Thyroxine Therapy in Euthyroid Patients Does Not Affect Body Composition or Muscular Function
Abstract
Objective: The main objective of the study was to evaluate the effects of small increments in thyroxine (T4) levels following levothyroxine (L-T4) administration on the body composition of women patients. The secondary objective was to assess the effect of the therapy on energy expenditure and muscular function. Methods: The prospective, randomized study consisted of a 12-month follow-up of 37 women with thyroid nodules. The patients were divided into two groups for comparison, one treated with L-T4 (20 women) and the other untreated (17 women). L-T4 dose was individually adjusted to obtain a serum thyroid-stimulating hormone in the lower portion of the normal range. Multiple tests, including bioelectrical impedance analysis, dual-energy X-ray absorptiometry, air displacement plethysmography, measurement of waist circumference, and skinfold anthropometry, were used to investigate the muscular, fat, and water compartments; energy expenditure and muscular function were assessed by cycle ergometry. Results: There were no significant differences in body composition, heart rate, energy metabolism, or muscular function between the group of women treated with L-T4 and the untreated group. Conclusion: The controlled increase of circulating T4 does not appear to modify the body composition or muscular function in women patients.