The new study was carried out by Leif Friberg and Mårten Rosenqvist, from the Karolinska Institute in Stockholm, Sweden. They started out from the already established link between atrial fibrillation and dementia.

A-fib is a common form of irregular heartbeat, or arrhythmia, and studies have shown that patients living with it have a considerably higher risk of developing dementia, including Alzheimer's disease.

Other studies have added that this association has nothing to do with the blood-thinning treatment that most A-fib patients are on.

But the precise role of anticoagulant, or blood-thinning, drugs on dementia risk is not yet known and has not been sufficiently investigated, explain the authors.

One theory suggests that, since anticoagulants prevent stroke by protecting against large blood clots, they should also prevent dementia by protecting against the small blood clots and microinfarctions that characterize it.

To explore this hypothesis, Friberg and Rosenqvist examined the incidence of dementia among patients with A-fib, comparing patients who took anticoagulants with those who did not.

The researchers also wanted to see whether or not the type of anticoagulant made any difference — such as whether newer blood thinners had a different effect on dementia risk when compared with old ones.