HealthDay News — Higher levels of free thyroxine (FT4) may indicate a greater risk of sudden cardiac death, even if those levels aren’t abnormally high, according to a study published in the issue of Circulation.

Layal Chaker, MD, a research fellow in endocrinology and epidemiology at the Erasmus University Medical Center Rotterdam in the Netherlands, and colleagues analyzed 10,318 patients in the Rotterdam Study, a long-term investigation of chronic disease among the middle-aged and elderly in the Netherlands. The researchers compared thyroid-stimulating hormone and FT4 levels from blood samples against the number of sudden cardiac deaths that occurred in these patients.

The researchers found that higher levels of FT4 were associated with an increased SCD risk, even in the normal range of thyroid function (hazard ratio, 2.28 per 1 ng/dL FT4). In addition, the 10-year risk of sudden cardiac death increased in euthyroid participants from 1 to 4 percent with increasing FT4 levels.

Chaker had expected thyroid hormone levels to increase risk of sudden cardiac death, but to do so by affecting cardiovascular risk factors such as cholesterol levels and blood pressure. “We were surprised to see that when we control our analyses for these factors, the association remained similar, suggesting that other pathways could play a role,” Chaker told HealthDay.

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