Blood-thinning drugs not only reduce the risk of stroke in patients with atrial fibrillation but are also associated with a significant reduction in the risk of dementia among these patients, according to a new register-based study by researchers at Karolinska Institutet’s Department of Clinical Sciences, Danderyd Hospital.

The study was published in the European Heart Journal.

Atrial fibrillation (AF) is a common heart rhythm disorder that is known to be associated with an increased risk of stroke and dementia. Oral anticoagulants, or blood-thinning drugs, have been shown to reduce the likelihood of stroke but it has not been clear whether they could also prevent dementia in AF patients. However, it’s been hypothesised that they might protect against the small clots that can cause unnoticed microscopic strokes that eventually lead to cognitive deterioration.

Looking at data from Swedish registries, Mårten Rosenqvist and Leif Friberg at Karolinska Institutet’s Department of Clinical Sciences, Danderyd Hospital have examined the link between oral anticoagulant treatment and dementia in patients with AF. The researchers identified all patients in Sweden who had a diagnosis of AF between 2006 and 2014. Among 444,106 patients with atrial fibrillation, 26,210 were diagnosed with dementia during the study period.

The sooner treatment was started, the greater was the effect. Less than half of the patients were taking blood-thinning drugs to prevent blood clots when they first joined the study. Those who were taking blood-thinning drugs had a 29 per cent lower risk of developing dementia than patients who were not on such treatment at the start of the study. When the researchers looked at what happened during the period of time that the patients continued to take the drugs, they found a 48 per cent reduction in the risk of dementia. They also found that the protective effect was greater the sooner the treatment was started and that there was no difference between the older blood-thinning drug warfarin and the newer oral anticoagulants.

“Although we can’t prove a causal relationship, we believe that the results strongly suggest that blood-thinning drugs protect against dementia in AF patients,” said Professor Mårten Rosenqvist.

“Patients on oral anticoagulation for stroke prevention often stop taking the drugs after a few years. Doctors should explain to their patients how these drugs work and why they should use them. No brain can withstand a constant bombardment of microscopic clots in the long run,” said associate professor Leif Friberg.