Evidence for hypogonadism in massively obese males due to decreased free testosterone.

In obese male subjects with 160 - 200% of ideal body weight (IBW = 100%) the decrease in total plasma testosterone is biologically ineffective since SHBG is concomitantly decreased from 30.0 +/- 3.6 to 20.0 +/- 3.4 nM/l. Conversely, in massively obese males with greater than 250% of IBW, the decrease in SHBG (to 10.6 +/- 1.8 nM/l) is too small to compensate for total testosterone decrease (from 6.04 +/- 0.57 to 1.72 +/- 0.32 ng/Ml). Therefore, free testosterone is markedly less in the massively obese patients (55 +/- 8 vs. 127 +/- 15 pg/ml in the controls). Despite this significant difference in free testosterone concentrations (p less than 0.01), plasma LH is even lower in the obese (6.8 +/- 0.8 mU/ml) than in the controls (10.0 +/- 1.0 mU/ml). This may be an effect of free estradiol, which rises from 0.48 to 1.52 pg/ml in the massively obese subjects. These alterations are clearly demonstrated by the imbalance of the estradiol/testosterone ratios, which increase 10-fold and 7-fold for the total and for the free sex hormones, respectively. We conclude that the decrease in SHBG, which prevents obese males from developing hypogonadism, is not sufficiently effective in the massively obese patients to compensate the marked decrease in testosterone. This, in connection with the observed increase of free estradiol, may cause hypogonadism and hyperestrogenism in these subjects.