Subclinical Hypothyroidism and Cardiovascular Risk – An Overview of Current Understanding

Abstract

Subclinical or mild hypothyroidism is often associated with adverse cardiovascular risk factors, such as high cholesterol, together with hypertension, endothelial dysfunction and other atherosclerotic cardiovascular risk factors. The ischaemic abnormalities are probably related to long-term consequences of a slowly progressing development of hypothyroidism. In recent years, it has become evident that a consensus on the exact limits for cut-off between normal and subclinically hypothyroid individuals is not currently possible. The main reasons for this are differences for measurement of serum thyroid-stimulating hormone (TSH), that reference populations are very different and that a person’s intra-individual variability is much narrower than any population-based interval. Finally, the prevalence of subclinical hypothyroidism varies from 4 to 17% in different normal populations. Available evidence indicates that patients with subclinical hypothyroidism have developed or are at risk of developing an adverse cardiovascular profile and subclinical hypothyroidism is most likely a mild variant of overt hypothyroidism. There is currently no evidence for a treatment benefit, but studies to demonstrate the expected minor improvements have not been performed on a sufficiently large scale. Patients should be informed about the disease and based on a combined clinical and laboratory judgement, should be offered a therapeutic trial in case of even vague symptoms.