Endocrine Abstracts

Introduction

The association between thyroid function within the normal range and body weight and related metabolic parameters has been the subject of numerous studies with inconsistent results not only in euthyroid healthy population but also in treated patients with autoimmune hypothyroidism.

Objective

To compare body mass index (BMI), blood glucose and serum lipids between women with autoimmune thyroiditis on levothyroxine replacement therapy and euthyroid healthy women.

Patients and methods

127 women with autoimmune thyroiditis receiving levothyroxine therapy (42.6 ± 1.9, 20–64 years) and 361 age-matched healthy women (40.6 ± 0.6, 19–65 years) were included in this retrospective study. All women were euthyroid with TSH and FT4 levels within reference range. TSH and FT4 levels were measured using ECLIA, fasting blood glucose, total cholesterol, HDL, triglycerides were measured and LDL was calculated using Friedewald’s formula. Women in the study did not have any significant comorbidities, diabetes mellitus, did not take metformin, lipid-lowering or estrogen-containing medications.

Results

Women on levothyroxine had higher levels of TSH (2.38 ± 0.09 vs 1.98 ± 0.05 mIU/l, P<0.01) and FT4 (11.50 ± 0.12 vs 10.89 ± 0.07 pmol/l, P<0.01) compared to healthy women. No significant differences between treated hypothyroid and healthy women were found in terms of BMI (26.7 ± 0.5 vs 27.3 ± 0.3 kg/m², P = 0.30), blood glucose (5.12 ± 0.05 vs 5.20 ± 0.03 mmol/l, P = 0.162), total cholesterol (5.21 ± 0.09 vs 5.27 ± 0.06 mmol/l, P = 0.638), HDL (1.43 ± 0.03 vs 1.43 ± 0.02 mmol/l, P = 0.483), LDL (3.27 ± 0.07 vs 3.32 ± 0.05 mmol/l, P = 0.681) and triglycerides (1.13 ± 0.06 vs 1.14 ± 0.03 mmol/l, P = 0.956) after adjustment for TSH and FT4. In women on levothyroxine TSH had positive correlation with HDL and FT4 was negatively associated with total cholesterol and LDL after adjustment for age and BMI. In healthy women TSH had positive association with total cholesterol and LDL and FT4 showed negative correlation with total cholesterol, HDL and triglycerides.

Conclusion

Women with autoimmune thyroiditis receiving levothyroxine have similar BMI, blood glucose and lipids compared with healthy euthyroid women provided that TSH is within reference range. Since there is no relationship between TSH and metabolic risk characteristics in euthyroid women on levothyroxine replacement therapy there would be no benefit in adjusting levothyroxine dose to achieve low-normal TSH.