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.