The article discusses the associations between overt hypothyroidism (HT), ie, thyroid stimulating hormone (TSH) > 3.65 mIU/L and free thyroxine (fT4) < 9 pmol/L and subclinical HT (TSH >3.65, fT4 9–23 , in coronary heart disease, cholesterol, homocysteine and diabetes.
The association between overt hypothyroidism and coronary heart disease has been repeatedly observed (Becker 1985). Less evident is the role of asymptomatic mild elevation of thyroid stimulating hormone (subclinical hypothyroidism), notwithstanding that it represents the majority of patients with thyroid dysfunction. It was shown (Hak et al 2000) that even subclinical hypothyroidism independently doubled relative risk of myocardial infarction in females. The most frequent cause of hypothyroidism is the autoimmune thyroid disease (AITD) manifested by elevated thyroid antibodies, namely thyroid peroxydase antibodies (Samuels 1998). Thus, a sole increase in thyroid antibodies may potentially influence the coronary risk. The aim of our study was to establish the prevalence of thyroid dysfunction in a well defined sample of patients with manifest coronary heart disease and to assess its associations with other coronary risk factors.
In conclusion, thyroid dysfunction has to be considered a highly prevalent condition, mainly in females, which could potentially contribute to the overall coronary risk and may be amenable to secondary preventive intervention. The evidence of benefit of L-thyroxine substitution in addition to conventional therapies on morbidity and mortality of coronary patients remains to be elucidated by randomized pharmacological trials.