The butterfly-shaped thyroid gland located around your windpipe in the neck may seem small, but has widely varying and far-reaching functions. Its chief hormone, thyroxine, regulates various metabolic processes in your body. It regulates them throughout our life. When thyroid levels are deranged, they can have different adverse effects. Both high and low levels of thyroxine have shown links to several heart diseases, including atrial fibrillation, and heart failure. Now, a previously unknown link has been found between mildly elevated thyroid levels and sudden cardiac death.

What is sudden cardiac death?

Sudden cardiac death (SCD) describes an unexpected death in a short time. Usually within 1 hour since the first symptom can appear among anyone with known or unknown heart problems. It can present with non-specific complaints, like:

  • Chest pain
  • Fatigue
  • Palpitations

Those at high risk for sudden cardiac death include those who lead a sedentary lifestyle, suffer from hypertension, diabetes, high cholesterol levels, smoke, or have a family history of coronary artery disease and SCD. Now, a large population-based study has uncovered a new risk factor – high thyroxine levels.

Salient features of the study

Published in the journal Circulation recently, the study followed roughly 10,000 participants of 45 years of age or older, with 261 incidents of SCDs. The study, conducted by Layal Chaker MD and colleagues at Erasmus University Medical Center Rotterdam in the Netherlands, focused on the association of Thyroid Stimulating Hormone (TSH) and a fraction of thyroid hormone called Free Thyroxine (FT4). Adjustments were done for other cardiovascular risk factors including hypertension, smoking and cholesterol levels. The researchers found that high levels of FT4, even within the normal range, was associated with increased risk of SCDs. Surprisingly, the 10-year-risk of SCDs also rose from 1 to 4% in people with overall normal thyroid levels, who had increasing levels of FT4. The mechanism for this is yet to be understood, but the finding suggests a revision to the approach to correcting low and high thyroid levels.

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