Testosterone deficiency is common in men with type 2 diabetes. Limited evidence suggests that low testosterone is associated with insulin resistance, but the prevalence of low testosterone levels in men with type 1 diabetes is unknown. Grossmann and colleagues, therefore, conducted a cross-sectional study to determine the prevalence of testosterone deficiency and examine the relationship between testosterone levels and insulin resistance in 574 men with type 2 diabetes and 69 with type 1 diabetes.
Fasting blood samples were collected in the morning for determination of total testosterone (TT) levels, indices of insulin resistance and calculated free testosterone (cFT; adjusted for sex-hormone-binding globulin). TT and cFT levels of a randomly selected subgroup of 262 men with type 2 diabetes were retested after a median of 6 months.
Interestingly, 43% of men with type 2 diabetes had low TT levels (<10 nmol/l or <288 ng/dl), whereas the prevalence was only 7% for men with type 1 diabetes. However, one in five men with type 1 diabetes had low cFT levels (<0.23 nmol/l or <6.6 ng/dl), a prevalence similar to that of men with type 2 diabetes after adjustment for age and BMI. After adjustment for confounders including age and BMI, low testosterone levels were independently associated with insulin resistance in both groups. Furthermore, changes in TT level and insulin resistance were inversely correlated in the longitudinal analysis.
The authors caution that testosterone replacement therapy should only be recommended for affected men if randomized trials confirm its overall benefit.
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Low testosterone levels are associated with insulin resistance in men with diabetes. Nat Rev Endocrinol 4, 360 (2008). https://doi.org/10.1038/ncpendmet0848