Are serum TSH levels associated with oxidized low-density lipoprotein? Results from the Study of Health in Pomerania.

OBJECTIVE: Oxidized LDL (oxLDL) is involved in the pathogenesis of atherosclerosis. Thus, it is important to investigate putative risk factors for increased oxLDL. Evidence suggests that, compared to euthyroid individuals, LDL-cholesterol (LDL-C) levels are lower in individuals with overt hyperthyroidism. Whereas oxidization of LDL-C into oxLDL is increased in overt hyper- and hypothyroidism, it has not been investigated whether subclinical thyroid dysfunction impacts on oxLDL levels in general. We have analysed the association between serum thyrotrophin (TSH) levels and oxLDL in a population-based study. DESIGN, PATIENTS AND MEASUREMENTS: Of the 4308 individuals enrolled in the Study of Health in Pomerania, data from 3519 individuals were analysed (680 missing the oxLDL variable). oxLDL was measured by the oxLDL competitive ELISA on a BEP 2000. Multivariable linear regression models were performed to assess the association between serum TSH and oxLDL levels. RESULTS: TSH was positively associated with oxLDL in a curvilinear fashion with increasing serum TSH levels. Subgroup analyses revealed a significant association only in the group of individuals >60 years. Additionally, serum TSH levels were not associated with the ratio of oxLDL to LDL (ß = -0·04; 95% CI = -0·08, 0·01; P = 0·084). CONCLUSIONS: We demonstrate an association between serum TSH and oxLDL levels especially in the range of subclinical thyroid disease. Our study suggests that serum TSH levels affect LDL-C production or clearance rather than the LDL-C oxidation processes.