Testosterone Treatment Improves Insulin Resistance in Japanese MaleMetabolic Syndrome

The metabolic syndrome involves a cluster of clinical features including visceral obesity, insulin resistance, hypertension, glucose intolerance, and dyslipidemia. Recent studies have shown that low testosterone levels are significantly associated with metabolic syndrome and type 2 diabetes. We examined the change in insulin resistance after testosterone treatment in five Japanese men with metabolic syndrome and low free testosterone levels (age : 50.2 ± 8.7 yrs, BMI : 30.5 ± 5.0, waist : 97 ± 7 cm ; Mean ± SD). Testosterone supplements were administered by intramuscular injection (250 mg every 2 weeks) for 3 to 6 months. Fasting plasma glucose (FPG), fasting serum insulin (F-IRI), HbA1c, total cholesterol(TCHO), triglyceride(TG), HDL-C, LDL-C, free testosterone, LH, FSH, BMI and waist circumference were measured. We used homeostasis model assessment (HOMA-R) as an index of insulin resistance and investigated the change in insulin resistance after testosterone treatment. Average results before treatment were as follows: BMI 30.5 ± 5.0, waist 97 ± 7 cm, FPG 112 ± 6 mg/dl, F-IRI 25.1 ± 8.5 μIU/ml, HOMA-R 7.0 ± 2.7, HbA1c(NGSP) 5.8 ± 0.3%, TCHO 227 ± 31 mg/dl, TG 185 ± 64 mg/dl, HDL-C 43 ± 9 mg/dl, LDL-C 149 ± 37 mg/dl, free testosterone 5.9 ± 1.0 pg/ml, LH 1.7 ± 0.6 IU/ml, FSH 3.7 ± 0.7 IU/ml. After treatment, F-IRI, HOMA-R, TCHO and LDL-C were significantly decreased to 12.9 ± 3.6 μIU/ml, 3.3 ± 1.1 199 ± 29 mg/dl and 120 ± 31 mg/dl, respectively. Free testosterone was significantly increased to 8.5 ± 0.6 pg/ml. Other parameters were not changed significantly. In conclusion, these results suggest that testosterone treatment improves insulin resistance in Japanese men with metabolic syndrome and low free testosterone levels.