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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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