Blood-thinning drugs may reduce dementia risk in people with irregular heartbeats

Wednesday October 25 2017

“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 such as 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 do not 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 to those not given the prescription. However, because of the type of study, the researchers cannot 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 prescribed to you.

However, you should not take anticoagulants if you are not at risk of blood clots, because the drugs 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 cannot prove cause and effect. The Sun’s headline described anticoagulant treatment as a “2p Alzheimer’s buster” which is unfortunate, as 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 to 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 was a retrospective cohort study, using 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 cannot prove that one thing (the drugs) causes another (the lower dementia risk). That’s because they cannot 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 to see who was prescribed anticoagulants within 30 days of diagnosis, and who was diagnosed with dementia during an average of around three years of follow-up. After adjusting for confounding factors, they calculated the risk of dementia for people with or without anticoagulant prescriptions.

The researchers also looked at the amount of time people in each group took anticoagulants. They found that in the anticoagulant group, people had access to the drugs during 72% of the study period. People in the no access group (i.e. they were not given an anticoagulant within a month of AF diagnosis) actually had access to anticoagulants for 25% of the study period. The researchers therefore reanalysed the data just looking at people who were consistently on anticoagulants compared to those who never took them.

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. They say this allowed them to make matched comparisons between the groups.

They also tested anticoagulant use with unconnected outcomes such as falls, flu, diabetes and chronic obstructive pulmonary disorders (COPD). They say that if anticoagulants were linked to any of them, then this would indicate there may be an underlying confounding factor they had not accounted for. This would mean they would not 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 had 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 such as warfarin with newer types such as dabigatran
  • 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 to 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.

Conclusion

If you’ve been diagnosed with AF and you have been prescribed anticoagulant treatments such as warfarin or dabigatran, we already know they protect you against having a stroke. This study suggests they may also help to protect you against dementia.

Cutting the risk of dementia for people who have a raised risk because of 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 other confounding factors not measured. This is the problem with retrospective observational studies - they cannot prove cause and effect.

Usually, we would want to see a randomised controlled trial (RCT) to follow this study, to find out if anticoagulant drugs really do have that effect. However, because people with AF are usually prescribed anticoagulants to reduce their risk of stroke, it would not be ethical to do an RCT, as it would leave people unprotected against stroke when a known preventive treatment is available.

Because of the difficulties of carrying out a proper trial, we will need to see more studies of the kind done here, in different populations, to see whether the results hold true. It would be useful in future studies to 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 one 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 are prescribed anticoagulants.

We also don’t know which types of dementia people were diagnosed with. AF may be more strongly linked to vascular dementia – caused by small blood clots blocking the blood vessels and starving the brain of oxygen – 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 in turn, can be triggered by smoking and obesity.

When it comes to dementia prevention, it is often the case that what is good for the heart is also good for the brain.

Analysis by Bazian
Edited by NHS Website