Lipids were assessed by standard methods. Total testosterone (TT) and SHBG levels were assessed by ELISA. Bioavailable testosterone (BioT) was measured by ammonium precipitation. Calculated bioavailable (cBioT) and free testosterone (cFT) were also derived using recognised formulae.
Regression analysis revealed that HDL-C levels were positively associated with TT (regression coefficient r=0.253, P<0.001), BioT (r=0.172, P=0.003), cBioT (r=0.219, P=<0.001), cFT (r=0.139, P=0.18) and SHBG (r=0.169, P=0.004). Total cholesterol levels were not significantly associated with testosterone levels but there was a trend towards a negative association of testosterone with total cholesterol (P=0.051).
Thus, in our group of men with Type 2 diabetes, testosterone is positively associated with HDL-C suggesting that the dominant effect of testosterone in this group may be to increase HDL. Further clinical trials of testosterone replacement therapy in men with type 2 diabetes are warranted.