Behind the headlines: can one in three dementia cases be prevented?


By Kirsty Marais | Thursday 20 July 2017

‘How can I prevent dementia?’ is one of the most common questions we hear at Alzheimer’s Research UK. And no wonder: without treatments to affect the underlying diseases, it’s natural for people to look for ways to stave off the condition. It’s also hugely important for government, as action to help people reduce their dementia risk should mean fewer people developing the condition in future. So today’s headlines, suggesting that a third of dementia cases could be preventable, will doubtless be good news for many.

Understanding dementia risk is a complex task, and the researchers behind this report, which was presented today at the Alzheimer’s Association International Conference in London, had a big challenge on their hands. Let’s take a look at what they did.

Calculating risk

The headlines are based on a report from the Lancet Commission – a comprehensive piece of work part-funded by Alzheimer’s Research UK, which pulled together existing evidence on dementia prevention, diagnosis, treatment and care. The report summarises evidence from existing studies, and calculates how individual risk factors might affect the overall number of people living with dementia.

This is tricky task. Most of the evidence on dementia risk comes from observational studies: these look to see whether people with particular lifestyles or behaviours are more or less likely to develop the condition. While these studies are useful for spotting trends, they aren’t designed to tell us about cause and effect. But over time, multiple studies carried out in large groups of people have helped build a picture of the factors that seem to have the biggest impact – although this picture is not yet complete.

According to the researchers’ calculations, 65% of the risk for dementia comes from things we can’t change, such as our age, sex and genetic make-up. This review focuses on the things that we may be able to do something about, known as ‘modifiable risk factors’. The report names nine factors that may increase the risk of dementia:

  • hearing loss
  • low education
  • smoking
  • depression
  • lack of physical activity
  • social isolation
  • high blood pressure
  • obesity
  • diabetes

For each of these, the team calculated the percentage of dementia cases that could potentially be prevented if the risk factor could be eliminated.

The top three risk factors according to this calculation were hearing loss from mid-life, low education in early life, and smoking – with the researchers estimating that the number of dementia cases could be reduced by 9%, 8% and 5% respectively if these were removed. Overall, they estimate that if all nine of these risk factors could be completely removed, the number of people living with dementia could be reduced by 35%.

Putting information into practice

There’s no guarantee that someone who avoids all of these risk factors will definitely not develop dementia, but evidence suggests people may reduce their risk by doing so – and the calculation highlights what might help to reduce dementia prevalence across the population. There are some caveats: in an ideal world, no-one would have to worry about hearing loss, depression, or any of the other risk factors talked about in this report, but in reality it’s unlikely that we can completely eliminate all of these risks. But the report could be particularly helpful for policymakers to decide where to focus their efforts when developing prevention strategies.

It can be difficult to separate some of these risk factors. For example, we already know that obesity and lack of exercise raise the risk of type 2 diabetes, and that hearing loss can lead to isolation or depression. There is still debate about whether depression could in fact be an early symptom of dementia, rather than something that raises the risk of the condition.

Some of the research in the report is relatively new: the evidence suggesting hearing loss as a risk factor for dementia is still emerging, and we need more studies to get a fuller picture of how the two conditions are linked. Several theories have been offered: perhaps the extra mental effort needed to cope with hearing loss may cause the brain to be less resilient, or alternatively, the same biological mechanisms could be driving both hearing loss and dementia. We don’t yet know whether treating hearing loss early could help prevent dementia, so next we’ll need to see whether clinical trials can shed light on this question. Regardless, ensuring that hearing loss is treated appropriately is important for people’s quality of life.

While this report helps draw attention to the things we can do to reduce the risk of dementia, there’s still a need for better evidence – that’s why Alzheimer’s Research UK is investing substantially in this area through our Prevention and Risk Reduction Fund.

In the meantime, the best advice is that what’s good for your heart is good for your head: that means eating a balanced diet with plenty of fruit and vegetables, staying mentally and physically active, and keeping blood pressure, weight and cholesterol in check. For more information on how to reduce your risk of dementia, download our free booklet.


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About the author

Kirsty Marais

Team: Science news