The beneficial effect of L-thyroxine on lipid parameters in mild form of subclinical hypothyroidism

Abstract

Introduction: Overt hypothyroidism and severe subclinical hypothyroidism (ScH) are associated with dyslipidaemia, and its condition is reversible after thyroid replacement therapy. We investigated the effect of levothyroxine therapy on lipid parameters in patients with mild form of subclinical hypothyroidism (ScH).

Material and methods: Fifty-seven patients with newly diagnosed ScH with TSH levels below 10 mU/l and 30 age and sex-matched healthy subjects were included in the study. Lipid parameters were evaluated at the first visit in both groups, and after 6 months euthyroid stage in patients with ScH. Results: Average value of TSH in patients with ScH was 8.1 mU/l. At the baseline, ScH patients has a significantly higher total cholesterol and LDL-C levels, and lower HDL-C, than the control group (5.6±0.9 vs. 4.8±1.1, 3.4±1.0 vs. 2.9±0.8, and 1.5±0.5 vs. 1.7±0.9, mmol/L, P<0.05, respectively). Thyroid substitution therapy in ScH group, significantly decreased total cholesterol and LDL-C, and increased HDL-C (5.6±0.9 vs. 5.3±1.1, 3.4±1.0 vs. 3.2±1.1, 1.5±0.5 vs. 1.6±0.5, mmol/L, P<0.05 respectively). Also, TSH positively correlated with total cholesterol (r=0.147, P<0.05). Conclusion: Mild form of ScH is associated with hipercholesterolemia, which is reversible after levothyroxine treatment.