Subclinical hypothyroidism not a risk factor for heart disease

By medwireNews Reporters

Persistent subclinical hypothyroidism in older adults is not associated with an increased risk for cardiovascular (CV) events, US research shows.

In the analysis, researchers found no association between subclinical hypothyroidism and the 10-year risk for incident coronary heart disease (CHD), heart failure (HF), or CV death.

Additionally, there was no evidence of a gradient of risk or dose-response relationship by degree of thyroid-stimulating hormone (TSH) elevation, report Kristen Hyland (University of Pennsylvania, Philadelphia) and colleagues in the Journal of Clinical Endocrinology and Metabolism.

The study is the first cohort study to use repeated measures of thyroid functioning in examining CV risk, they note, and importantly, the findings do not support the treatment of subclinical hypothyroidism to prevent CV disease or HF.

The relationship between subclinical hypothyroidism and heart disease is controversial, with a recent meta-analysis suggesting the risk for CHD events is increased only in individuals with severe subclinical disease (TSH levels >10 mU/L). Similarly, three studies of HF risk in elderly patients found an increased risk only in those with TSH levels over 7 mU/L.

However, as the researchers in the current study point out, there is a concern that thyroid function test results change over time and the use of a single set of assays to define subclinical hypothyroidism might influence the relationship between CV events and subclinical disease.

For the current study, the researchers used data on 670 adults aged 65 years and older with subclinical atherosclerosis and 4184 euthyroid individuals from the Cardiovascular Health Study Hyland. They modeled subclinical hypothyroidism as a time-varying exposure using up to four serial thyroid function tests and found no association between persistent subclinical hypothyroidism and the incidence of CHD, HF, or CV death.

When subclinical hypothyroidism was stratified by degree of TSH elevation, again no significant association was observed in any of the TSH categories.

In an analysis that looked solely at patients with 2 years between thyroid function tests, the results were similar to the overall findings.

"Our data suggest that subclinical hypothyroidism, either transient or persistent, does not represent a risk factor for CHD, HF, or CV mortality in men and women aged 65 and older," conclude Hyland and colleagues.

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