Substantially elevated TSH, not traditional clinical subclinical thyroid disorder groupings, are associated with smaller LDL-P mean size: ELSA-Brasil

Abstract

LDL appears to drive atherogenesis in overt hypothyroidism, but in subclinical dysfunction, its role is not completely elucidated. The aim of this study was to evaluate subfractions of LDL in subclinical (SC) thyroid disorders. Individuals were divided into three groups by baseline thyroid function (SC hypothyroidism, euthyroidism, and SC hyperthyroidism). LDL particle (LDL-P) subfractions were analyzed by Nuclear Magnetic Resonance (NMR) spectroscopy. The association between LDL-P subfractions and thyroid groups and quintiles was evaluated by linear regression models. We evaluated 3304 participants (54.1% women, 51.2% white, mean age 50.6±8.7 years). In the univariate analysis, small LDL particle concentrations (SLDL-P) were not different between SC hypo- and hyperthyroidism compared to euthyroid individuals (p=0.485 and p=0.314, respectively). Large LDL-P (LDL-P) levels also did not differ in SC hyperthyroidism and SC hypothyroidism compared to euthyroidism (p=0.698 and 0.788 respectively). Intermediate LDL-P levels were not different across the groups. These numbers did not materially change in multivariate analysis. However, we also analyzed LDL subfractions according to quintiles of TSH. We showed that in the higher TSH quintile LDL subfractions presented a significantly smaller mean size of LDL subfractions compared to the first quintile. SC thyroid disorders are not associated with significant changes in LDL-P subfractions measured by NMR spectroscopy. However, it seems that the LDL mean size decreases as TSH levels increase, which may represent a more atherogenic lipid profile.