People living with Alzheimer's disease and atrial fibrillation may experience a slower decline in thinking and memory when treated with newer blood-thinning medicines, says a new Swedish study. Researchers found that patients taking newer oral anticoagulants, known as non-vitamin K oral anticoagulants (NOACs), had a slower decline in cognitive function than those taking the older blood thinner warfarin or those who were not taking anticoagulants. The study was published in the European Heart Journal.

The findings are important because atrial fibrillation, an irregular heart rhythm, is common among older adults and can increase the risk of blood clots and stroke. Doctors prescribe blood thinners to reduce this risk. Researchers say there are reasons to believe that preventing small blood-vessel blockages and other damage to the brain could also help preserve cognitive function. However, the study does not prove that NOACs directly slow Alzheimer's disease.

Maria Eriksdotter, professor at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, and senior consultant in geriatric medicine at Karolinska University Hospital, who led the study, said, "There are reasons to believe that the treatment could have a positive effect on cognition, for example by improving blood flow and reducing small-scale damage in the brain."

What Did The Study Find?

Researchers from Karolinska Institutet analysed data from Sweden's national register for cognitive disorders and dementia. The study included 7,308 people who had both Alzheimer's disease and pre-existing atrial fibrillation.

The participants were divided into three matched groups based on their anticoagulant treatment. There were 1,690 people taking NOACs, 2,277 taking warfarin and 3,341 who were not taking an anticoagulant.

The researchers followed changes in cognitive function using the Mini-Mental State Examination, or MMSE. This is a commonly used test that assesses areas such as memory, orientation, attention and other thinking abilities.

The results showed that people taking NOACs experienced a slower decline in MMSE scores than both those taking warfarin and those not receiving anticoagulant treatment. The difference was about 0.2 points per year. Researchers described the change as modest for an individual year, but said that even a small difference could become more meaningful if it continues over several years.

Nanbo Zhu, researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, said, "The difference is modest for an individual patient from one year to the next, but over a longer period even such an effect could influence how cognitive function develops. Our findings suggest that NOAC treatment may also be significant for cognition in this patient group."

What Are NOACs?

NOACs are a newer group of oral blood thinners used mainly to prevent blood clots and strokes in people with atrial fibrillation. Unlike warfarin, they do not work by blocking vitamin K.

Atrial fibrillation can cause blood to pool in the heart, increasing the chance of clot formation. If a clot travels to the brain, it can cause an ischaemic stroke. Repeated small disruptions to blood flow may also contribute to brain damage and cognitive problems.

The researchers suggest that preventing these could be one possible explanation for the link between NOAC treatment and slower cognitive decline. However, this is one possible biological explanation and was not directly established by the study.

NOACs Were Also Linked To Lower Stroke Risk

The study looked at several health outcomes in addition to cognition. Compared to people who were not taking anticoagulants, NOAC users had lower rates of death, ischaemic stroke or systemic embolism, and fractures. Warfarin users also had lower rates of death and ischaemic stroke or systemic embolism compared with people who were not taking anticoagulants. However, warfarin was linked to a higher rate of major bleeding.

When NOACs were compared directly with warfarin, NOAC use was associated with a lower rate of ischaemic stroke or systemic embolism and a lower rate of major bleeding.

Why Could Blood Thinners Affect The Brain?

One possible explanation is that atrial fibrillation can affect the brain even when a person has not experienced a stroke. Small blood clots or disruptions in blood flow may cause tiny areas of damage that are difficult to detect but could contribute to cognitive decline over time.

By reducing the formation of blood clots, anticoagulants may help lower the risk of these vascular events. Researchers also suggest that better preservation of blood flow could potentially have a positive effect on brain health.

However, Alzheimer's disease is a complex condition involving several biological processes. Blood clot prevention does not address all of the mechanisms involved in the disease, so the findings should not be interpreted as treatment that NOACs are an Alzheimer's treatment.

The study has important limitations. Since it was an observational study, researchers cannot say that NOACs themselves caused the slower cognitive decline. Other differences between patients could have influenced the results.

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