BIOELECTRICAL-IMPEDANCE ASSESSMENT OF BODY-COMPOSITION IN THYROID-DISEASE

To assess the metabolic effects of thyroid disease, body composition w as determined by bioimpedance analysis (BIA) in 72 patients with untre ated hyperthyroidism (mean age 48.7 +/- 1.9 years) and 26 patients wit h untreated hypothyroidism (63.8 +/- 3.4 years), Bioelectrical whole b ody resistance (R) and reactance (Xc) were used for computerized calcu lation of lean body mass (LBM), body cell mass (BCM), extracellular ma ss (ECM) and body fat (BF). Compared with age- and sex-matched healthy controls the most sensitive parameter indicating excess thyroid hormo ne was the ECM/BCM ratio which was markedly elevated in all hyperthyro id subjects. ECM/BCM alteration resulted from marked depletion of BCM with concomitant expansion of ECM. BCM change is thought to be predomi nantly due to a loss of muscle mass while ECM rise may reflect an incr ease in extracellular fluids. In contrast, hypothyroidism was characte rized by an increase in BF besides a relatively unaffected LBM compone nt. Serum parameters of thyroid function (tri-iodothyronine (T-3), fre e thyroxine, TSH) did not correlate with the determinants of body comp osition except for a slight inverse relationship between the phase ang le (Xc/Rx180 degrees/pi) and T-3 concentration in Graves' disease pati ents, We conclude that hyperthyroidism is primarily accompanied by qua ntitative as well as qualitative changes in the lean body while consid erable fat increase is the most important feature of hypothyroidism. S everity of body composition derangement cannot be predicted from the d egree of thyroid dysfunction, BIA could become a useful tool which all ows objective determination of even subtle metabolic manifestations of thyroid disease and should, therefore, complement conventional clinic al and biochemical assessment.