Subclinical Hypothyroidism and Cardiovascular Disease

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Subclinical Hypothyroidism and Cardiovascular Disease

Results from two studies suggest that treatment might be beneficial for older people with at least moderately elevated TSH levels.

Subclinical hypothyroidism — characterized by elevated thyroid-stimulating hormone (TSH) and normal free thyroxine (T₄) levels — reportedly affects about 4% of the general population and about 10% of people older than 70. Results from prior studies have conflicted on the clinical importance of subclinical hypothyroidism. Now, in two studies, researchers report on its cardiovascular effect.

A population-based cohort study from the U.S. involved 2730 healthy, community-dwelling elders (age range, 70–79); 12.4% had subclinical hypothyroidism (defined as TSH $≥$ 4.5 mIU/L). During 4 years of follow-up, a significant twofold increase in risk for congestive heart failure (CHF) occurred among subjects with subclinical hypothyroidism and TSH levels $≥$ 7 mIU/L, compared with euthyroid subjects. Subclinical hypothyroidism was not associated with risk for coronary heart disease or with mortality rates.

Of 2108 participants (mean age, 50) in a community-based study from Australia, 5.6% had subclinical hypothyroidism (defined as TSH $≥$ 4.0 mIU/L). During 20 years of follow-up, risk for CHD events was significantly higher among subjects with TSH levels >10 mIU/L than among euthyroid subjects (hazard ratio, 2.6); the increase in CHD risk among subjects with subclinical hypothyroidism and lower TSH levels was of borderline significance (HR, 1.6). Cardiovascular mortality was not increased in subjects with subclinical hypothyroidism.

Comment: In these studies, people with subclinical hypothyroidism and at least moderately elevated TSH levels — on a single baseline measurement — had elevated risks for subsequent heart disease. However, some of those who developed cardiac disease might have progressed to overt hypothyroidism (i.e., elevated TSH and low serum T₄) during follow-up. Although these results suggest that treatment might be beneficial for older people with subclinical hypothyroidism and TSH levels of at least 7 to 10 mIU/L, additional research is required to prove this point, as excessive levothyroxine therapy can have negative consequences.

— Jamaluddin Moloo, MD, MPH

Published in Journal Watch General Medicine January 3, 2006

Citation(s):

Rodondi N et al. Subclinical hypothyroidism and the risk of heart failure, other cardiovascular events, and death. Arch Intern Med 2005 Nov 28; 165:2460-6.