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 μIU/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 μIU/ml (1·3-2·4) in antibody-negative subjects and 2·1 μIU/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.