An irregular heartbeat may increase a person's risk of developing dementia, warns new research.
The study shows that people with a particular kind of irregular heartbeat called atrial fibrillation may experience a faster decline in thinking and memory skills, and have a greater risk of dementia than those without the condition.
With atrial fibrillation, a form of arrhythmia, the heart's normal rhythm is out of sync.
As a result, blood may pool in the heart, possibly forming clots that may go to the brain, causing a stroke.
The good news from the study is that people with atrial fibrillation who were taking anticoagulants, or blood thinners, to keep their blood from clotting were actually less likely to develop dementia than those who did not take blood thinners.
Study author Dr Chengxuan Qiu, of the Karolinska Institute and Stockholm University in Sweden, said: "Compromised blood flow caused by atrial fibrillation may affect the brain in a number of ways.
"We know as people age, the chance of developing atrial fibrillation increases, as does the chance of developing dementia.
"Our research showed a clear link between the two and found that taking blood thinners may actually decrease the risk of dementia."
For the study, researchers looked at figures from 2,685 participants with an average age of 73 who were followed as part of a larger study.
The participants were examined and interviewed at the start of the study, and then once after six years for those younger than 78 and once every three years for those 78 and older.
All the participants were free of dementia at the start of the study, but 243 people (nine per cent) had atrial fibrillation.
Through face-to-face interviews and medical examinations, the researchers gathered lifestyle and medical data at the start of the study and during each follow-up visit.
All were screened for atrial fibrillation, for overall thinking and memory skills, as well as dementia.
Over the course of the study, an additional 279 people (11 per cent) developed atrial fibrillation and 399 (15 per cent) developed dementia.
Researchers found that those who had atrial fibrillation had a faster rate of decline in thinking and memory skills than those without the condition and were 40 per cent more likely to develop dementia.
Of the 2,163 people who didn't have an irregular heartbeat, 278 people developed dementia (10 per cent). Of the 522 people with irregular heartbeat, 121 developed dementia (23 per cent).
Researchers also found that people who took blood thinners for atrial fibrillation had a 60 per cent decreased risk of dementia.
Of the 342 people who did not take blood thinners for the condition, 76 people developed dementia (22 per cent). Of the 128 people taking blood thinners, 14 developed dementia (11 per cent).
There was no decreased risk among people who took an antiplatelet treatment like aspirin.
Dr Qiu added: 'Assuming that there was a cause-and-effect relationship between using blood thinners and the reduced risk of dementia, we estimated that about 54 per cent of the dementia cases would have been hypothetically prevented if all of the people with atrial fibrillation had been taking blood thinners.
"Additional efforts should be made to increase the use of blood thinners among older people with atrial fibrillation."
The findings were published online by the journal Neurology.