[Effects of levothyroxine replacement on lipid profile in patients with mild subclinical hypothyroidism].

BACKGROUND AND OBJECTIVE: To evaluate the effects of levothyroxine (L-T4) replacement on lipoprotein profile in patients with mild subclinical hypothyroidism, defined as a serum TSH level between 5 to 10 mU/l with a normal serum free thyroxine level.

PATIENTS AND METHOD: We have prospectively studied 89 patients with mild subclinical hypothyroidism -10 male, 79 female; mean (standard deviation) TSH: 7.9 (1.3) mU/l-. The thyroperoxidasa antibodies were positive in 46 subjects and were treated with L-T4. The 43 patients with thyroperoxidasa antibodies negative were used as controls. In both groups fasting lipid profiles were measured at baseline and 40 weeks.

RESULTS: There were no significant differences in the age, serum concentrations of TSH, free thyroxine and lipid profile between 2 groups at baseline. After therapy, serum TSH levels had returned within the normal range in the L-T4 group and were now significantly lower than in the control group (p < 0.001). There were no significant differences in the changes from baseline to 40 weeks between patients in the L-T4 group and the control group for any of the lipid variables measured, expressed as the mean change in the L-T4 group minus the mean change in the control group and the 95% confidence interval (CI): total cholesterol, -0.27 mmol/l (95% CI, -0.69 to 0.16 mmol/l); LDLc, -0.27 mmol/l (95% CI -0.61 to 0.05 mmol/l).

CONCLUSIONS: Forty weeks L-T4 treatment does not significantly improve the lipid profile in patients with mild subclinical hypothyroidism.