Subclinical hypothyroidism and the risk for cardiovascular diseases. Are epidemiological studies giving the right answers?

Abstract

There is ongoing debate whether subclinical hypothyroidism may exert deleterious effects on the cardiovascular system with the consequences of increased morbidity and mortality. To elucidate this problem many epidemiological studies have been performed, however, these studies have not given an unambiguous answer so far. Many confounding elements are influencing the evaluation of these investigations which must be taken into consideration. Authors argue for the use of age specific reference limits for TSH (especially in older age, where TSH level is often shifted to a higher level) to avoid significant misclassification of patients with abnormal TSH who may or may not have thyroid dysfunction. Furthermore, recent studies have shown that subclinical hypothyroidism is associated with increased ischemic heart disease risk, mainly in individuals under the age of 65 years. In the future, well designed prospective randomized studies with age stratified groups and vascular events as the primary endpoint are required and it is anticipated that these studies will give the proper answer whether early substitution therapy with thyroxin will be able to reverse the ischemic heart disease risk in affected patients.