Hypothyroid heart

Townsend Letter for Doctors and Patients, April, 2001 by Alan R. Gaby

Data on thyroid status, aortic atherosclerosis, and history of myocardial infarction were obtained at baseline in a random sample of 1,149 women (mean age, 69 years) participating in the Rotterdam Study (Rotterdam, The Netherlands). Subclinical hypothyroidism (defined as a TSH level greater than 4.0 mU/L, with a normal serum free thyroxine level) was present in 10.8% of participants and was associated with an increased age-adjusted prevalence of aortic atherosclerosis (odds ratio [OR] = 1.7; 95% CI, 1.1-2.6) and myocardial infarction (odds ratio = 2.3; 95% CI, 1.3-4.0). Additional adjustment for body mass index, total and HDL cholesterol level, blood pressure, and smoking status did not affect these estimates. The population attributable risk percentage for subclinical hypothyroidism associated with myocardial infarction was 14%; this percentage is within the range of that for known major risk factors (e.g., hypercholesterolemia, 18%; hypertension, 14%; smoking, 15%; diabetes, 14%).

Comment: The results of this epidemiological study suggest that subclinical hypothyroidism is a strong risk factor for atherosclerosis and myocardial infarction in elderly women. Moreover, although hypothyroidism is known to increase serum cholesterol levels, the association between thyroid function and cardiovascular disease found in this study was independent of cholesterol levels. Heart disease is a well-known complication of clinical hypothyroidism, and there is growing evidence that even subtle thyroid deficiency can promote the development of heart disease. Broda Barnes, M.D., (Hypothyroidism: the Unsuspected Illness, Harper and Row, 1976) reported that treatment with thyroid hormone was associated with a dramatic reduction in the incidence of coronary heart disease (CHD). Among 1,569 patients that he followed for 8,824 patient-years, only 4 new cases of CHD were observed, a 94% reduction in the expected incidence of the disease.

Hak AE, et at. Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study. Ann Intern Med 2000;132:270-278.