Effects of thyrotrophin, thyroid hormones and thyroid antibodies on metabolic parameters in a euthyroid population with obesity

Objective To investigate whether thyroid function in the euthyroid range and thyroid autoimmunity status would affect metabolic measures in individuals with obesity. Design Cross-sectional. Patients We retrospectively evaluated 5300 consecutive obese (BMI >= 30 kg/m(2)) subjects attending the Obesity Outpatient Clinic. Subjects with overt or subclinical thyroid disease, diabetes mellitus, chronic disease or using any medication were excluded. After exclusion, 1275 euthyroid [TSH values >0.4 and <4.5 mu IU/ml, free triiodothyronine (FT3), free thyroxine (FT4) in the normal reference range] obese subjects (aged 18-65 years) were eligible for the study. Measurements The physical and biochemical records of the subjects at first admission to the obesity outpatient clinic were examined. Results Eighty-three per cent (n = 1063) of the study population were women. Antithyroid peroxidase (anti-TPO) positivity was 14%, and antithyroglobulin (anti-TG) positivity was 15%. TSH was 1.8 mu IU/ml (1.3. 2.4) in antibody-negative subjects and 2.1 mu IU/ml (1.4. 2.9) in antibody-positive subjects. Neither TSH nor thyroid antibody positivity was associated with insulin resistance (IR) and atherogenic dyslipidaemia after adjustment for confounders. FT3 was positively associated with IR (P < 0.001) and atherogenic dyslipidaemia (P = 0.03); however, this association lost its significance after adjustment for age, gender and BMI. FT4 was negatively associated with IR and this association remained even after adjustment for confounders (P < 0.001). Conclusion TSH and thyroid antibody positivity were not related with metabolic measures. Low-normal FT4 had an inverse association with HOMA-IR even after adjustment for confounders.