Exploring the Effect of Thyroid Hormone on Serum Lipoprotein (a) Levels in Patients With Thyroid Hormone Dysfunction: A Systematic Review

Genetic variations among people mainly determine the blood levels of lipoprotein (a) (Lp(a)), and it is relatively stable throughout one's lifetime. Nevertheless, there could still be other factors that control the Lp(a) level. Thyroid hormones are known to influence the serum lipid level by regulating the expression of key enzymes that are involved in lipid metabolism. Both hypo and hyperthyroidism are associated with changes in lipid levels. Even though thyroid hormone abnormalities have been shown to alter traditional lipid parameters like low-density lipoprotein (LDL-C), its influence on Lp(a) has not been established. This review aims to identify the relationship between Lp(a) and thyroid hormones by reviewing data from correlative studies and observing treatment-related Lp(a) level changes in thyroid disorders from interventional studies. We searched MEDLINE, Cochrane, and Google Scholar databases with predefined search criteria and search strategies for paper identification. Individual reviewers reviewed identified papers for selection. Finalized papers were reviewed for Lp(a) levels and their responses to treatment in patients with thyroid disorders to establish the relationship between Lp(a) and thyroid hormone. We concluded that the data were limited and sometimes contradicted one another to establish a clear relationship between Lp(a) and thyroid hormones. Even though correlative studies data showed strong indications that overt-hypothyroidism was associated with high Lp(a) levels, thyroid hormone replacement studies did not show any significant changes in Lp(a) levels compared to pre-treatment in patients with both overt-hypothyroidism and subclinical hypothyroidism. More clinical trials focusing on Lp(a) with longer periods of treatment and follow-up in thyroid patients are needed to establish the relationship between the two. The possibility of dose-related Lp(a) responses to thyroid hormone treatment should also be explored.