Subclinical hypothyroidism and the risk of hypercholesterolemia

BACKGROUND Subclinical hypothyroidism, defined as a mild elevation in thyroid-stimulating hormone (TSH) levels in patients with normal serum thyroxine levels, has been associated with elevationed levels in serum cholesterol in some sample populations. These studies, however, have included referred patients and large numbers of patients with previously treated hyperthyroidism. The aim of this study was to assess whether subclinical hypothyroidism is associated with abnormal lipid levels in a population-based sample. METHODS Data from adults older than 40 years who did not previously have a diagnosis of hypothyroidism or who were taking thyroid replacement medication were analyzed from the National Health and Nutritional Examination Survey (NHANES) III. Subclinical hypothyroidism was defined as a TSH value of 6.7 to 14.9 mU/L and normal thyroxine (n = 215). Euthyroid control adults included participants with a TSH in a normal range between 0.36 and 6.7 mU/L (n = 8,013). Outcomes examined were serum cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglyceride levels in those who had subclinical hypothyroidism and in euthyroid controls. RESULTS Persons meeting the criteria for subclinical hypothyroidism had higher mean cholesterol levels (226 vs 217 mg/dL, P =.003) and rates of elevated cholesterol levels (74.2% vs 63.9%, P = 0.02) than the euthyroid control group, but there were no significant differences in low-density lipoprotein (LDL) or high-density lipoprotein (HDL) levels. When adjusted for age, race, sex, and the use of lipid-lowering drugs, however, subclinical hypothyroidism was not related to elevations in cholesterol levels (adjusted odds ratio [OR] = 1.06, 95% confidence interval [CI], 0.57-1.97), LDL levels (adjusted OR = 0.89; 95% Cl, 0.59-1.35), or triglyceride levels (adjusted OR = 1.83; 95% Cl, 0.87-3.85) or to a low HDL level (adjusted OR = 0.94; 95% CI, 0.36-2.48). CONCLUSIONS Subclinical hypothyroidism does not appear to be associated with abnormalities in serum cholesterol or triglyceride levels when adjusted for confounding variables in this population-based study.