Working memory: the surprising decline of dementia
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What is the main topic discussed in this episode?
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.
How has dementia prevalence changed over the past 40 years and what evidence supports a decline?
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 40 years. Jonathan Rosenthal is an international correspondent at The Economist. So just to give you an example, between 1988 and 2015, the share of older people with dementia fell by 13% a decade across six countries in North America and Europe. But perhaps even more staggering, in the 1980s, three in every 10 people in their late 80s 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
Yes. 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 60s or 70s, 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.
Why do age and cohort effects make dementia projections seem worse than they are?
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 10 to 15 times higher. But again, those genes 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. What do you mean by lifestyle though? Tell me about that.
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Chapters
5 chapters
1
What is the main topic discussed in this episode?
0:03–0:34
2
How has dementia prevalence changed over the past 40 years and what evidence supports a decline?
0:34–3:18
3
Why do age and cohort effects make dementia projections seem worse than they are?
3:18–11:05
4
What genetic and lifestyle factors are linked to dementia risk, including APOE4?
11:05–24:50
5
Which lifestyle interventions and public-health measures have been shown to reduce dementia risk?
24:50–24:52