“Common blood thinning drugs halve the risk of dementia for patients who have an irregular heartbeat,” reports the Mail Online.
Researchers in Sweden used the country’s health registry data to assess whether people with a condition called atrial fibrillation were less likely to get dementia if they took drugs like warfarin.
Atrial fibrillation (AF) is a heart condition that causes an irregular and often abnormally fast heartbeat. This can make the blood more likely to clot, which can lead to a stroke.
Most people with AF are prescribed anticoagulant drugs, which reduce the blood’s ability to clot.
Anticoagulants are often referred to as “blood-thinning drugs”, but this is technically incorrect as they don’t affect the density of blood.
People with AF are also at more risk of dementia, probably because of a build-up of tiny clots in the small blood vessels of the brain.
This study showed people with AF who were prescribed anticoagulants within a month of diagnosis had a 29% lower risk of getting dementia, compared with those not given the prescription.
But because of the type of study, the researchers can’t prove that anticoagulants are the reason for the reduced risk.
Still, as the researchers point out, the possible reduction in dementia risk is another reason to keep taking anticoagulant drugs if you’re prescribed them.
You shouldn’t take anticoagulants if you’re not at risk of blood clots as they can increase your risk of bleeding.
Where did the story come from?
The study was carried out by researchers at Danderyds University Hospital in Stockholm, Sweden.
It was published in the peer-reviewed European Heart Journal on an open access basis, making it free to read online.
Among the UK media, only the Sun pointed out that the study can’t prove cause and effect. The Sun’s headline described anticoagulant treatment as a “2p Alzheimer’s buster”, which is unfortunate – the type of dementia likely to be most affected by blood clots is not Alzheimer’s disease, but vascular dementia.
All the media used the more impressive 48% risk reduction figure from the study, which came from looking at people who took the drugs for most of the time, compared with people who never took them.
The more usual scientific standard is to use an intention to treat analysis of the figures, which gives a risk reduction of 29%.
Finally, The Guardian’s headline could have made it clearer that any reported dementia risk reduction only applied to people diagnosed with atrial fibrillation and not the population at large.
What kind of research was this?
This retrospective cohort study used data from Swedish health registries.
This type of study can help researchers spot patterns and links between factors (in this case anticoagulant drugs and dementia) but can’t prove that one thing (the drugs) causes another (the lower dementia risk).
That’s because researchers can’t rule out the effect of confounding factors that may influence the results.
What did the research involve?
Researchers looked at the records of all patients diagnosed with AF in Sweden from 2006 to 2014, excluding those who already had dementia.
They looked at who was prescribed anticoagulants within 30 days of diagnosis and who was diagnosed with dementia during an average of around 3 years of follow-up.
After adjusting for confounding factors, they calculated the risk of stroke for people with or without anticoagulant prescriptions.
The researchers used a statistical technique called propensity scoring to try to even out confounding factors of why some people did and others didn’t take anticoagulants despite all having a diagnosis of AF.
This is a suitable step to take, as compliance problems (not taking medication as instructed) are a known issue in some AF patients. They say this allowed them to make matched comparisons between the groups.
They also tested anticoagulant use with unconnected outcomes like falls, flu, diabetes and chronic obstructive pulmonary disorders (COPD).
They said that if anticoagulants were linked to any of them, this would indicate there may be an underlying confounding factor they hadn’t accounted for.
This would mean they wouldn’t be confident making any association between anticoagulants and dementia risk.
What were the basic results?
The researchers found:
- 26,210 of the 444,106 people in the study group got dementia – a rate of 1.73 dementia cases per 100 people each year
- people who’d started anticoagulants shortly after AF diagnosis were 29% less likely to get dementia (hazard ratio [HR] 0.71, 95% confidence interval [CI] 0.69 to 0.74)
- there was no difference between rates of dementia when directly comparing older anticoagulants like warfarin with newer types, such as clopidogrel
- people who had anticoagulant prescriptions 80% of the time were 48% less likely to get dementia than people who never had anticoagulant prescriptions (HR 0.52, 95% CI 0.5 to 0.55)
- there was no association between anticoagulants and falls or flu
Anticoagulant use slightly increased the risk of diabetes and COPD, but as this association was in the opposite direction from that for dementia, the researchers remained confident in their results.
They also found that people prescribed anticoagulants were likely to be younger and healthier.
Apart from not taking anticoagulants, the factors most closely linked to chances of getting dementia were older age, Parkinson’s disease and alcohol abuse.
How did the researchers interpret the results?
The researchers said their results “strongly suggest that oral anticoagulation treatment protects against dementia in atrial fibrillation” and that “early initiation of anticoagulant treatment in patients with AF could be of value” to prevent dementia.
If you’ve been diagnosed with AF and prescribed anticoagulant treatments such as warfarin or clopidogrel, we already know they protect you against having a stroke. This study suggests they may also help protect you against dementia.
Cutting the risk of dementia for people who have a raised risk from AF would be an exciting step forward.
Unfortunately, we can’t tell from this study whether the protection against dementia was down to the anticoagulants because of the possible effect of unmeasured confounding factors.
Usually, we’d want to see a randomised controlled trial (RCT) to follow this study to find out if anticoagulant drugs really do have that effect.
But because people with AF are usually prescribed anticoagulants to reduce their risk of stroke, it wouldn’t be ethical to do an RCT, as it would leave people unprotected against stroke when a known preventative treatment is available.
Because of the difficulties of carrying out a proper trial, we’ll need to see more studies of the kind done here, in different populations, to see whether the results hold true.
It would be useful if future studies have clearer information about which confounding factors are being taken into account.
There are a few things we don’t know from this study.
- The researchers were unable to differentiate between types of AF. Some people have just 1 episode of AF that doesn’t return or goes away with treatment, while others have persistent AF that happens all the time. The type of AF may affect both dementia risk and whether you’re prescribed anticoagulants.
- We also don’t know which types of dementia people were diagnosed with. AF may be more strongly linked to vascular dementia than Alzheimer’s disease. But we don’t know for sure which type of dementia might be helped by taking anticoagulants.
You can reduce your risk of vascular dementia by avoiding conditions such as type 2 diabetes and high blood pressure, which can be triggered by smoking and obesity.
When it comes to dementia prevention, it’s often the case that what’s good for the heart is also good for the brain.
Published by the NHS on 25/10/17