In a large study conducted in the UK, researchers found a strong connection between atrial fibrillation and very mild, subclinical hyperthyroidism. The results of the Birmingham Elderly Thyroid Study (BETS) were presented at the British Endocrine Societies April 2005 meeting. The study, which looked at nearly 6000 people over 65 who had no history of thyroid problems, measured thyroid function, finding that 2.2% had some evidence of a mildly overactive thyroid condition, even though they had no symptoms. This situation is known as subclinical hyperthyroidism. Among this group, more than one in ten had
an irregular heartbeat known as atrial fibrillation, which is a risk factor for stroke and heart disease. (The rate of atrial fibrillation among those with normal thyroid function is approximately one in twenty.)
The researchers did not go so far as to conclude yet that treating subclinical hyperthyroidism would prevent atrial fibrillation, but called for larger trials to explore whether this might be a benefit.
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