Leptin May Affect Hormonal Levels in Men

Males with anorexia nervosa have lower-than-normal testosterone levels, which leads to decreased sex drive and performance. When healthy weight is restored, testosterone increases and gender-related behaviors are normalized. In what is believed to be the first study to analyze the effects of serum leptin concentrations on reproductive function in anorectic men, German researchers report that leptin may play an important role in regulating the hypothalamic-pituitary-gonadal axis and fertility among underweight men, just as it does in underweight women.

Serum leptin levels charted during weight gain

Dr. Martin Wabitsch and colleagues measured serum leptin, luteinizing hormone, follicle-stimulating hormone, testosterone, and sex-hormone binding globulin among 3 men with anorexia nervosa every 2 weeks as the men regained weight (J Clin Endocrinol Metab 2000; 86:2982). At the time of referral, BMI values of the patients ranged from 12.5-17.3 kg/m2 and leptin levels ranged from below 0.03 mcg/l to 1.3 mcg/l. At the beginning of the study, the men’s serum leptin levels were below the 5th percentile. During weight gain, their leptin levels reached or passed the 95th percentile.

The temporal dynamics of body mass index and fat mass were closely related to serum leptin concentrations, and leptin increments were paralleled by increases in gonadotropins, testosterone, and the free androgen index (FAI). The authors noted that possible regulation of the hypothalamic-pituitary-gonadal axis in males with anorexia nervosa by leptin levels correlated with the finding that the changes of leptin levels over time were significantly correlated with those of gonadotropins, testosterone, and FAI.

It has also been shown repeatedly that androgens inhibit leptin production in adipose tissue and thus contribute to the gender differences in leptin levels. In the authors’ study, however, increasing testosterone levels did not lower leptin levels. This might be explained by strong overriding mechanisms associated with weight gain, that lead to an exaggerated leptin increment in anorectic patients.

The authors pointed out several drawbacks to their study beyond the small number of participants. The system that regulates fertility is very complex, much more so than is accounted for by the relatively simple hypothesis of this study. Also, one patient was clinically in a prepubertal stage, and those findings could not be directly related to fertility.