The effect of thyroxine replacement on reduction of small dense low-density lipoprotein (sdLDL) in patients with primary hypothyroidism.
J. Saito, T. Watanabe, Y. Matsuzawa, M. Omura & T. Nishikawa
Background: Dyslipidemia is a well-known manifestation of thyroid dysfunction and there is evidence of an association between hypothyroidism and coronary heart disease. Recently, small dense low-density lipoprotein (sdLDL) has been linked with development of cardiovascular disease. But relations between thyroid function and sdLDL remain incompletely understood.
Objective: Our objective was to determine whether replacement therapy with thyroxine for patients with hypothyroidism is associated with improvement of lipid profiles including sdLDL.
Design: We conducted a prospective clinical study. Nine patients with primary hypothyroidism were enrolled in this study and treated by replacement with thyroxine. Lipid profiles, sdLDL, TSH, thyroid hormone were measured in pre- and post-treatment blood samples.
Results: Seven patients (3 males and 4 females with Hashimotos disease) of the patients completed this study and mean duration of treatment that normalized TSH was 126 days (85153 days). The pre-/post-treatment TSH, free T4 (fT4), LDL cholesterol (LDL), sdLDL and sdLDL/LDL ratio were 181.0±219.2/7.3±7.5 μIU/ml, 0.4±0.2/1.3±0.3 ng/dl, 160.7±61.1/121.8±25.6 mg/dl, 26.1±16.8/14.7±4.7 mg/dl, 0.157±0.047/0.138±0.043, respectively. TSH and sdLDL were significantly decreased and fT4 was significantly increased after treatment.
Conclusion: The present study demonstrated a reduction of sdLDL levels of patients with hypothyroidism after treatment associated with an increase in thyroid hormone, which may contribute to some cardiovascular alterations. Even though we found a reduction in sdLDL levels after treatment, the mechanism of this effect was still not well understood.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.