Determinants of sex hormone-binding globulin concentrations in a cross-sectional study of healthy men randomly selected

Abstract

Sex-hormone binding globulin (SHBG) is a glycoprotein synthesised in the liver and it is a transport protein which is primary modulator of the androgen signal. This cross-sectional study prompted us to investigate the relati-onship between SHBG and, age, anthropometric, body composition variables, the IGF-I system and leptin in a group of healthy adult men randomly selected. Included 134 men, aged 41.6 years, range 15-70 years. Body mass index (BMI) was calculated, and body composition was determined by a bioelectrical impedance analyser. Serum total IGF-I concentrations after acid-ethanol extraction, free IGF-I concentrations, IGFBP3, leptin, testosterone and SHBG were determined. Testosterone concentrations increased in the 2th decade and SHBG concentrations increased in the 4th decade. We observed an increase in leptin in the 4th decade with a decrease in IGF-I, free IGF-I and IGFBP3 throughout the decades. Total IGF-I correlated with waist/hip ratio; free IGF-I with BMI and waist/hip ratio and IGFBP3 did not correlated with any variable. As expected, there was a positive correlation between leptin and BMI, waist/hip ratio, fat free mass and fat mass. On the other hand, SHBG was negatively correlated with BMI, fat mass, total IGF-I, free IGF-I, IGFBP3 and leptin. Testosterone did not correlated with any anthropometric or body composition variable, IGF-I system components, leptin or SHBG. The multiple linear regression analysis produced a model that explained the 40.5% of SHBG variability; only fat mass and IGFBP3 brought an independent significant contribution to SHBG variability. In conclusion, in this population of healthy men randomly selected, we found that they had significant negative correlation between SHBG concentrations and anthropometric, body composition variables, the IGF-I system and leptin levels, and that fat mass and IGFBP3 may be the main determinants of SHBG changes.