Small doses of triiodothyronine can change some risk factors associated with abdominal obesity

Abstract

OBJECTIVE: To elucidate whether the administration of small doses of triidothyronine (T3) can increase concentrations of sex hormone binding globulin (SHBG) in obese women with different types of obesity and to evaluate the potential metabolic benefits of such treatment. DESIGN: Daily administration of 20 μg of T3 during six weeks while maintaining habitual food intake and physical activity. SUBJECTS: Seventy premenopausal obese women (age: 41.2±1.5 y mean±s.e.m., body mass index (BMI): 34.4±0.7). MEASUREMENTS: Plasma concentrations of SHBG, lipids, insulin, thyroid hormones, sex hormones, blood glucose and insulin sensitivity (by euglycemic insulin clamp in 12 patients) at base line after six weeks of treatment. RESULTS: Six weeks treatment with small doses of T3 resulted in a significant increase in plasma SHBG. The increase of SHBG was higher in abdominal obesity and not associated with a significant change in body weight, plasma insulin concentration, insulin/glucose ratio of plasma insulin sensitivity (glucose disposal during insulin clamp). In patients with initially high SHBG the significant increase of insulin removal (as judged from the increase of c-peptide/insulin ratio) was observed. Treatment resulted in a reciprocal increase of T3, decrease of thyroxine (T4), and a more than double increase of T3/T4 ratio. CONCLUSIONS: Administration of small doses of T3 can increase the concentration of SHBG without changing insulin concentrations or sensitivity. As there was a significant decrease (by 36%) of T4 and parallel increase of T3 with a clear increase of T3/T4 ratio it seems possible that rather than lack of thyroid hormones a lower peripheral deiodination of T4 might be a factor contributing to the low SHBG concentration in abdominal obesity. Treatment with small doses of T3 may be considered to ameliorate some of the risk factors associated with abdominal obesity, particularly in some subgroups of obese women with a relative resistance to thyroid hormones possibly dependent on decreased peripheral deiodination of thyroxine.