Association between Subclinical Thyroid Dysfunction and Coronary Heart Disease and Cardiovascular Mortality: A Systematic Review

The association between subclinical thyroid dysfunction and coronary heart disease and cardiovascular mortality is controversial. In this cohort studiy we reviewed the association between subclinical thyroid dysfunction and coronary heart disease and cardiovascular mortality. Electronic search was done in medline and PubMed from 1950 to 2010 and fourteen related studies were found. Because of the heterogenicity between studies for defenitions and adjusted variables, those with larger sample size (more than 2000) were included for final analysis. Eight cohort studies met criteria for selection, but the results differed. In one study with the largest sample size the risk of cardiovascular mortality was increased in women for every one unit increase in serum TSH. In another study with a similar follow up duration of about 20 years, coronary heart disease events and cardiovascular mortality were increased in groups with subclinical hypothyroidism. In one study with moderate follow up of 12.5 years, the risks of cardiovascular mortality and coronary heart disease events were not increased in the group with subclinical thyroid dysfunction, compared to the euthyroid group. We found no definite conclusion based on the studied papers. However, it seems that subclinical thyroid dysfunction may cause an increased risk of coronary heart disease and cardiovascular mortality. We propose that larger cohort studies with appropropriate design for decreasing heterogenicity should be implemented, using dynamic thyroid function.