Low normal thyroid function as a determinant of increased large very low density lipoprotein particles

• TSH, free T4 and lipoprotein subfractions (NMR) were measured in euthyroid subjects.
• 61 Type 2 diabetic and 52 non-diabetic subjects were studied in the fasting state.
• Low-normal thyroid function was associated with large VLDL in all subjects combined.
• Low-normal thyroid function may adversely affect triglyceride metabolism.

ObjectivesLow-normal thyroid function may relate to increases in plasma cholesterol and triglycerides, but effects on lipoprotein subfractions are largely unknown. Associations of alterations in lipoprotein metabolism and functionality with low-normal thyroid function could be more pronounced in Type 2 diabetes mellitus (T2DM). We determined relationships of plasma lipids and lipoprotein subfractions with thyroid-stimulating hormone (TSH) and free thyroxine (free T4) in euthyroid subjects, and assessed whether such relationships are modified in the context of T2DM.Design and methodsTSH, free T4, (apo)lipoproteins and lipoprotein subfractions (nuclear magnetic resonance spectroscopy) were measured after an overnight fast in 61 T2DM subjects and 52 non-diabetic subjects.ResultsTSH and free T4 were similar in T2DM and non-diabetic subjects. Plasma triglycerides, large very low density (VLDL) particles, VLDL size and small low density lipoprotein (LDL) particles were increased, whereas high density lipoprotein (HDL) cholesterol was decreased in T2DM subjects (p ≤ 0.05 for each). Age-, sex-, and diabetes status-adjusted multivariable linear regression analysis demonstrated that plasma triglycerides were associated positively with TSH (β = 0.196, p = 0.039). Large VLDL particles (β = − 0.215, p = 0.020) and VLDL size were inversely associated with free T4 (β = − 0.285, p < 0.001). These relationships were not significantly modified by diabetes status (interaction terms: p > 0.10 for each). In all subjects combined, LDL and HDL subfraction characteristics were not significantly related to thyroid function status.ConclusionsLow-normal thyroid function may confer increased plasma triglycerides, large VLDL particles and increased VLDL particle size. These relationships are not to a major extent modified in the context of T2DM.