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

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.

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.

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).

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