Subclinical hypothyroidism and vascular risk: an update

Abstract

Subclinical hypothyroidism (SCH), defined as elevated serum thyroid-stimulating hormone (TSH) in the presence of normal circulating free thyroxine (FT4) and triiodothyronine (T3), is a relatively common condition. Replacement treatment with levothyroxine is justified only for individuals with TSH levels >10 mIU/l. Serum lipid levels are influenced by thyroid status and there is evidence pointing to a link between SCH and an unfavorable lipid profile. Despite some conflicting data, most studies suggest that levothyroxine treatment may exert a beneficial effect on the lipid profile in SCH regarding mainly total cholesterol and low-density lipoprotein-cholesterol. Moreover, it appears that treatment may also improve some other markers associated with cardiovascular (CV) disease such as carotid intima media thickness (cIMT) indices of endothelial function and other predictors of vascular risk. The complex interaction between SCH and predictors of vascular disease may explain the variability of the results obtained from studies that assessed vascular events or even changes in some biochemical, functional or structural variables associated with an increased risk of vascular events. Further investigation is warranted by means of intervention studies to assess the clinical significance of levothyroxine treatment in SCH regarding CV risk.