The relationship between serum levels of insulin and sex hormone-binding globulin in men: the effect of weight loss

Abstract

It is known that there is an inverse relationship between the serum levels of insulin and sex hormone-binding globulin (SHBG) in women, but the relationship in men has not been reported. It is not known whether changes in the one cause changes in the other, or whether they change in opposite directions in response to some third factor. Because obesity raises insulin levels and lowers SHBG levels in both sexes, we proposed to study the cause-effect question by determining whether the relationship between changes in SHBG and insulin levels during active weight loss. We studied 70 healthy weight-stable men with body mass index (BMI) from 20.7-94 (normal, 22.5 +/- 2.5) and restudied 17 of them during diet-induced weight loss. Fasting serum insulin levels in the weight-stable men showed a positive linear correlation with BMI, increasing 1 microU/mL per unit increase in BMI (P < 0.0001). SHBG levels in the weight-stable men showed a negative linear correlation with BMI, decreasing 0.2 nmol/L per unit increase in BMI (P < 0.0002). In the weight-stable men, there was an inverse hyperbolic correlation between SHBG and insulin levels; SHBG (nmol/L) = 13.1 + [30.1 divided by insulin (microU/mL)] (P < 0.002). During weight loss, insulin levels decreased at an average rate of 6.1 microU/mL per unit decrease in BMI, a much higher slope than the positive slope vs. BMI in weight stable men. During weight loss, SHBG levels increased at an average slope of 0.43 nmol/L per unit decrease in BMI,…