Serum leptin in overt and subclinical hypothyroidism: effect of levothyroxine treatment and relationship to menopausal status and body composition.
BACKGROUND
The relationship between thyroid status, including subclinical hypothyroidism (SH) and serum leptin is controversial or uncertain. Therefore we evaluated serum leptin in SH and overt hypothyroidism (OH) and determined the effects of levothyroxine (LT(4)) replacement on serum leptin in these disorders.


METHODS
Serum leptin, thyrotropin (TSH), free thyroxine, insulin, glucose, and body composition parameters were compared in 55 SH, 20 OH, and 28 euthyroid (EU) pre- and postmenopausal women. In addition, the effect of LT(4) treatment on serum leptin in SH and OH was assessed.


RESULTS
The mean +/- SD (median) serum leptin concentrations in the OH and SH groups were higher than in the EU group (35.1 +/- 27.2 [33.0] and 36.6 +/- 21.9 [30.6] ng/mL, respectively, vs. 23.2 +/- 19.3 [17.9] ng/mL, p = 0.011), but the difference was only significant in postmenopausal women. The body mass index (BMI), fat mass index (FMI), and the homeostasis model assessment-insulin resistance (HOMA-IR) index values were not different among these groups. In premenopausal women there was no correlation between leptin, BMI, or FMI and serum TSH levels (r(s) = 0.009, p = 0.474; r(s) = 0.043, p = 0.367; r(s) = 0.092, p = 0.232). In the postmenopausal women, the partial correlation coefficient between TSH and leptin was present, even when controlling for BMI (r(s) = 0.297, p = 0.042) and FMI (r(s) = 0.275, p = 0.050). LT(4) treatment was associated with a reduction of serum leptin concentrations in the OH group (p = 0.008). In SH group there were no differences between LT(4) replacement or no treatment, since a fall in serum leptin levels was detected in both SH subgroups, despite a more pronounced fall with LT(4) use. Treatment of the SH and OH groups with LT(4) did not influence HOMA-IR index or body composition.


CONCLUSIONS
Serum leptin concentrations are elevated in postmenopausal women with SH or OH. A relationship between thyroid status and serum leptin is further supported by the fact that LT(4) treatment, to restore the EU status, reduced serum leptin levels in OH in the absence of significant effects on BMI. In women, hypothyroidism influences either leptin secretion or degradation and this effect is more pronounced in postmenopausal than in premenopausal women.
Endocrinology Service, Clementino Fraga Filho University Hospital, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. pfatima@hucff.ufrj.br
Patrícia F S
PF
Teixeira
Mônica D
MD
Cabral
Nathalie A
NA
Silva
Débora V
DV
Soares
Valéria B
VB
Braulio
Ana Paula C B
AP
Couto
Jodélia L M
JL
Henriques
Antônio J L
AJ
Costa
Alexandru
A
Buescu
Mário
M
Vaisman
D000328:Adult; D001786:Blood Glucose / Q000187:drug effects; D001823:Body Composition; D003430:Cross-Sectional Studies; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000188:drug therapy* / Q000503:physiopathology; D007328:Insulin / Q000097:blood; D020738:Leptin / Q000097:blood*; D008875:Middle Aged; D017698:Postmenopause / Q000097:blood*; D017697:Premenopause / Q000097:blood*; D011446:Prospective Studies; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000627:therapeutic use*; D013997:Time Factors; D016896:Treatment Outcome
D001786:Blood Glucose; D007328:Insulin; D020738:Leptin; D013972:Thyrotropin; D013974:Thyroxine