LDL/HDL-changes in subclinical hypothyroidism: possible risk factors for coronary heart disease

The aim of the present study was to evaluate the lipid profiles (total cholesterol, triglycerides, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, and the electrophoretic low-density lipoproteins and high-density lipoproteins) in patients with subclinical (n = 52) and overt hypothyroidism (n = 18) in comparison to normal controls (28 and 18, respectively), matched for age, sex and body mass index. Subclinical hypothyroidism was defined as a syndrome with normal free thyroxine and total thyroxine but elevated basal thyrotrophin levels and/or an exaggerated TSH response to oral thyrotrophin releasing hormone. In subclinical hypothyroidism there was an elevated LDL concentration (P less than 0.01), a diminished HDL fraction (P less than 0.05) and a borderline elevated LDL-C (not reaching the limit of significance, P = 0.07). Total cholesterol and triglyceride concentrations remained unaltered. For the whole group of patients and controls significant negative correlations were found between LDL-C and T4 (P less than 0.04), total cholesterol and free thyroxine-index (P less than 0.01); positive correlations could be demonstrated between LDL-C and basal TSH (P less than 0.03), the ratio total cholesterol/HDL-C and basal TSH (P less than 0.03), and triglycerides and basal TSH (P less than 0.01). Our data provide a possible explanation for the higher prevalence of coronary heart disease reported in subclinical hypothyroidism. There may well be a case for the detection and early treatment of such individuals.