Dissociation of leptin and body weight in hyperthyroid patients after radioiodine treatment

OBJECTIVE: Leptin regulates energy production rates and body weight, which are frequently altered in hyperthyroidism. Data on a possible interaction b etween leptin and thyroid hormones are controversial. We assessed leptin se rum concentrations, BMI, proportional fat tissue mass and thyroid hormones in hyperthyroid patients in a long-term follow-up after radioiodine therapy . DESIGN: The study included 28 hyperthyroid patients (mean age 66 y) before and up to one y after radioiodine therapy. Leptin and thyroid hormones, gen eral parameters, BMI, proportional fat tissue (PFT) measurements by DEXA an d thyroid morphology were recorded. Twenty-four age-matched euthyroid indiv iduals (mean age 63 y) served as controls. RESULTS: At baseline, leptin concentrations were significantly decreased in all hyperthyroid patients as compared to controls. One year after radioiod ine therapy, 71% of the patients were euthyroid (group A) and 29% remained hyperthyroid (group B). BMI and PFT increased in both groups. While leptin concentrations remained low in group B, they normalised in group A after 6 to 12 months. Changes in leptin and thyroid hormone concentrations were pos itively correlated in group A patients (r = 0.49, P = 0.03) but not in pati ents remaining hyperthyroid. CONCLUSION: Our data indicate a dissociation in the regulation of plasma le ptin and BMI as well as proportional fat tissue in hyperthyroid patients wh ich may be attributable to differences in lean and adipose mass weight gain after radioiodine therapy or direct influences of thyroid hormones on lept in regulation.