Lean body mass is a major determinant of levothyroxine dosage in the treatment of thyroid diseases.
Total body weight is usually employed to calculate the amount of l-T(4) to be administered in patients with thyroid diseases. The aim of this study was to evaluate the effect of body composition on l-T(4) requirements. Body composition was assessed by dual energy x-ray absorptiometry in 75 patients on TSH-suppressive l-T(4) therapy after conventional thyroid ablation for differentiated cancer. The mean daily dose of l-T(4) was lower in normal-weight (127.5 +/- 21.3 mug/d) vs. overweight (139.4 +/- 24.5) and obese (151.3 +/- 29.1) subjects. There was a much stronger association between the l-T(4) dosage and lean body mass (P < 0.001, r = 0.667) compared with fat mass (P = 0.023, r = 0.26). Measurement of regional tissue composition showed peripheral lean mass as the best correlate with the dose of l-T(4) (r = 0.679, P < 0.001) whereas no correlation was observed with peripheral fat mass. In conclusion, individual l-T(4) requirements are dependent on lean body mass. Age- and gender-related differences in l-T(4) needs reflect different proportions of lean mass over the total body weight. An estimate of lean mass may be helpful to shorten the time required to attain a stable dose of l-T(4), particularly in subjects with high body mass index values that may be due either to increased muscular mass or to obesity.
Santini
Ferruccio
F
Department of Endocrinology, University of Pisa, 56124, Pisa, Italy. fsantini@endoc.med.unipi.it
Pinchera
Aldo
A
Marsili
Alessandro
A
Ceccarini
Giovanni
G
Castagna
Maria Grazia
MG
Valeriano
Rocco
R
Giannetti
Monica
M
Taddei
Donatella
D
Centoni
Roberta
R
Scartabelli
Giovanna
G
Rago
Teresa
T
Mammoli
Claudia
C
Elisei
Rossella
R
Vitti
Paolo
P
D001823:Body Composition; D005260:Female; D006801:Humans; D020738:Leptin / Q000097:blood; D008297:Male; D013851:Thinness; D013959:Thyroid Diseases / Q000188:drug therapy* / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000008:administration & dosage*
D020738:Leptin; D013972:Thyrotropin; D013974:Thyroxine