Association of Testosterone and Sex Hormone-Binding Globulin With Metabolic Syndrome and Insulin Resistance in Men

OBJECTIVE - We sought to assess the associations of testosterones and sex hormone binding globulin (SHBG) with metabolic syndrome and insulin resistance in men. RESEARCH DESIGN AND METHODS - We defined metabolic syndrome according to the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. Among men aged >= 20 years who participated in the Third National Health and Nutrition Examination Survey (n = 1,226), the Cox proportional hazards model was used to estimate the prevalence ratio and 95% Cl of metabolic syndrome according to circulating concentrations of testosterones and SHBG. RESULTS - After adjustment for age, race/ethnicity, smoking status, alcohol intake, physical activity level, LDL cholesterol, C-reactive protein, and insulin resistance, men in the first quartile (lowest) (prevalence ratio 2.16 [95% Cl 1.53-3.06]) and second quartile of total testosterone (2.51 [1.86-3.37]) were more likely to have metabolic syndrome than men in the fourth quartile (highest, referent group) (P < 0.001 for linear trend). Similarly, men in the first quartile of SHBG (2.17 [1.32-3.56]) were more likely to have metabolic syndrome than men in the fourth quartile (P = 0.02 for linear trend). No significant associations of calculated free testosterone (P = 0.31 for linear trend) and bioavailable testosterone (P = 0.11 for linear trend) with metabolic syndrome were detected after adjustment for all possible confounders. CONCLUSIONS - Low concentrations of total testosterone and SHBG were strongly associated with increased likelihood of having metabolic syndrome, independent of traditional cardiovascular risk factors and insulin resistance.