Objective: Although lipid abnormalities are well described in hypothyroidism, effects on apolipoproteins are less well understood. The aim of this study was to examine the effects of thyroid dysfunction on plasma lipids and apolipoproteins.
Design: A prospective study of lipids and apolipoproteins before and after treatment of hypothyroidism and hyperthyroidism.
Patients: Eighteen patients with hypothyroidism and 5 patients with hyperthyroidism were included.
Measurements: Plasma cholesterol, triglycerides, HDL cholesterol, apo AI, apo AII, and apo E were measured before and after treatment of the thyroid abnormality.
Results: Total and HDL cholesterol, apo AI and apo E decreased with treatment of hypothyroidism, while triglycerides and apo AII levels were unchanged. The total/HDL cholesterol and LDL/HDL cholesterol ratios also decreased with treatment of hypothyroidism. In contrast, treatment of hyperthyroidism was associated with an increase in total and HDL cholesterol, and apo AI. Triglycerides, apo AII and Apo E were unchanged by treatment of hyperthyroidism. The total/HDL cholesterol and the LDL/HDL cholesterol ratios increased with treatment of hyperthyroidism.
Conclusions: Hypothyroidism and hyperthyroidism have opposite effects on plasma lipids and apolipoproteins. In hypothyroidism, total and HDL cholesterol, total/HDL cholesterol ratio, apo AI and apo E are elevated. The increase in apo AI without a concomitant increase in apo AII suggests selective elevation of HDL2. In contrast, hyperthyroidism is associated with decreased total and HDL cholesterol, total/HDL cholesterol ratio, and apo AI levels. These effects are reversible with treatment of the underlying thyroid disorder.