At the start of the study, none of the participants had atrial fibrillation. Over an average of seven years of follow-up, more than 550 people developed the condition, the researchers noted.
Each year during the study, all the participants were given a 100-point memory and thinking test.
The researchers found that people with atrial fibrillation were more likely to have lower scores on the test at an earlier age, compared with those who didn't develop atrial fibrillation.
For example, the average score on the test decreased by about six points for people without atrial fibrillation between ages 80 and 85, compared to about 10 points for those with atrial fibrillation.
For those aged 75 and older with atrial fibrillation, the average decline was about three to four points faster every five years, compared to people without atrial fibrillation.
Scores below 78 points are associated with dementia, Thacker said.
The researchers predicted that on average, those without atrial fibrillation would score below 78 when they were 87, while people with atrial fibrillation would score below 78 when they were 85.
For more on atrial fibrillation, visit the American Heart Association.
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