Subclinical hyperthyroidism and the risk of cardiovascular events and all-cause mortality: an updated meta-analysis of cohort studies.

OBJECTIVES Whether subclinical hyperthyroidism (SCH) results in poor prognosis remains controversial. Our aim was to evaluate the association between SCH and the risk of cardiovascular disease (CVD), cardiovascular mortality, and all-cause mortality by conducting a meta-analysis of cohort studies. METHODS The PubMed and Embase databases were searched through November 2011 to identify studies that met pre-stated inclusion criteria. Relevant information for analysis was extracted. Either a fixed or a random effects model was used to calculate the overall combined risk estimates. RESULTS Seventeen cohort studies were included in this meta-analysis. The overall combined relative risks for individuals with SCH compared with the reference group were 1.19 (95% confidence interval (CI): 1.10 to 1.28) for CVD, 1.52 (95% CI: 1.08 to 2.13) for cardiovascular mortality, and 1.25 (95% CI: 1.00 to 1.55) for all-cause mortality. Subgroup analysis by sample source (community or convenience sample) showed that the significant association for cardiovascular and all-cause mortality only existed when pooling studies from convenience samples. Heterogeneity was observed when pooling studies on the association between SCH and cardiovascular and all-cause mortality. Sensitivity analysis showed omission of each individual study did not significantly change the pooled effects. No evidence of publication bias was observed. CONCLUSIONS Our findings demonstrated that SCH significantly increased the risk of CVD for the general population and the risk of cardiovascular and all-cause mortality for the individuals with other morbidities.