Serum leptin levels and bioelectrical impedance assessment of body composition in patients with Graves' disease and hypothyroidism

We investigated whether thyroid status modulates serum leptin concentration s and body composition as determined by bioelectric impedance analysis (BIA ). The percent body fat mass (%FM) in male Graves' disease was significantl y lower than that in age- and sex- matched normal subjects, at the levels o f 11.4+/-6.4% (mean+/-SD) vs 19.9+/-9.2% for men (n=12, P<0.05) but not for women (22.6+/-7.6% vs 24.9+/-13.1%, n=28). In contrast, in female hypothyr oidism (n=11) %FM was significantly higher than that in normal subjects (32 .9+/-11.5%, P<0.01). Among other body composition parameters, the percentag e of body water (%BW), and lean body mass (LBM) were significantly lower in hypothyroid patients, and the ECM (extracellular mass)/BCM (body cell mass ) ratio was significantly (P<0.0001) increased in Graves' disease which was the result of marked depletion of BCM with concomitant expansion of ECM. T he serum leptin levels were significantly decreased in male Graves' patient s (2.3+/-0.7 ng/ml, P<0.05), whereas in female Graves' patients (8.8+/-5.9 ng/ml) and patients with hypothyroidism (9.5+/-7.6 ng/ml), the levels were not different from those of normal controls matched for BMI or %FM. There w as a positive correlation between serum leptin levels and %FM in female Gra ves' patients (r=0.635, P=0.001) and in hypothyroid patients (r=0.801, P=0. 014) but not in male Graves patients. There was no significant relationship between serum leptin levels and thyroid hormones, TRab, or TSAb. In euthyr oid obese subjects there was a positive relationship between serum leptin l evels and serum TSH levels (r=0.37, P<0.01). These results suggest that hyp erthyroidism is characterized by the decreased fat mass and serum leptin le vels in men, but female patients appear to be resistant to the effect of th yroid hormones. Together with previous reports, thyroid status has a minor role in the regulation of serum leptin levels.