Higher free thyroxine levels within the normal range increased the risk for atrial fibrillation, especially among younger adults, according to recent study findings published in The Journal of Clinical Endocrinology & Metabolism.
“The prevalence of [atrial fibrillation] and its burden on health care is increasing despite efforts to control risk factors,” the researchers wrote. “Acknowledging nonclassical risk factors might aid in the recognition and decision making concerning [atrial fibrillation].”
, MD, PhD, of Erasmus University Medical Center in the Netherlands, and colleagues evaluated data from the Rotterdam Study on 9,166 adults aged 45 years and older with thyroid-stimulating hormone and/or free thyroxine measurements and an atrial fibrillation (AF) assessment to determine the relationship between normal thyroid function and AF. Follow-up was conducted for a median of 6.8 years. Overall, there were 399 prevalent and 403 incident AF cases.
Higher risks for AF were found with higher free thyroxine levels (HR = 1.63; 95% CI, 1.19-2.22) after comparing those in the higher quartile with those in the lowest quartile (P for trend = .005).
Among participants aged 65 years or older, the 10-year absolute risk increased from 6% to 12% compared with an increase from 1% to nearly 9% among younger participants.
AF was not associated with TSH levels.
“There is an increased risk of AF with higher [free thyroxine] levels in the normal range of thyroid function,” the researchers wrote. “This suggests caution in decision making regarding intensity of treatment and subclinical hypothyroidism. Assessing thyroid function, even in the normal range, for risk prediction of AF development should be further investigated.” – by Amber Cox
The researchers report no relevant financial disclosures.