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09-03-2006 | Thyroid | Article

Thyroid disorders do not increase cardiac disease risk

Abstract

Free abstract

US researchers say that apart from a link between subclinical hyperthyroidism and atrial fibrillation (AF), thyroid function is not associated with cardiac disease or mortality.

Various lines of evidence have pointed to a link between thyroid hormone levels and cardiovascular disease, but the nature of the relationship remains unclear. To investigate further, Anne Cappola (University of Pennsylvania, Philadelphia) and team studied 3233 participants in the Cardiovascular Health Study, a large, prospective cohort study.

After excluding individuals with overt thyrotoxicosis or AF, 82% of the cohort had normal thyroid function, 15% had subclinical hypothyroidism, 1.6% overt hypothyroidism, and 1.5% overt hyperthyroidism. All diagnoses were made based on results from thyroid function tests.

During 13 years of follow-up, individuals with subclinical hyperthyroidism were more than twice as likely as euthyroid patients to develop incident AF (67 vs 31 events per 1000 person-years, p<0.001).

This effect persisted after adjustment for other risk factors for AF, Cappola et al reveal, giving an adjusted hazard ratio of 1.98.

However, there were no differences in the incidence of coronary heart disease, cerebrovascular disease, cardiovascular death, or all-cause death between euthyroid participants and those with any thyroid disease.

The researchers say their data do not support screening patients solely to prevent AF: around 2500 older individuals would have to be screened to find a single case of AF associated with subclinical hyperthyroidism, they estimate.

"Our findings suggest that if endogenous subclinical hyperthyroidism is detected, older individuals may benefit from treatment to prevent AF," the team concludes.

"Although our data are observational, they do not support treatment of individuals with subclinical hypothyroidism simply to prevent cardiovascular events."

This research was published in the Journal of the American Medical Association.