Association between subclinical hypothyroidism and blood pressure--a meta-analysis of observational studies

This meta-analysis aimed to examine the relationship between subclinical hypothyroidism (SCH) and blood pressure (BP).

A systematic search of MEDLINE and EMBASE databases was performed to identify all related cross-sectional studies and baseline data in prospective cohort studies in the general population. Weighted mean differences (WMDs) of systolic blood pressure (SBP) and diastolic blood pressure (DBP) between SCH and euthyroid groups were calculated. Subgroup analyses and meta-regression were used to explore potential heterogeneities among studies.

Twenty studies with 50,147 individuals were included. The WMDs of SBP and DBP were 1.47 mm Hg (95% confidence interval [CI] 0.54-2.39 mm Hg, P = .002) and 0.44 mm Hg [95% CI: -0.15-1.02 mm Hg, P = .142] between SCH and euthyroid groups, respectively. Significant heterogeneity was indentified among the included studies. Subgroup analysis showed that differences in study design, gender, and thyroid-stimulating hormone (TSH) cutoff level were not associated with the WMD of SBP, except for age difference between SCH and euthyroid groups. Meta-regression revealed a significant association between WMDs of SBP and age difference between the 2 groups (P = .015).

In this meta-analysis, SCH was associated with slightly higher SBP, which could be attributed to the age difference between SCH and euthyroid groups in the general population. However, this study could not exclude an association between SCH and BP. Prospective studies are needed to confirm these findings.