Relationship between Subclinical Thyroid Dysfunction and the Risk of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis of Prospective Cohort Studies

BACKGROUND Evidence on the association between subclinical thyroid dysfunction and the risk of cardiovascular outcomes are conflicting. METHODS AND RESULTS PubMed, EMbase, Web of Science, Cochrane Library, and China Biology Medicine (CBM) databases were searched from inception to July 10, 2016. A total of 16 studies were included for meta-analysis. We found that subclinical hypothyroidism was not correlated with coronary heart disease (CHD) (RR = 1.17; 95% CI, 0.91-1.52), total mortality (RR = 1.02; 95% CI, 0.93-1.13), cardiovascular mortality (RR = 1.06; 95% CI, 0.77-1.45), heart failure (RR = 1.17; 95% CI, 0.87-1.57), and atrial fibrillation (RR = 1.05; 95% CI, 0.91-1.21), except CHD mortality (RR = 1.37; 95% CI, 1.03-1.84). Subgroup analysis indicated a higher estimation risk in CHD (RR = 1.54; 95% CI, 1.00-2.39), cardiovascular mortality (RR = 2.14; 95% CI, 1.43-3.22), and CHD mortality (RR = 1.54; 95% CI, 1.11-2.15) among participants < 65 years. Furthermore, subclinical hyperthyroidism was found to be associated with CHD (RR = 1.20; 95% CI, 1.02-1.42), total mortality (RR = 1.27; 95% CI, 1.07-1.51), and CHD mortality (RR = 1.45; 95% CI, 1.12-1.86). CONCLUSIONS Subclinical hypothyroidism is likely associated with an increased risk of CHD mortality, and subclinical hyperthyroidism is likely associated with increased risk of CHD, CHD mortality, and total mortality.