Sex Difference in the Effect of Obesity on 24-Hour Mean Serum Gonadotropin Levels

To determine the effect of obesity on serum gonadotropin levels and any possible sex difference in the effect, we measured the 24-hour mean serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) concentrations in 62 healthy men with Body Mass Index (BMI) ranging from 20-94 and 61 healthy, regularly cycling women with BMIs ranging from 19-76. We also measured free testosterone (T) and estradiol (E2) in these subjects. There was a significant negative correlation between serum FSH and BMI in men: FSH(IU/L) = 49.9 × BMI - 0 . 5 6 7 ; r=-0.376, p=0.0026; but a significant positive correlation between serum FSH and BMI in women: FSH(IU/L)= 7.66 ′ 0.071 × BMI; r = 0.302, p = 0.018. Serum LH was weight-invariant in both sexes. In men, free T was negatively correlated with BMI: Free T(nmol/L)=0.74-0.0068 × BMI; r = 0.585, p = 0.0381; and free E2 was positively correlated with BMI: Free E2 (pmol/L) = - 1.03 ′ 0.057 × BMI; r = 0.50, p = 0.0014. In obese women as a group, free T was higher than in lean women (33 ′ 6.8 S.E.M. vs. 17.4 ′ 2.0 pmol/L; p < 0.0001), and free E2 was also higher than in lean women: (6.90 ′ 0.80 vs. 4.84 ′ 0.55 pmol/L; p = 0.046). Of the many cases of hypothalamic-pituitary hormonal dysregulation that have been reported in obesity, none has been studied for sex differences. Our results mandate that possible sex differences be investigated in all cases of dysregulation.