Serum thyrotropin is correlated with body
mass in obese women with normal thyroid function
(July 2005)
The background of the study. Thyroid dysfunction
is associated with changes in the metabolism of adipose tissue.
This study was done to determine the relationships between thyroid
function, body weight, insulin sensitivity, and the secretion of
leptin, a hormone produced by adipose tissue that reduces appetite,
in obese, euthyroid women.
How the study was done. The study subjects were
87 women with long-standing obesity (body-mass index [BMI], >30
kg/m2). All had normal thyroid function, normal serum antithyroid
antibody concentrations, normal glucose tolerance, and normal serum
lipid concentrations. Fat mass and fat-free mass; resting energy
expenditure; serum thyrotropin (TSH), free thyroxine (T4), and free
triiodothyronine (T3); serum insulin and leptin; and insulin sensitivity
were measured in each woman.
The results of the study. The BMI was <40 kg/m2
in 54 percent and ≥40 kg/m2 (morbid obesity) in 46 percent.
Serum glucose concentrations, after both an overnight fast and oral
glucose administration, were normal in both groups, but fasting
serum insulin concentrations were higher and insulin resistance
was greater in the women with a BMI ≥40 kg/m2. Serum TSH concentrations
were correlated with BMI and also with serum leptin, but serum free
T4 and free T3 concentrations were not correlated with any of these
measures.
The conclusions of the study. Among healthy obese women with normal
thyroid function, serum TSH concentrations are higher (within the
normal range) in those with higher body mass and higher serum leptin
concentrations, suggesting that leptin may play a role in regulating
TSH secretion.
The original article. Iacobellis G, Ribaudo MC,
Zappaterreno A, Iannucci CV, Leonetti F. Relationship of thyroid
function with body mass index, leptin, insulin sensitivity and adiponectin
in euthyroid obese women. Clin Endocrinol (Oxf) 2005;62:487-91.
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