Total, free and bound leptin and thyroid function in elderly women with different body weights

Objective The present study was aimed at evaluating the relationship of total leptin, and its free leptin (FL) and bound leptin (BL) fractions with adipose mass in very old euthyroid women, in relationship to thyroid function. Subjects and methods Twenty‐five older women (age: 73–95 years) were studied. Subjects representing underweight, normal weight and overweight/obese conditions were included. Plasma leptin, TSH, free T₄ (FT₄) and free T₃, (FT₃) total and HDL cholesterol were measured. FL and BL were evaluated by Fast Protein Liquid Chromatography (FPLC) analysis. Results Plasma leptin concentration was positively correlated with body mass index (BMI) (r = 0·64, P = 0·0005) and tricipital skin‐fold thickness (TF) (r = 0·46, P = 0·0187). Leptin was positively correlated with TSH (r = 0·50, P = 0·0116) and inversely with FT₃ (r = –0·40, P = 0·0477). TSH correlated with the adiposity indexes BMI (r = 0·40, P = 0·05) and TF (r = 0·42, P = 0·0336). Plasma FT₃ was positively correlated with FT₄ (r = 0·49, P = 0·012). FL and BL were evaluated in 8 out of 25 subjects. FL positively correlated with BMI (r = 0·81, P = 0·0218) and leptin (r = 0·83, P = 0·0004), whereas BL did not correlate with these parameters. Conclusions The present results indicate that in very old women, plasma leptin concentrations reflect the extent of adipose mass and suggest that a complex regulatory interaction exists between leptin and thyroid function, possibly taking place at central (hypothalamus–pituitary) and peripheral (deiodinase activity) levels.