Today’s headlines across the media were resounding upbeat, following publication of an article in the Lancet.
The BBC led with:
Whilst the Guardian added a slightly more cautionary subheader:
But are these sorts of headlines justified by the evidence that the researchers were summarising? You probably won’t be surprised to hear that the answer is ‘no’.
The Lancet article itself is a well-written summary of the current state of knowledge about some of the major, modifiable ‘risk factors’ for dementia, and gives some figures on how strong the correlations are between dementia and those risk factors:
Now, you could argue firstly about whether the headline term ‘lifestyle factors’ can really be applied to things like not having a high level of education up to the age of 18. But there are bigger problems with the headlines than that.
The authors of the Lancet article carefully point out that they have selected risk factors which have a plausible mechanism by which they could, perhaps, cause dementia. However, there is no evidence that these ‘risk factors’ are actually causing dementia. For example, depression in later life could just as easily be an early symptom of dementia as an actual cause of it — as could social isolation.
Similarly, there is also no evidence to say that reversing any of these risk factors is going to reduce your risk of developing dementia. The Lancet article’s authors again are clear about this. Does fitting hearing aids to minimise hearing loss actually reduce the chances of those people going on to develop dementia? We simply don’t know. To find out, we would need to carry out large and very long studies doing and measuring exactly that. Those sorts of studies are difficult and expensive — and although quite a few studies have been, and are being, done into interventions to help reduce dementia, so far there is precious little evidence of positive results.
To state, then, that ‘9 lifestyle changes’ can reduce dementia risk is simply not supported by the evidence.
It’s not all doom and gloom, though. Although dementia is a huge fear for all of us, I think that taking a look at the risk factors and figures in the Lancet article can help put things into perspective.
We’ve often pointed out at the Winton Centre that ‘relative risks’ make differences look big. The figures from the Lancet (all relative risks) could easily be translated into terms like ‘almost double your risk of dementia’. But what are the ‘absolute risks’ of developing dementia?
Well, obviously they change as we get older, and as ever getting a ‘baseline risk’ is very difficult. The Alzheimer’s Society quote a figure of 6% risk for the average 75 year old. So, we can put some of the figures from the Lancet into absolute terms from that baseline:
The line illustrates 100 people. Those marked in blue are the 6 that you would expect to develop dementia anyway, and the orange represents those ‘extras’ whom you would expect to find in each category (NB again — we can’t say ‘develop dementia as a result of…’ because we simply don’t know that). So, taking physical inactivity in later life — out of 100 average 75 year olds, 6 would be expected to develop dementia, but out of 100 physically inactive 75 year olds, 8 might be expected to develop it.
Even this is likely to be a bit of an overrepresentation of the risks, because the 6% baseline is actually across the whole populaton — including those in the higher risk factor groups — rather than the strictly comparative ‘person not in that risk group’ (eg. ‘physically active’ 75 year olds).
I think if you look at that graphic, though, you might think that your chances of developing dementia are perhaps not quite as scary as they felt when reading press coverage about it. And, to use another technique that we often comment on at the Winton Centre, you can frame that information verbally another way: out of 100 average 75 year olds you would expect 94 of them NOT to develop dementia (and even out of 100 physically inactive 75 year olds you would expect 92 of them to be dementia-free).
So how about reducing your risks through lifestyle changes? Well, there is, as the authors say in the Lancet, a plausible link between the factors they list and dementia — and we know that none of them are ‘good for you’ — so trying to reduce them is indeed a worthy aim and a good message to communicate. But promising ‘lifestyle choices’ to ‘reduce your risk of dementia’ is a promise that the evidence, as it currently stands, does not support.