Effect of subclinical hypothyroidism on body fluid compartments

Objective: The present study was aimed to assess the effects of subclinical hypothyroidism on body composition IBC). Subjects: Thirty-one women (age: 37 +/- 9.9 years) with a wide range of body mass index (BMI) were studied. Subclinical hypothyroidism was defined by a basal TSH greater than or equal to 4 mU/L and/or TRH stimulated peak greater than or equal to 30 mU/L. Mea surements: For each subject, weight, height, BMI, multifrequency bioelectri cal impedance spectroscopy (BIS) and D2O and NaBr dilution tests were perfo rmed to assessed total body water (TBW) and extracellular water (ECW). Thyr oid function (basal and TRH stimulated TSH, free T3, and free T4) were dete rmined from fasting blood samples for all subjects. Total body dual energy X-ray absorptiometry (DXA) were used to measure fat mass (FM) and lean mass (Lean). Results: The results of BIS were compared with the TBW and ECW est imated by the dilution techniques on the same individuals. The correlation was R-2 = 0.65 for impedance at 5 kHz and ECW by NaBr and R-2 = 0.72 for im pedance at 100 kHz and TBW by D2O. Intracellular water (ICW) was calculated as differences between TBW and ECW measured by dilution methods. Percent o f ECW and ICW were related to BMI (ANOVA, p < 0.001). No difference in TBW, body water distribution and body composition related to thyroid function w as demonstrated. Conclusions: In our patients affected with subclinical hyp othyroidism, with or without obesity, only obesity appeared related to TBW, ECW and ICW: the subclinical hypothyroidism, on the contrary, had no effec t on compartments of body fluids. Bioimpedance is a valid tool to assess bo dy fluid distribution in subclinical hypothyroidism.