Testosterone therapy preserves muscle strength and power in aging men with type 2 diabetes—a randomized controlled trial

The purpose of the study was to evaluate whether testosterone replacement therapy improves muscle mechanical and physical function in addition to increasing lean leg mass and total lean body mass in aging men with type 2 diabetes and lowered bio-available testosterone (BioT) levels. Thirty-nine men aged 50-70years with type 2 diabetes and BioT levels <7.3nmol/L were included from an academic tertiary-care medical center. Patients were randomized to testosterone gel (testosterone replacement therapy, n = 20) or placebo (n = 19) for 24weeks, applying a double-blinded design. Muscle mechanical function was assessed by Nottingham Leg Rig (leg extension power) and isokinetic dynamometry (knee extensor maximal isometric contraction, rate of force development (RFD100), maximal dynamic contraction (Dyn180)). Physical function was assessed by gait speed. Body composition was assessed by whole body dual-energy X-ray absorptiometry (total lean body mass, lean leg mass, total fat mass, leg fat mass). Levels of total testosterone (TotalT), BioT, free testosterone (FreeT), and sex hormone-binding globulin were measured from fasting blood samples. Coefficients (b) represent the placebo-controlled mean effect of intervention. Maximal isometric contraction (b = 18.4 Nm, p = 0.039), RFD100 (b = 195.0Nm/s, p = 0.017) and Dyn180 (b = 10.2 Nm, p = 0.019) increased during testosterone replacement therapy compared with placebo. No changes were observed in leg power or gait speed. Total lean body mass (b = 1.9kg, p = 0.001) and lean leg mass (b = 0.5kg, p<0.001) increased, while total fat mass (b = -1.3kg, p = 0.009) and leg fat mass (b = -0.7kg, p = 0.025) decreased during testosterone replacement therapy compared with placebo. Total T (b = 14.5nmol/L, p = 0.056), BioT (b = 7.6nmol/L, p = 0.046), and FreeT (b = 0.32nmol/L, p = 0.046) increased during testosterone replacement therapy compared with placebo, while sex hormone-binding globulin (n = -2nmol/L, p = 0.030) decreased. Knee extensor muscle mechanical function was preserved, and body composition improved substantially during testosterone replacement therapy for 24weeks compared with placebo, whereas physical function (gait speed) was unchanged in aging men with type 2 diabetes and lowered BioT levels.