That Neuroscience Guy - The Neuroscience Behind Dementia Risk

Episode Date: August 28, 2025

In today's episode of That Neuroscience Guy, we discuss the neuroscience behind why some people get dementia while others don't. 

Hi. My name's Olive Kirk Olson, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. So I got asked a really interesting question the other day. And just for the update, I'm currently in Hamilton. So if the sound quality is a bit off, it's because I'm sitting in a hotel room and I just helped my son move into his first year of university. But anyway, sorry about the sound quality. The question I got asked is, why do some people get dementia and other people do not? It's a really good question because, you know, some people get dementia. And in principle, you know, they shouldn't.

They've done everything right, but they still get dementia. And then you get people that have done everything wrong, if you will, and they don't get dementia. So on today's podcast, I'm going to tackle that question. Why do some people get dementia and other people don't? Now, we do have an entire podcast episode on dementia back somewhere, and we also have hinted that in other places. So I'm just going to give you a quick overview of what dementia is. Now, first of all, as we get older,

cognitive decline with aging is perfectly normal. And I've mentioned this in the past, but I always like to look at a class of second year and third year students and tell them that they're dying, and they're looking at me going, what? And the reality is from the time you're about 20 to 22, you start losing anywhere from 20 to 25,000 neurons a day. That's just part of aging.

And eventually you would lose all your neurons. Now, if you do the math and you figure we've got 86 billion neurons, start subtracting 25,000 a day, you realize if you live to 100, you still got a lot of neurons. But that does cause cognitive decline. So, you know, the trouble that we have with memory as we get older, for instance, is perfectly normal, all right. Being a little slower at some things is perfectly normal. But again, I've done an episode on aging, I think more than one now. There are some things that

stay intact. For example, it's clear that people can learn across the lifespan. So learning stays relatively intact. Now, some people, though, a subset of people basically progress to mild cognitive impairment. And what that basically means is that they have trouble. with memory, trouble with decision making, trouble with basic cognitive tasks. Now, that's not dementia. That's MCI or mild cognitive impairment. Now, not everyone gets it. The exact prevalence rates aren't 100% sure, but probably 20 to 30% of the population in North America by the time they're into their 70s will experience MCI. The reason MCI is as interesting, and it's something, you know, my own lab is doing a lot of research trying to detect MCI

because it's actually hard to detect. But the reason why it's important, I'll come back to that in a second, the reason it's important is it's a precursor to getting dementia, right? Now, the reason it's hard to detect, as I just told you, is that cognitive decline with aging is normal, right? So if your cognitive function starts to slip, guess what? We expect that to happen. However, there is this subset.

of people, right, that have MCI. Now, in terms of how many people progress to dementia, roughly the prevalence is about 1 in 10 around age 65, but that increases with age, right? By the time you get, you know, 85 plus, it's about 35% of people have dementia. Now, we have an episode on this, like I said a few times, and I just want to point out dementia, Alzheimer's for instance, is just a form of dementia. It's not separate from dementia. So Alzheimer's disease is a subset of dementia. It's the most common kind of dementia, if you will, but there are lots of other forms of dementia. In fact, the list is constantly growing. But Louis Body dementia is one, vascular dementia, and there's a whole lot more. Now, why does dementia occur?

The most common theories involve the buildup of tau proteins or beta amyloids. Again, I talk about those in another episode. Basically, these are things that start appearing in your brain and they shouldn't be there, right? These are plaques, if you will, just like plaque into your teeth that builds up. It's basically scar tissue is one way to think of them. And the buildup of that impairs brain function, all right? And yes, there are people thinking about how to clean up tau proteins or beta amyloids. The problem with that is they're very hard to detect. They don't really show up on MRI scans. Typically, you can only see them post-mortem. But again, there are some cool, there is some cool research out there where people are trying to detect tau proteins and

beta amyloids while someone's still alive. But why? That's the big question. You know, why does someone get dementia and someone doesn't? The biggest reason is one that's sort of beyond your control, it's genetics. You might be born and be more predisposed for dementia than someone else. For instance, if you have the APOEE4 variant on a gene, you're more likely to get Alzheimer's disease. But it's not completely guaranteed. If they detect that you have this variant of APOE, because there are other variants, those are APOE 1, E2, E3, if you have E4, you're more likely. But a lot of people that have APOEEEE4 never developed dementia. So, it doesn't mean that you have to get dementia.

And there's a lot of people that get dementia that don't actually have that variant. So it contributes to the likelihood, but it's not, you know, written in stone at that point. Probably the biggest risk factor is just getting old. After age 65 or so, the chances increase dramatically, right? But it's not a guarantee as well, right? A lot of people live into their 90s and they don't have dementia. you know, I've met a couple of people well into their 90s that are, you know, they don't even have mild cognitive impairment. They're completely sharp. So age does increase your chance. And the only thing I'd really speak to that is you have to remember that our lifespans have been artificially enhanced by modern medicine and modern food and everything else. So, you know, we're living a lot longer than we're designed to live, right? This is why our bodies start to fall apart is you basically run the course.

And so, you know, this is just this buildup of these plaques, for instance. You know, if you drop dead at 50, you might have a couple of them, but by the time you get to 80, you have a lot of those plaques in your brain. There are other factors. Brain health and cardiovascular factors are there. So things that damage blood vessels, high blood pressure, diabetes, high cholesterol, smoking, they increase the risk of dementia because they basically make your brain more vulnerable. These are things that weaken the brain, if you will.

and also a lot of people have what are called ischemic strokes or transient ischemic strokes t-IAs and these are really small strokes that you might not even notice you've had one but they also damage brain networks now that technically wouldn't be dementia at least in a classic sense but it would come across like that another big factor why people some people get dementia and some people don't is lifestyle and environment Regular physical activity, mental stimulation, strong social connections, healthy diet, good sleep, hearing protection, funnily enough. These are all things that can help you stave off dementia or lower your risk for dementia. And there's a lot of evidence for this.

A very interesting fact with dementia is that the prevalence of dementia is considerably higher in low socioeconomic status groups than high socioeconomic status groups. So people that are well-off tend to live better lifestyles because they can. They can afford better food. They can afford to do more things. They can afford to sleep more and thus less risk for dementia. You know, the risk factors are kind of obvious. Chronic stress, social isolation, like the impact of COVID here is going to be interesting to look at. Poor diet, excessive alcohol use, traumatic brain injuries.

These things can all increase the risk for dementia. There are neurological and biological processes. I've talked about these. These are sort of, you know, it's a bit beyond your control. But I've mentioned the protein buildups, amyloid plaques and tau proteins. So that's why some people get in some donas because they have a buildup of these things and other people don't. But, you know, other forms of dementia like Lewy body proteins build up,

and that leads to frontotemporal degeneration. You know, chronic inflammation in the body can help lead to dementia. So people that have rheumatoid arthritis are more likely to possibly get dementia. And last but not least, in terms of why some people get dementia, others don't, is that basically having what we call it cognitive reserve, all right, keeping your brain engaged and stimulants. so lifelong learning, mentally engaging work, social engagement, these things actually fight against the effects of dementia. So you can sort of build up this sort of like, it's almost like a savings account of cognitive ability, the cognitive reserve. And by doing these things,

as your brain gets damaged naturally, because it will, that's just part of the process, guess what, your brain is sort of protected because you have a cognitive reserve. And same with resiliency, right? Your ability to bounce back from things, you know, like, oh, okay, that was bad, but, you know, I'm just going to get on with it. If you're, if you can do that more, you're less likely to be susceptible to these changes because you fight back. You're like, all right, my memory's not as good as it used to be. So you know what I'm going to do? I'm going to do stuff to try to help my memory, you know, Sudoku or things like this, right? So that's kind of why some people get to mention others don't. There's these six primary

reasons. I'll just review them. Genetics, you know, it might be beyond your control. Age, brain health and vascular factors. Probably the biggest one you control is lifestyle and environment. You know, one that always has made me laugh is I have this slide when I teach my class on aging, and you're less likely to get dementia if your partner is well educated. So I guess if you're young and you're listening to this, make sure you marry someone that's well educated because it's going to help you fight off dementia. Again, that's. might be beyond your control, the neurological and biological processes, and of course, this idea of working on having a cognitive reserve and being resilient. Well, hopefully you find that

interesting. That's why some people get dementia and some people don't. Just promise me one thing. If you're getting older like I am, I've turned 55 not long ago, and you find your memory is starting to slip, do not panic. This is perfectly normal. All right. right. I've been tested multiple times. I don't have MCI or dementia. And I do forget where I put my car keys. It's a thing. All right. My name's Olive Kirk Olson. But before I sign off, don't forget the website, That Neuroscienceguy.com. There's links to Patreon. Thank you so much for your donations. If you don't know what it is, just Google it. Check it out. Chat GPT will tell you all about Patreon. But that money goes to graduate students in my lab and it helps them with grad school. None of

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