Working memory: the surprising decline of dementia
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Why is dementia prevalence actually declining worldwide?
The Economist. Hello and welcome to the Intelligence from The Economist. I'm Jason Palmer. Today on the show, the one person who hates Brazil's beloved digital payment system, and proof that emo music wasn't just a phase.
But first
There are lots of things we can all expect to lose as we grow older. Muscle mass, flexibility, deft use of the latest technology. But what really inspires fear is the possibility of losing memory, possibly losing oneself altogether to dementia. Happily, a close look at the data suggests there's steadily less and
less reason to worry. There has just been this absolutely astonishing decline in the rates of dementia over the past forty years. Jonathan Busenthal is an international correspondent at The Economist. So just to give you an example, between nineteen eighty-eight and twenty fifteen, the share of older people with dementia fell by thirteen percent a decade across six countries in North America and Europe. But perhaps even more staggering, in the nineteen eighties, three in every ten people in their late eighties had dementia, and that rate has now gone down to roughly one in ten. But it also seems as if a lot of the declines seem to be happening in rich countries, and actually part of the burden of dementia will be shifting to much poorer countries.
This is sort of surprising. There had been a sort of general narrative that the dementia problem was getting bigger, not smaller.
Yeah, so Jason, many people think it's going up. And part of the reason is just that the single biggest risk factor for dementia is age. That's as you get into your late sixties or seventies, the risks of getting dementia pretty much double every five years or so. The fact is we thankfully are living longer. And then you've got this huge baby boom generation coming through. So we've got a lot more old people in the pipeline, and just on that kind of Mechanical maths, people have been projecting these really astronomical increases. So much so that when I started talking to researchers who'd really dived in and actually looked at the rate per cohort, the age-adjusted rate, some of them just couldn't believe the numbers themselves.
One of them, a lovely fellow, Eric Stallard from Duke University, held off publishing for two and a half years while he just kept on going back over that data to check that he hadn't made any mistakes.
So then the instant million dollar question is what's behind the decline?
Oh, that really is the million dollar question. And researchers are still really puzzling over what the exact kind of mechanisms are, what's going on in the brain chemistry that is causing a lot of these dementias. So we've had this amyloid hypothesis that it's caused by these kind of tangles of proteins in the brain. But actually researchers are not sure whether that is the cause or a symptom of dementia. So that's the kind of no, we don't really know part of the answer. But the yes part. is that there is some really good data that's been coming out about what are the sorts of things that are associated with higher or lower rates of dementia. And that is where the really promising research is going.
Part of what we well, what I thought I knew about this is that the causes are at least partly genetic. So we know there is a huge genetic component to risk for dementia. And unfortunately, people can't change their genes. They can change their behaviors. Now, the particular gene that is associated with this is ApoE4. And the 25% of the population or so that have one copy of that ApoE4 gene have got a much higher risk of dementia. I think it's about two to three times higher. And a subset of them, about 2% of the population. Have got two copies of that gene, and the risk for them is about ten to fifteen times higher. But again, those genes are are very often just associations. So a lot of people who've got those genes don't get dementia, and a lot of people who don't have those genes do get dementia.
And that's where researchers have been looking into other factors, and a lot of that is down to lifestyle.
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