Serum total and bioavailable testosterone levels, central obesity, and muscle strength changes with aging in healthy Chinese men

OBJECTIVES: To investigate the effects of the changes in serum bioavailable and total testosterone (TT) levels with aging on visceral body fat distribution and muscle strength in Chinese men. DESIGN: Cross-sectional study. SETTING: Ambulatory care. PARTICIPANTS: Four hundred seventy-five healthy ambulatory Chinese men (aged 18-89, body mass index (BMI) 16.4-40.0 kg/m(2)). MEASUREMENTS: Morning serum total and bioavailable testosterone levels, waist circumference (WC), waist-hip ratio (WHR), and right handgrip strength. RESULTS: Mean serum TT levels fell mildly but significantly with aging (P=.02, linear trend; one-way analysis of variance (ANOVA)), whereas mean serum bioavailable testosterone (BT) levels fell greatly with aging (P <.001, linear trend, one-way ANOVA). The rates of decline in serum TT and BT levels were 0.2% and 1.14% per year, respectively. [Correction added after online publication 14-May-2008: BT levels have been corrected from 1.44% to 1.14%.] After adjustment for adiposity according to BMI, multiple linear regression analyses showed that age remained significantly related to serum TT and BT levels. Handgrip strength decreased with age (correlation coefficient (r)=-0.394, P <.001) and was greater with higher serum BT levels (r=0.239, P <.001) but not with higher TT levels. WHR, before and after adjustment for BMI, was inversely related to serum TT (r=-0.34 and -0.197 respectively, P <.001) and BT levels (r=-0.104, P <.05 and -0.161, P <.001, respectively). CONCLUSION: In Chinese men, serum BT levels decreased with aging and may contribute to central obesity and poorer muscle strength in aging men.