Studies show the frequently prescribed medicines reduce the risk of being struck down by almost half.
The breakthrough has given fresh hope that a disease modifying therapy for the incurable condition is now in sight.
Tests showed blood thinning pills, known as anticoagulant drugs, reduced the risk of stroke in patients suffering irregular heartbeat.
But scientists also found they were associated with a “significant” reduction in dementia risk.
James Pickett, head of research at Alzheimer’s Society, said: “We know that what is good for your heart is good for your head. Because of this, many research studies are examining the benefits of treating problems with the blood and heart as a way to potentially prevent or slow down cognitive decline, including some funded by Alzheimer’s Society.”
Dementia news: Blood thinning drugs like warfarin ‘could protect against dementia’
The latest study, carried out by the Karolinska Institute in Stockholm, Sweden, was the largest ever to examine the link between anticoagulant treatment and dementia in patients with a common condition known as atrial fibrillation [AF].
Analysis of data on 444,106 AF patients between 2006 and 2014 found those taking drugs to prevent blood clots at the start of the study had a 29 per cent lower risk of developing dementia than those not on anticoagulant treatment. But crucially those who continued to take the drugs had a 48 per cent reduction dementia risk.
The study also found there was no difference in dementia prevention between the older blood-thinning drug warfarin and newer oral anticoagulants.
There are around 1.25 million people currently on oral anticoagulant drugs in the UK with warfarin being the most frequently prescribed.
Researchers said the results “strongly suggest” the drugs protect against dementia in AF patients.
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Atrial fibrillation is the most common heart rhythm disturbance, affecting around one million people in the UK. The condition becomes more common with age.
It is known to carry an increased risk of stroke but until now it was unclear whether anticoagulants could also prevent dementia. Scientists think that because the drugs can stop the big blood clots that cause stroke, they might also protect against the small clots that can cause unnoticed microscopic strokes that eventually lead to cognitive deterioration.
When they first joined the study 54 per cent of patients were not taking oral anticoagulants like as warfarin, apixaban, dabigatran, edoxaban or rivaroxaban.
The strongest predictors for dementia were lack of oral anticoagulant treatment, ageing, Parkinson’s disease and alcohol abuse.
Scientists also found the sooner oral anticoagulant treatment was started after a diagnosis of AF, the greater the protective effect against dementia.
The breakthrough has given fresh hope
Dr Leif Friberg, associate professor of cardiology at the Karolinska Institute, said: “As a clinician I know there are AF patients who have a fatalistic view upon stroke. Either it happens or it does not.
Few patients are fatalistic about dementia, which gradually makes you lose your mind. No brain can withstand a constant bombardment of microscopic clots in the long run.
“Patients probably want to hang on to as many of their little grey cells for as long as they can. In order to preserve what you’ve got, you should take care to use anticoagulants if you are diagnosed with AF, as they have been proved to protect against stroke and, which this study indicates, also appear to protect against dementia.”
Alzheimer’s, the most common form of dementia, is a disease known as the “long goodbye”. It usually starts with forgetfulness and can progress to complete loss of independence and in some cases people spend their last years bed bound and mute.
It affects 850,000 people in the UK, a figure expected to rise to one million by 2025. Research shows it doubles in prevalence every five years above the age of 65 but if onset could be delayed by five years, dementia prevalence would be halved.
There are around 1.25 million people currently on oral anticoagulant drugs in the UK
Dr Carol Routledge, director of research at Alzheimer’s Research UK, said: “Stroke is a major risk factor for vascular dementia. Not only do anticoagulants protect against stroke in people with an abnormal heart rhythm but this study also links them to a reduced risk of dementia.
“Dementia has a complex relationship with other health conditions and studies like this can help inform decisions around how those conditions are treated to bring most benefit to the individual. We desperately need to develop effective treatments that target the causes of dementia, and looking at the effects of existing drugs could radically accelerate the time it takes to find a life-changing treatment.”
The research was published in the European Heart Journal.
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: “Strokes caused by a clot blocking the blood vessels in the brain are a major cause of dementia, and atrial fibrillation is an important risk factor as it increases the chances of these clots forming. By treating AF patients with blood-thinning drugs, you reduce the risk of both stroke and dementia.
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“The number of people with dementia will rise substantially over the next two decades, which is why research into AF and stroke is so vital in helping to prevent the disease.”
Dr Shamim Quadir, Research Communications Manager at the Stroke Association, said: “This study hits home how vital it is for doctors to discuss the benefits of anticoagulant treatment with patients with AF, and why it’s important they keep taking their medication. AF increases a person’s risk of stroke by about five times, but anticoagulant drugs significantly reduce this risk.
“We also know that stroke and dementia are related, with stroke survivors at an increased risk of developing dementia too.
“Anybody with questions about their anticoagulant treatment, or risk of stroke should talk with their GP.”