Objective: Subclinical hypothyroidism (SCH) has been associated with increased carotid intima-media thickness (IMT) in recent studies, but this relationship is controversial. The aim of this study was to assess whether carotid IMT in patients with SCH differs from that in euthyroid subjects.
Methods: Prior to November 2011, we searched PUBMED, EMBASE, COCHRANE LIBRARY databases and the bibliographies of key articles to identify studies that reported carotid IMT in patients with SCH compared with euthyroid subjects. Two reviewers independently evaluated each potential study for eligibility, assessed the methodological quality, and extracted the data.
Results: We identified 8 observational studies with 3602 patients that met the eligibility criteria. In patients with SCH, the pooled estimate of the weighted mean difference (WMD) of increased carotid IMT was 0.056 mm (95% CI 0.020, 0.092; P = 0.002). Sensitivity analysis using a pooled sample of the 7 higher-quality studies demonstrated higher carotid IMT level in patients with SCH compared with those with euthyroidism (WMD, 0.064 mm, 95% CI 0.024, 0.105; P = 0.002). In a subgroup analysis, SCH was also associated with a significant increase in carotid IMT among patients with a mean TSH > 10.0 mIU/l (WMD, 0.082 mm, 95% CI 0.049, 0.116; P = 0.00). SCH was associated with a significant increase in systolic blood pressure (SBP), triglyceride (TG) levels, total cholesterol (TC) levels, low-density lipoprotein (LDL) levels and with a decrease in fasting plasma glucose (FPG).
Conclusion: This meta-analysis indicates that SCH is associated with an increased carotid IMT, which may due to elevated thyrotropin (TSH), dyslipidemia and hypertension. Increased IMT can also be present in patients with serum TSH values less than 10 mIU/l, although there is significant heterogeneity. Prospective studies with larger samples are necessary to evaluate these observations.
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