Endothelial Function in Patients with Subclinical Hypothyroidism: A Meta-Analysis

Area of Science:

• Endocrinology
• Cardiovascular Medicine
• Vascular Biology

Background:

• Subclinical hypothyroidism (SCH) is a condition characterized by elevated thyroid-stimulating hormone (TSH) levels with normal free thyroxine (T4) and triiodothyronine (T3).
• Endothelial dysfunction is an early marker of atherosclerosis and cardiovascular disease.
• The relationship between SCH and endothelial function requires further clarification.

Purpose of the Study:

• To systematically evaluate the association between subclinical hypothyroidism (SCH) and endothelial dysfunction.
• To assess endothelial function using carotid intima-media thickness (C-IMT) and brachial artery flow-mediated dilation (FMD).

Main Methods:

• A comprehensive meta-analysis of studies comparing C-IMT and FMD in SCH patients versus euthyroid subjects.
• Searches were conducted in PubMed, Embase, and Cochrane Library databases up to July 2017.
• Random-effects models were used to calculate pooled estimates, with heterogeneity assessed by I² statistics and publication bias by funnel plots and Egger's test.

Main Results:

• The meta-analysis included 10 studies (760 subjects) for FMD and 23 studies (1521 subjects) for C-IMT.
• SCH was significantly associated with increased C-IMT (WMD 0.069 mm; p<0.001) and decreased FMD (WMD -1.848%; p<0.001).
• SCH was also linked to higher diastolic blood pressure, systolic blood pressure, triglycerides, total cholesterol, and LDL-C levels.

Conclusions:

• Subclinical hypothyroidism is associated with endothelial dysfunction, indicated by increased C-IMT and reduced FMD.
• Elevated TSH levels may contribute to endothelial dysfunction in SCH.
• Hypertension and dyslipidemia are likely key factors in the development of endothelial dysfunction in SCH patients.