Plasma leptin concentrations in relation to sick euthyroid syndrome in elderly patients with nonthyroidal illnesses

Leptin, the ob gene product, seems to be involved in regulating energy expenditure in humans, but its role in the pathophysiology of the energy imbalance in chronically ill patients is largely unknown.

To evaluate plasma leptin concentrations and thyroid function in elderly patients with nonthyroidal illnesses (NTI).

Sixty-four NTI elderly patients (75.0 +/- 6.3 years, 27 males and 37 females) and 21 age- and sex-matched healthy controls (73.0 +/- 5.5 years, 9 males and 12 females) were enrolled in the study. In all subjects tri-iodothyronine (T(3)), thyroxine (T(4)), reverse T(3) (rT(3)), free T(3) (fT(3)), free T(4) (fT(4)), TSH, and plasma leptin concentrations were measured. Nutritional status was also evaluated in all subjects studied by the measurement of body mass index (BMI), lymphocytes, serum iron, hemoglobin, plasma albumin, transferrin and total cholesterol.

The data on thyroid hormones enabled us to identify three groups: group A, subjects (15 patients) with T(3) and fT(3) levels comparable to those of controls; group B, subjects (25 patients) with T(3) and fT(3) levels lower than controls and rT(3) levels comparable to those of controls; group C, subjects (24 patients) with T(3) and fT(3) levels lower than those of controls and high rT(3) levels. The patients of group C showed lower plasma leptin levels than the controls, 6.6 (5.5-14.2) and 16.3 (7.2-23.7) ng/ml (median with interquartile range in parentheses, p < 0.05), respectively. Females also showed higher plasma leptin levels than males in the controls, group A and group B, but not in group C. Moreover, plasma leptin concentrations were directly correlated to BMI in all the groups studied, while a negative correlation between leptin and rT(3) was detectable in group C (r = -0.44, p < 0.05), also after adjusting for BMI and sex.

The concurrence of modifications in plasma leptin and thyroid hormones concentrations found in elderly NTI patients with a sick euthyroid syndrome could reflect a particular neuroendocrine status, leading to a reduction in the catabolic processes in the course of chronic diseases.