Effect of l-thyroxine therapy on lipoprotein fractions in overt and subclinical hypothyroidism, with special reference to lipoprotein(a)

Abstract

The effect of l-thyroxine therapy on lipoprotein fractions was assessed in 15 patients with overt hypothyroidism (14 women and one man aged 45 ± 3.9 years; thyrotropin [TSH]: mean ± SEM, 42 ± 6.5 mIU/L; range, 20.5 to 106.5) and 14 patients with subclinical hypothyroidism (13 women and one man aged 41 ± 4 years; TSH: mean ± SEM, 9.1 ± 1 mIU/L; range, 5.1 to 17.3). Fasting serum lipid levels were measured initially and 4 months after achievement of a euthyroid state with incremental l-thyroxine therapy (TSH: mean ± SEM, 1.8 ± 0.4 mIU/L; range, 0.3 to 4.9 for both groups). In the ovartly hypothyroid group, restoration of a euthyroid state was associated with a significant reduction in total cholesterol, and apo B. In the subclinically hypothyroid group, there was a significant reduction of only total cholesterol (199.6 ± 13.2 v 183.4 ± 11.6 mg/dL) and LDL-C (131.6 ± 8.4 v 114 ± 9.25 mg/dL). In contrast, lipoprotein(s) [Lp(a)] was unaffected by the incremental adjustment of l-thyroxine therapy in both groups (overt, 34.3 ± 8.8 v 35.6 ± 6.7 mg/dL; subclinical, 23.0 ± 8.6 v 29.4 ± 9.5 mg/dL). We conclude that restoration of a euthyroid state in patients with overt hypothyroidism has no significant effect on Lp(a) levels, and confirm that subclinical hypothyroidism is associated with a significant increase in LDL-C, known to have an atherogenic effect.