Inverse association between serum insulin and sex hormone-binding globulin in a population survey in Sweden

OBJECTIVES Obesity is associated with low levels of sex hormone-binding globulin (SHBG). While the reason is not fully understood, we aimed to study the association between serum insulin and levels of SHBG in a random population. DESIGN AND METHODS Between 2001 and 2005, a random sample of 2816 participants aged 30-74 years were enrolled in a cross-sectional survey in the South-west of Sweden. Fasting blood samples were collected and an oral glucose tolerance test (OGTT) was conducted in all subjects without known diabetes. Diabetes mellitus was defined according to criteria from WHO, and clinical characteristics were used to discriminate between type 1 (T1D) and type 2 diabetes (T2D). Analyses of SHBG were successful in 2782 participants (98%), who thus constituted the current study population. RESULTS WE FOUND SIGNIFICANT INVERSE ASSOCIATION BETWEEN LEVELS OF SHBG AND FASTING SERUM INSULIN IN BOTH GENDERS (MEN: β=-0.090, P=0.001; women: β=-0.197, P<0.001), which was independent of differences in age and BMI. The associations remained when also differences in fasting plasma glucose were accounted for (men: β=-0.062, P=0.022; women: β=-0.176, P≤0.001). Subjects with T1D exhibited higher levels of SHBG than both T2D (men: δ=15.9 nmol/l, P<0.001; women: δ=71.1 nmol/l, P<0.001) and non-diabetic subjects (men: δ=15.1 nmol/l, P<0.001; women: δ=72.9 nmol/l, P<0.001) independent of age, BMI and fasting glucose levels. CONCLUSION These findings are consistent with high levels of SHBG in T1D, and correspondingly low levels in T2D subjects, suggesting an inhibitory effect of insulin on the SHBG production in the liver.