Effect of L-thyroxine versus placebo treatment on serum lipid levels in subclinical hypothyroidism

Abstract

Objective Subclinical hypothyroidism is a common disease. However, whether L-thyroxine replacement treatment can affect serum lipids in cases of subclinical hypothyroidism remains controversial. The objective of this meta-analysis was to assess the effect of L-thyroxine therapy on serum lipid levels of patients with subclinical hypothyroidism. Methods Literature dated until July 2015 was retrieved from the Cochrane Library, PubMed, Medline, Google Scholar, and Embase searching for the keywords hyroxine, levothyroxin and levothyroxine. All randomized controlled trials (RCTs) to determine the effects of L-thyroxine replacement on serum lipid levels were included in this study. After screening, the eligible RCTs were included in this meta-analysis. Statistical analyses were performed by the Review Manager 5.2 software. All the assessed outcomes were continuous data. Results A total of 7 RCTs involving 319 patients were included. The overall methodological quality of the RCTs was good. Results showed that the serum low density lipoprotein-cholesterol (LDL-C) level significantly decreased after L-thyroxine treatment [mean difference (MD) : -0.23; 95% CI: [-0.44, -0.03]; P=0.02]. Meanwhile, changes in the total cholesterol (MD: -0.18; 95% CI: [-0.40, 0.03]; P=0.09) , triglyceride (MD: -0.02; 95% CI: [-0.17, 0.13]; P=0.78) , and high density lipoprotein-cholesterol (MD: -0.06; 95% CI: [-0.14, 0.02]; P=0.14) levels were not significant. Conclusions All available RCT evidence on the effect of L-thyroxine on serum lipid levels in subclinical hypothyroidism revealed a significant improvement in the serum LDL-C levels. However, the serum TC, TG, and HDL-C levels did not significantly change. Key words: Thyroid hormones; Randomized controlled trials; Meta-analysis; Subclinical hypothyroidism; Serum lipids