Preserving Cognitive Function As You Age, with Tommy Wood

In this episode we discuss:

• The history of Alzheimer’s disease and what it reveals about modern dementia research
• Why most late-onset dementia is heterogeneous and largely preventable
• The Lancet Commission findings on modifiable dementia risk factors
• Dr. Wood’s 3S Model of Brain Health
• Why retirement often accelerates cognitive decline—and how to redesign later life for brain health
• The difference between “brain training” and truly brain-stimulating activities
• How complex, coordinated physical activities outperform simple exercise for cognitive resilience
• Key nutrients for long-term cognitive health, including B vitamins, omega-3s, vitamin D, iron, and polyphenols
• What really matters most for sleep when it comes to protecting the brain

Show notes:

• The Stimulated Mind by Dr. Tommy Wood
• Better Brain Fitness podcast
• Better Brain Fitness Substack
• Better Brain personalized brain check-ups and expert coaching
• “Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission” by Livingston, G., et al.
• “Demand Coupling Drives Neurodegeneration: A Model of Age-Related Cognitive Decline and Dementia” by Turknett, J. and Wood, T.
• Attention Span by Gloria Mark
• BrainHQ
• ACTIVE Study, Seattle Longitudinal Study, Vitacog Study, B-PROOF Study, OmegAD Study
• Matt Walker’s QQRT framework
• Follow Dr. Tommy Wood on Instagram
• Dale Breseden on Revolution Health Radio- Episode 1, Episode 2, Episode 3
• Learn more about the Adapt Naturals Core Plus bundle or take our quiz to see which products best suit your needs
• If you’d like to ask a question for Chris to answer in a future episode, submit it here
• Follow Chris on Instagram or Facebook

Hey everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. This week I’m really excited to welcome Dr. Tommy Wood as my guest. He’s an associate professor of pediatrics and neuroscience at the University of Washington, where his research focuses on brain health across the lifespan. This includes therapies for brain injury in newborns, prevention and treatment of adult brain trauma, and the factors that contribute to long term cognitive function and cognitive decline, which is what we’re going to be talking about in this episode today.

Tommy has a new book out called The Stimulated Mind, which is a fascinating look at the primary factors that drive cognitive decline and the most important steps that we can take to preserve our cognitive function as we age. Tommy received an undergrad degree in biochemistry from Cambridge and then a medical degree from the University of Oxford and a PhD in physiology and neuroscience from the University of Oslo. He’s also the head scientist for motorsport at Hintsa Performance, overseeing health and performance programs for multiple Formula One drivers, he helped to found the British Society of Lifestyle Medicine, is head of research for the Dementia Prevention charity Food for the Brain, and serves as chief science officer for the brain health coaching company Better Brain. He’s the host of Better Brain Fitness podcast, and as I mentioned, author of the upcoming book The Stimulated Mind. So as you can tell from his bio, Tommy is a preeminent expert in this field. He’s also a fantastic guy. I’ve had him on the podcast before, and [he’s] really fun to talk to about this stuff.

We cover the history of Alzheimer’s disease and how that actually gives us some hints for how we should be approaching it, primary drivers of cognitive decline with age, [the] 3S model of brain function that he proposes in his book, why the relative lack of stimulation in the adult human brain made us think the brain couldn’t adapt or improve with age and what we’ve learned about that recently, why the concept of retirement is a mismatch for the brain, what the brain biologically needs and expects, how different types of exercise support different parts of the brain, the most critical components of diet and nutrient status that affect long term dementia risk, how sleep plays a role, and many other topics. This was a fascinating interview. I hope you enjoy it as much as I did. Let’s dive in.

Chris Kresser:  Tommy Wood, pleasure to have you back on the show.

Tommy Wood:  Thanks so much. Really, a huge pleasure to be back.

Chris Kresser:  So I am really interested to dig into this topic. You have a new book coming out called The Stimulated Mind, and you’ve been deep in this world for many years. It’s an interest of mine. As you know, I’ve had Dale Bredesen on the show several times, and plenty of others who specialize in cognitive health. But I really appreciate the particular focus of your work and of this book, because I think it promises to be empowering and give people practical tools they can use to evaluate their cognitive health and then improve it over time. So I think it would be helpful to start from a 30,000 foot view, because I learned some interesting stuff about the history of Alzheimer’s from you, and I think it’s actually important to understand the context before we dive in and start talking about the details. So let’s talk a little bit about the history of Alzheimer’s, and use that as a way to frame the discussion about how we can be proactive and prevent it.

Tommy Wood:  Sure. So, as you kind of mentioned, the goal of the book is really to help people understand a little bit about where the history of dementia and Alzheimer’s research comes from, because I think that tells us a little bit about how we think about the aging brain, which, luckily, is not necessarily true. Because we have a huge amount of agency and influence over our cognitive function pretty much at any age. And so there’s a little bit of neuroscience history in the book that kind of sets the stage. And then after that, the goal is to give people practical tools to understand their brains and then hopefully intervene as needed to minimize their risk of long term cognitive decline and dementia. The sort of story that I tell as it relates to the history of Alzheimer’s and actually neuroscience in general, and I think this is something that people maybe don’t realize, is that the way that we study the brain in general, is historically and still today, is we take slices of brain from somebody who has died, and we look at those slices, and from that we try to infer something about what their brain did when they were alive.

And this started with Ramón Santiago y Cajal, who shared the Nobel Prize with Camillo Golgi, as they sort of discovered the nature of the nervous system. That’s what they got the Nobel Prize for at the beginning of the 20th century. And around the same time that was when Alois Alzheimer was doing his work and describing what then became his disease. But it was all down to like, what can we see under a microscope? And the idea being that, based on how a brain looks under a microscope, we can figure out what that brain was like in real life. And still, the reality is that slices of brain don’t tell us very much about the human that that brain once belonged to. But we’ve become hyper focused, still on some of these things that were first described by Alzheimer under the microscope. And those things are important, right? We’re talking about amyloid plaques and tau tangles, and they do absolutely play a role in this process, but they’re not everything in this process. And there’s big gaps between what you can see under a microscope or even on a brain scan now and how that brain lives and breathes. But there was, as I was researching the history of Alzheimer’s disease, I found an interesting description about the first patients that Alzheimer had and his index case was a woman called Auguste Deter. And she was a Swabian housewife in her 50s who was institutionalized. Alzheimer was a psychiatrist and he spent time with her prior to her death, and then he looked at her brain after death. And that was where he first described plaques and tangles. And then there was a collection of patients who had something similar, some kind of very early onset, unusual dementing process that he treated, five or six cases. And then they kind of became collected together underneath the initial umbrella of Alzheimer’s disease by Alzheimer’s mentor, Emil Kraepelin, who was another psychiatrist. He put it in a textbook. This was Alzheimer’s disease. It’s unusual, early onset dementias as a collection, he sort of put them together. And retelling, certain retellings of the story suggests that Alzheimer wasn’t even sure these were all the same thing, actually. But they were just kind of lumped together under his name, which doesn’t necessarily mean that this isn’t important for what we call Alzheimer’s nowadays, but what most of us think about when we think about Alzheimer’s disease, is late onset Alzheimer’s – much more sporadic, heterogeneous, influenced by a whole variety of environmental factors, that’s very different from what Alzheimer originally studied.

And I just found it interesting that it’s possible that Auguste Deter didn’t actually have Alzheimer’s disease at all, didn’t have early onset Alzheimer’s related to one of the familial or single mutations that can cause early onset Alzheimer’s, like in the presenilin genes, or in amyloid precursor protein. Because people have looked. They’ve looked at sections of her brain that were left over from Alzheimer’s work, they’ve tested for the most common causes of early onset Alzheimer’s. And first there was a team who thought she had a mutation in APOE2. Then another team came in and retested it. They couldn’t find it. She also wasn’t APOE4, either a homozygote or a heterozygote. I think she was APOE3/3. So she actually had none of the genetic risk factors for what we now call Alzheimer’s disease. And people have hypothesized what it could have been. I think one of the more credible suggestions is she had neurosyphilis, which actually creates amyloid plaques in the brain that look very similar to Alzheimer’s disease. But it doesn’t necessarily change what we think about Alzheimer’s disease now. But I just think it’s interesting that the first patient with Alzheimer’s disease may not actually have had Alzheimer’s disease at all. It also tells us that there are a whole host of things that can drive these dementing processes and look very similar when we look at the brain under a microscope, that aren’t this one disease as we sort of think of it.

Chris Kresser:  Right. Which could also explain why the conventional approach of trying to find a silver bullet medication that’s going to be effective in all of these different cases is probably misguided and has not borne significant fruit despite 20 or 30 years of effort. This is probably a good segue into my next question, which is, what are the primary drivers of cognitive decline with age? And how do these vary across individual cognitive function, population trajectories, biological causes, and societal and psychological causes? Because we don’t live in a vacuum. These factors are all interacting all the time in our unique individual context. So how do we make sense of that? It seems important if we’re talking about how to prevent and mitigate cognitive decline.

Tommy Wood:  Absolutely and you and most other people will be familiar with this idea that right now we think that the majority of dementia cases are potentially preventable if we address all the risk factors that contribute to them. The Lancet Commission report, run by Professor Gill Livingston, [says] 45 percent, other analyzes have suggested maybe even upwards of 70 percent, not all of that is driven entirely by lifestyle and environmental factors we have control over. There’s some socioeconomic and societal factors that certainly contribute. But were we to address all of those, it seems like the majority of cases, particularly, I think Alzheimer’s disease and vascular dementia, which make up 70 to 90 percent of dementias, would certainly fall under that umbrella. So when you start to think about all the things that you mentioned there, and within each of those buckets you mentioned, there could certainly be dozens of additional risk factors, biological pathways, all these things that kind of come together. And I think that explains why there’s this well worn adage that neurologists say, which is, “When you’ve seen one patient with Alzheimer’s, you’ve seen one patient with Alzheimer’s,” right? Because they’re all so different. And I think that’s exactly because of what you said. There were all these different things interacting that result in one particular trajectory or experience of cognitive decline.

And so the field is digging into each of those pathways and all those other things individually. And there are certainly approaches such as Dale’s, where you try and tackle as many as possible in one go, and that’s certainly going to be important the further people are down that trajectory. But to try and help both me to understand as well as other people to understand it, I’ve kind of created a model of how I think these factors group together in terms of the sort of mechanisms and pathways that they’re affecting, without having to get a degree in biochemistry to sort of understand them individually. So towards the end of the book, after I’ve gone through each of those sort of like big buckets of lifestyle, nutrition, physical activity, sleep, stress, etc, other environmental factors, the effect of sex, menopause, things like that, I sort of have this model of how I think these things kind of act at a high level which I call the 3S model.

So the three Ss are stimulus, supply, and support. And when I was kind of thinking about how all these things come together, I, as you know, enjoy physical activity. I’ve been an athlete my entire life, and so I think about things as I would think about, I think about the brain as if it were a bicep, right? And so this also translates over to most tissues and organs of the body, where the primary driver of its function is the stimulus or the demand that’s placed on it. We can think about this in terms of immune function. We can think about this in terms of liver function, muscle function, and brain function. So sort of the core thesis of the book is that how we use our brains is the primary determinant of their function. So stimulus is therefore sort of like that key bucket. And this is everything from social connection, complex skill learning, education, all those sort of components of how our brains develop skills and learn things and then go out into the world and use them and connect with others. And there’s lots of different ways that you can think about how to do that. Then when you’re stimulating a tissue such as the brain, the first thing that happens is that the activity in certain networks of the brain associated with that stimulus, a second language, the activity in the neurons and the astrocytes drives a dilation of the local blood vessels to supply additional blood flow, oxygen, [and] nutrients through a process called neurovascular coupling. So you need a healthy cardiovascular system and vascular system in order to kind of bring these things into that area of the brain as it gets stimulated. That’s why there’s actually a huge overlap between Alzheimer’s disease and vascular dementia. Most cases of Alzheimer’s have some vascular disease. So that’s where aerobic fitness and other aspects of heart disease risk become important. Then you need some kind of supply of metabolic substrate or energy, right? So glucose regulation is important. Could be lactate, could be ketones. Certainly, there are many options, and you need some core supply of nutrients that are needed to kind of run that whole system. And then the final bucket is support. So you’ve stimulated an area of the brain that’s brought in all the things that it needs in order to drive neuroplasticity and sort of cement new connections and drive function, you need a period of adaptation. And to allow that adaptation to occur, you need rest and recovery so sleep is a critical component of that.

There is also trophic support. Hormones and trophic factors that you might release through exercise or similar become important there. But then we also want to avoid things that inhibit that adaptation process. So you might think of excessive alcohol, smoking, air pollution, other sources of chronic inflammation, chronic stress that might do that. And all of those three buckets interact, right? So when you stimulate the brain, you actually create a greater pressure for sleep the following night. There are nice studies in older adults where you have them do brain training, and then they sleep better because you’ve kind of driven that, just like when you stimulate certain parts of the brain, they bring in additional blood flow and oxygen. So the reason why I think about it like that is that rather than having to think about 100 things or 40 things or 37 things to improve your brain health, you can think about what’s the one thing within all those buckets or areas where I maybe have the greatest amount to gain. Because when you change that one thing, whatever it is, you improve your sleep slightly, or you start a new exercise program, the whole system actually shifts. And you see that, right? You sleep better. You’re more social, you’re more likely to engage in cognitive activity. Your blood pressure improves. Your blood sugar improves.

So you can certainly go down into all those different sort of mechanistic pathways. But I sort of argue earlier in the book that the reductionism in neuroscience, kind of digging deeper and deeper and deeper hasn’t really gotten us anywhere. So it’s time to kind of like step back and think about these bigger, common pathways, and then we have a better idea of how we can intervene.

Chris Kresser:  Yeah, I used to have this conversation with my patients a lot, because people would come in understandably terrified about dementia or Alzheimer’s. Maybe one of their parents had it or it runs in their family. And part of the conversation was first kind of establishing where they sit in that spectrum of risk. Genetics are one thing, of course, APOE, we’ll come back to that in a second. But even with strong genetic risk, as you mentioned earlier, we know that environment plays a very important role. It’s not something that is deterministic just from having the gene like cystic fibrosis or something like that. There’s still a big role that environment plays and oftentimes people would be kind of seeing headlines about how common dementia and Alzheimer’s is and growing incidents, but not really realizing that they are well ahead of the curve or the distribution of the average American population, like sedentary, highly processed and refined food diet, smoking, cigarette smoking, all kinds of risk factor. Poor metabolic health, high blood sugar, poor cardiovascular function, etc. That’s kind of very common in the US right now. And that’s not to say that people who are doing everything right can’t ever get dementia, but certainly the risk is much lower.

So let’s talk a little bit about this interesting data recently that the age specific incidence of dementia has actually been decreasing rather than increasing, even though the overall burden, societal burden of dementia is projected to increase. What do you make of that?

Tommy Wood:  Yeah, this was also slightly surprising to me. It was first pointed out to me by Professor David Smith. He used to be Department Chair of Pharmacology at the University of Oxford, and he ran the vitacog study where individuals with elevated homocysteine were given homocysteine lowering B vitamins, and it slowed brain atrophy and slowed cognitive decline. So one of the first studies to show that we could intervene at that moment.

Chris Kresser:  Causal relationship there too, because at some point there was also a question of whether that was just correlation and not causal.

Tommy Wood:  Yeah, absolutely. And so he was one of the first people to really show that. And he mentioned this, and I sort of dig into it a bit further. And there’s actually several studies that show this. So there’s two competing parts that don’t necessarily make sense initially, but I think they can be very helpful for us to kind of understand the bigger picture. So the first is that, yes, dementia burden is continuing to increase and is projected to increase double or triple in the next two or three decades. And a large part of that is that we’re living longer and we’ve become better at treating other things that would kill us first, especially heart disease, and also increasingly good at treating certain cancers. So that just makes it more likely that we’ll live long enough to get dementia before we die of something else, or we’ll treat another chronic disease long enough that we will then get dementia as well. And that sort of like, that’s what people focus on, is this dramatic increase in the burden of dementia. But when you look at the age specific incident, so what this means is, at 60 years old, how likely are you to have dementia and/or at 70 years old, how likely are you to have dementia or be diagnosed with dementia? And that has been decreasing in multiple populations, including the US. Since cohorts of people born in like the 1920s or 1930s, it’s actually been steadily declining. So one study, the Framingham Cohort Study found that, that across a sort of decade, birth cohorts, born in the 1930s, 1940s, 1950s, age specific dementia incidences were decreasing and brain volumes were increasing. And I think a lot of that is to do with changes in terms of like food accessibility after the Second World War and the Great Depression, improvements in treating heart disease and preventing heart disease. And that’s actually what people think is a big driver of this is because the risk factors for heart disease and dementia overlap so much that because we’ve become better at treating heart disease, that’s translating to improvements in dementia incidence.

And so there’s data from the US, but then there’s also several studies in the UK, other European countries that show this. And there was a meta analysis that was published a couple of years ago that essentially showed that across these multiple populations. So that’s, I think, useful to know, because yes, now people are suggesting that we’re going to get an uptick again in age specific incidents, because metabolic health, for instance, overall, is declining, although that may not happen with GLP-1s and other things that are coming in. We may be able to hold that off. But I think that’s really important to know, because it shows that, at the population level, if we intervene, such as with treating heart disease, or other improvements we can do at the population level, we can then see population level changes in dementia incidence. So that gives us hope that if we can actually get people to do some of the things that we talk about in terms of decreasing dementia risk, you can see a meaningful decrease in dementia burden at the population level.

Cognitive decline is not an inevitable consequence of aging. In this in-depth conversation, Chris Kresser and Dr. Tommy Wood discuss how brain health is shaped by lifelong patterns of stimulation, metabolic support, and recovery—and how individuals can meaningfully reduce their risk of dementia. #ChrisKresser

Chris Kresser:  Yeah, I think that’s a really helpful insight. And I want to, for the rest of the show, talk about how to do that on an individual level. And in particular, I mean, people who’ve been listening to this show for a long time have heard me talk about exercise, diet, sleep, stress, alcohol, social connection quite a bit. And so I’m not saying we shouldn’t talk about that as well, but I mean, on the one hand, this should be encouraging news, right? These are all pleiotropic interventions in a sense that they’re not just going to help. It’s not like you have to do this one set of things to prevent dementia and then a completely different set of things to prevent metabolic disease, and then a completely different set of things to prevent cardiovascular disease. Thankfully, that’s not the case. They’re all the same things for the most part. However, you do have some specific things that primarily apply to dementia and cognitive health and things that we might want to be thinking about as we age that are specific to the brain and protecting our cognitive function as we age. So if you’re willing, I’d love to focus there.

Tommy Wood:  Great.

Chris Kresser:  And of course, the name of your book hints at what that is, The Stimulated Mind. You already alluded to it in terms of thinking about hypertrophy and thinking the brain as a muscle and what we need to do to protect it as we age. Because I think that’s a really interesting conversation that I haven’t had a lot on this show. And we can tie that into retirement as a mismatch, one of the many other areas in the way that the modern world is mismatched with our biological history and imperative, you could say. Because I think that’s maybe not new, but a unique part of the equation that people haven’t heard as much about.

Tommy Wood:  Yeah, so you’re right. This is sort of where a lot of my thinking has gone in terms of how we might start to tackle this on an individual and a population level. And some of it stems from, or a lot of it stems from work that I’ve done with my colleague, Josh Turknett, who’s a neurologist. We wrote a paper about this sort of a theory of age related cognitive decline based on cognitive demand that we published a few years ago. And to kind of step back even further for a second, when I think about all the different sort of areas in which I do work. So one is obviously thinking about long-term cognitive function, cognitive decline. I also work with high level athletes and performers, and then do work with the developing brain to try and ensure babies get the best possible start to life, even when things maybe weren’t optimal around birth. They didn’t have the best start. And in all those different areas, what you see, I think, as the stimulus, really, as a broad category, is the primary driver of how those brains function. So that, I mean that can be thinking about the activities that seem to slow the rate of cognitive decline, or maybe even improve cognitive function in older adults. It’s the things that determine the skill level of an athlete, and it’s also what seems to be the most important factor in terms of early life brain development.

And when you think about cognitive trajectories over the lifespan, the way that we often sort of quantify stimulus in early life at least, is education. And this, I think, kind of sets up the whole picture. So cognitive function, and we’re talking sort of average cognitive function from like a cognitive function battery, right? So this encompasses processing speed, verbal fluency, working memory, all those sort of like core cognitive functions that we could measure. Cognitive function seems to peak at around the time that we leave formal education. So the higher the level of educational attainment, and the longer we spend in formal education, the higher and the later the peak of average cognitive function. That doesn’t mean that you need to be in the formal education system in order to get these benefits, right? It’s just all about learning, and your primary job being to shape your brain through novel inputs and skill development and knowledge acquisition. That can happen anywhere. But the way that these studies are done, it’s easy to collect data in terms of formal education.

So all of that suggests that the more time you spend where the primary thing you’re doing is giving stimulus to the brain, you increase this sort of like average capacity of the system. And there are some socioeconomic and other factors that kind of go into that. But still, overall education seems to be this primary driver of early development. And then after that, the trajectory of decline, again, seems to be related to what we’re doing with our brains on a day-to-day basis. So there are big meta analyzes and individual studies that show that those who have more complex and stimulating work, they have more of a social component, they’re problem solving, they’re learning new skills, it’s highly varied. Those individuals both have a slower rate of cognitive decline, and they have a lower risk of dementia. And you see something similar from the skills that, or the hobbies that people have, more cognitively stimulating skills, complex sports, reading, lectures, that kind of stuff, again, that seems to change the trajectory of cognitive decline. And then, as you mentioned, retirement seems to be the point that, across several population studies, at which cognitive function, or cognitive decline accelerates the most because we’ve removed the primary stimulus that our brains get, which comes through work. And again, that’s a social and a work-related thing. So across the entire lifespan, how we use our brains really seems to be the driver of how our cognitive function is built and then maintained.

Chris Kresser:  Yeah, that’s pretty fascinating, because it’s something that, historically, I don’t think was really on people’s radar. Maybe, in retrospect, my parents’ generation noticed that or thought about that once they retired. But it wasn’t, I don’t think it was part of the discussion at all. It was just kind of baked into the societal fabric, that you would work and retire and live the good life starting at that point. But I think these days, people are thinking about it differently, and then maybe like a lot of people I know, and even myself, you think about maybe transitioning into something different, like a different activity, or something that’s engaging and interesting. Maybe you’re not working for money in the same way that you were before. But it’s not like sitting on a lawn chair out in the yard for the remaining 20 or 30 years of your life or whatever it is.

What are some of the critical factors? You mentioned social connection. You mentioned learning. But there’s also all these programs that are sold to improve cognitive function, like, what should people be thinking about? Is it mostly just staying engaged and being a lifelong learner and continuing to use your brain in those ways, or should they also be considering training their brain in the same way that you go to the gym and train your muscles and in order to preserve muscle mass and avoid sarcopenia?

Tommy Wood:  I think we can do a bit of both. And the whole field of brain training is certainly very interesting, and maybe I’ll start there, and we’ll go into the other things. But it’s been very contentious, brain training has, over the decades, with good reason. Because what would happen is this would be a relatively simple game, essentially, on a flat screen, which is very different from the multi-sensory, cognitive stimuli that our brains are used to receiving and adapting to. And then when you got better at it, it didn’t really seem to transfer to anything else. So you can be better at the brain training, right? You can be better at the game, but that’s not what anybody really cares about. You care about the other things and using your brain out in the real world. So we need to make sure that what we’re doing really is actually stimulating our brains in the right way. So the kind of, the clichés, do the Sudoku, do the crossword, that kind of stuff, that’s probably not at the level that we’re really thinking. And so one of the ways I think about this is, there’s a framework that Gloria Mark uses. She’s a psychologist. She has a very good recent book called Attention Span, and she thinks about all the different ways that our brains can engage in things. And there’s something that she calls rote activities, which require focus but aren’t cognitively challenging. And that’s basically what Sudoku and crosswords and things like that are, right? It feels nice to do them. Actually, they can be almost a break in their own way, but they’re not really sort of stimulating the brain tissue in any meaningful way.

But there is some evidence that certain brain training programs can work. And the best trial still is now almost 30 years old, and it’s called the ACTIVE Study. And one of the people who ran the ACTIVE Study was Sherry Willis. And she was married to Warner Schaie, who ran something called the Seattle Longitudinal Study, which was actually, we can talk about it afterwards, but the Seattle Longitudinal Study data from that showed that cognitive decline isn’t predetermined or the sort of, it doesn’t happen to everybody. It doesn’t actually happen to most people in the sort of, this was done in the 1950s, 60s, and 70s, and that was used to raise the retirement age in the US. But so an extension of the Seattle Longitudinal Study was the ACTIVE Study. And what they did is they took nearly 3000 people, they randomized them to four different groups, so they had a control group, and then they had three different cognitive training groups. So they had a processing speed group, they had a reasoning group, and they had a memory group. And they did just 10 weeks, it was just 10 weeks of training, and there were a couple of refresher sessions at like one year and three years. And they followed these individuals up for several years afterwards. And what they found was that all three training groups ended up with higher quality of life several years later. But the one that really seemed to make the difference was the processing speed training.

So this was, on a screen you’re presented with different challenges, and then you also have to respond to things quickly, sort of in the periphery. And the group that had processing speed training, they had significantly improved quality of life, greater ability to maintain activities of daily living several years later, and these are individuals sort of in their 60s, 70s and older. And then they were more likely to be driving several years later, they were less likely to have significant accidents where they were at fault. They were actually able to train processing speed and maintain it, and that translated over to real world improvements. That particular processing speed intervention is now called Double Decision, and it’s in a program called BrainHQ.

So there are some, and I have no affiliation with Brain HQ, but Mike Merzenich, who’s like one of the godfathers of learning and neuroplasticity, he’s one of the founders. And so there are some platforms that do have some evidence behind them. So if people are interested in that, they can certainly think about that. And obviously that platform has many other training modalities as well. But I do think that we could get even greater stimulus in a way that the human brain is used to receiving stimuli through other activities. So for instance, through what we would call coordinative or open skill physical activity. So when they do studies where they compare two different physical activities that have the same physical intensity, but different levels of cognitive complexity, both are helpful for cognitive function and overall health. But the one that has greater complexity seems to have a greater improvement. And you can look at hippocampus volume on an MRI scan, you can look at different cognitive functions, you can look at trophic factors that get released during exercise.

Chris Kresser:  Let me just interrupt and ask, what would be an example of that? I assume jogging is probably pretty low cognitive stimulation or capacity. You’re just putting one foot in front of the other and going. What would be an example of an activity that is higher cognitive capacity?

Tommy Wood:  Yeah. So you’re absolutely right. So sometimes running is, or jogging is used as that, the comparison. But the activities that have been studied are things like table tennis, badminton, dancing, like ballroom dancing, they’ve compared like running around a track to doing an obstacle course on the same track. So it’s anything, and I think especially if we’re thinking about processing speed, which is one of the primary functions that declines with age.

Chris Kresser:  You’re reacting. I’d imagine something like skiing where there’s obstacles, the terrain is constantly changing, you’re taking in a lot of different environmental input, snow surface conditions, everything else, or surfing or something like that, would be pretty high on the list as well.

Tommy Wood:  Yeah, exactly. So I think that anything that either requires you to constantly react to the environment like a board sport, or that requires you to react to other people and/or build strategies in real time. So ball sports, racket sports, those kinds of things, anything like that. Pickleball, right? Really popular nowadays. I think anything like that.

Chris Kresser:  I’m going to live a long time, Tommy. Surfing and skiing and pickleball are kind of, and mountain biking, which is similar, terrain, environmental input. In all seriousness, though, what about balance, too? I assume that affects the brain in a particular way as well. I remember reading some research about yoga and other other activities which, mountain biking, skiing, a lot of sports involve balance too. That has some benefit on the brain as well.

Tommy Wood:  Yeah, so it’s interesting, because often balance and stretching exercises are often used as control groups in some of these studies. So I think that just simpler balance exercises, yes, I mean, if you can spend more time standing on one foot and all those kinds of things, those are certainly going to be better. But compared to the much more dynamic balance required for complex yoga sequences, or skiing, or surfing, I think there’s definitely going to be a range and spectrum of the level of stimulus. So start, right. If you have a poor balance to start, I think you would start on that end with simple balance exercises. But ideally, you get to the point where you’re doing something more challenging.

Chris Kresser:  Then have someone try to push you over while you’re doing your handstand or your balance, or your tree pose in yoga. Make it more challenging.

Tommy Wood:  Yeah, many ways to do that.

Chris Kresser:  Yeah. Okay, so I said we’re not going to go into a total basic review of exercise, diet, sleep, stress, and all that stuff. But that doesn’t mean we can’t talk about those. Just as the case with cardiovascular disease, I talk with patients about diet, I’m going to give them specific things to think about as it relates to cardiovascular risk, right? Or if a patient has high blood sugar and metabolic issues, I talk about specific dietary things. If a patient has autoimmune disease, I might prescribe AIP or a specific diet for that. So what are the primary considerations in terms of cognitive function, dementia risk, when it comes to, let’s just say, not just diet, but nutrients, which might involve supplementation as well? We talked about homocysteine as a driving factor, and B vitamins, omega-3, certainly EPA and DHA. What are the primary considerations from your perspective?

Tommy Wood:  So that’s generally how I think about it. I think about sort of three overlapping components of diet that I think are the biggest levers. So one is overall energy availability, and that’s important at both ends of the spectrum. And there’s been some nice studies that have kind of modeled brain volume, which contributes to brain reserve, which is essentially just a fancy way of saying, how much brain do you have in your skull? Because the more you have, the more you can lose before you start to see significant declines in function. And we see it, both low energy availability, which is very common in the athletes that I’ve worked with, they’re not eating enough calories to drive all the repair and maintenance and adaptation processes that they ideally have. You see mood changes, gut changes, hormone changes because they don’t have enough energy in the system. I think this is important, because it makes me think that significant caloric restriction is probably not going to be the magic thing for your brain long term, because the brain will decrease its volume. It will use up, I mean, both acutely and chronically, it will use up myelin stores as an energy source if there’s not enough available, and you won’t, you sort of invest in that tissue, in the same way.

And then at the upper end, like you said, metabolic disease. We know individuals with metabolic syndrome or obesity have more rapid loss in both brain volume and brain function. So energy balance is important. And then there are core nutrients that I think are best connected. We have the best evidence for them being related to risk of cognitive decline and dementia. So B vitamin status, particularly homocysteine lowering B vitamins. So B12 and folate, but also B6 and riboflavin, vitamin D, omega-3s. Iron status is critical. So anemia is a significant risk factor for dementia, as is polycythemia. So elevated hemoglobin or hematocrit, that’s usually related to obstructive sleep apnea. Those sort of consistently have been shown to be associated with an increased risk of dementia, and they may compound and interact. So the best example of that is omega-3 status and homocysteine.

We mentioned earlier the Vitacog Study, where individuals with elevated homocysteine were given homocysteine lowering B vitamins, and it was like folic acid and cyanocobalamin. It wasn’t like fancy methylated anything. Even this was enough to have a significant benefit in these individuals. But they found that only those who had adequate omega-3 status benefited from homocysteine lowering when it came to changes in brain volume and cognitive function. And this has now been repeated in three different studies, at least. So the B-PROOF Study found the same thing, where they gave B vitamins, and the OmegAD Study found the opposite. So they gave omega-3 fatty acids, but those who had elevated homocysteine didn’t benefit. And so exactly like you said, for a long time, people like, well, lowering homocysteine or giving people B vitamins doesn’t work. Well, that’s because they didn’t look at omega-3 status, whereas those two, and vice versa, oh, giving fish oil doesn’t work, but that’s because people weren’t looking at homocysteine. So we know that those interact, and that’s probably because putting that DHA in that neuronal cell membrane or in that synapse requires it to be attached to part of a phospholipid. It requires methylation for that whole process to work. So if your methylation is impaired, you can’t get the DHA where it needs to go.

So I think those are the most important nutrients. Other things that we know are important, magnesium, zinc, right? They’re important for neuromodulation. Antioxidant polyphenols and their sources, particularly berries, come up again and again, as well as other things like lutein, zeaxanthin, astaxanthin, those seem to be really important. So like, those are maybe some of the core nutrients we have some of the best evidence for. And then, like, the third component of diet I think about is pattern. So like, what’s the way that I can eat in order to make sure I get those nutrients and I remain sort of in good energy balance? And there can be hundreds of ways to skin that cat. But as long as you’re touching on those other things and it’s sustainable, then you’re hopefully getting most of the work done.

Chris Kresser:  Right. And then, for some people, supplementation may be necessary, even if they’re eating a healthy diet.

Tommy Wood:  Exactly.

Chris Kresser:  And I’ve seen this in my practice over and over. It can depend on a lot of different factors. One of them, in particular with homocysteine, is genetic polymorphisms. People with MTHFR polymorphisms can be more likely to need additional folate unless they’re eating a very high folate diet with chicken liver, for example, or lots of dark leafy greens, like kale. And then omega-3s I think are a little bit easier for people who are willing to eat cold-water fatty fish and seafood regularly, which I really enjoy, but I had a number of patients who just really didn’t like to consume seafood, or particularly that kind of seafood. And I ran omega-3 testing on everybody who I saw, and I just saw a paper published that said 75 percent of Americans have a low omega-3 index in their blood. And that tracks pretty similarly to what I saw in my practice. Even though my typical patient is way more engaged in this stuff than the general population, I still saw more people than not having suboptimal intakes of omega-3 in particular. So definitely something to test. You can test for these nutrients. You can test for homocysteine. These are pretty simple tests that you can get nowadays. So there’s no reason not to take a look and pay attention to that stuff.

Tommy Wood:  Yeah, I think, as what’s good, omega-3 testing, you might not necessarily be able to get through your doctor, but everything else, right? Homocysteine, blood sugar, vitamin D.

Chris Kresser:  B vitamins.

Tommy Wood:  Iron.

Chris Kresser:  There’s some nuance in how you interpret those, but you can get those tests for sure.

Tommy Wood:  Yeah, so that’s, and then, like you said, if you need to supplement I think people absolutely should.

Chris Kresser:  Yeah. What about, if I were to ask you the same question about exercise and sleep, what are the nuances for cognitive function? In your book, you talk about different types of exercise affecting different types of the brain. And then for sleep, what is the most important factor? Is it duration? Is it quality? Is it chronotype? Is it something else?

Tommy Wood:  Yeah, so for exercise, the simple answer is, so we kind of covered some of that coordinative stuff. And I think that that’s a great bang for your buck, because you’re going to hit certain types of strength, you’re definitely going to improve aerobic fitness. So I think those exercises are really kind of multi-component. And people who don’t want to spend all their time in the gym focusing on a ball sport or a board sport or a team sport of some kind, it’s going to get you a lot of the way there, if you’re doing it regularly. More broadly, it looks like activities that have more of an aerobic component, or are on that kind of spectrum, going all the way up to high intensity interval training. But those kinds of modalities, they seem to be particularly good at supporting or improving the health and function of the gray matter, especially the hippocampus, which people will know is critically affected in dementia, is important for memory. And then resistance or weight training exercises seem to be particularly beneficial for the white matter. And in randomized controlled trials, where they have people do a strength training program, they see improvements in white matter structure, then also improvements in executive function and processing speed, for example, because the white matter is critical for that.

So some combination of those things is probably going to be important, right? You need to maintain aerobic fitness, some intensity is important, because lactate seems to be critical. It’s the messenger from exercise to the brain to produce trophic factors like brain derived neurotrophic factor. That seems to be intensity driven. There was actually a very nice study that came out recently where they had individuals do what was quite a significant training intervention. The high intensity interval group did the Norwegian 4×4 protocol, three times a week for six months. And so, if anybody hasn’t heard of that, that’s four minutes at 85 to 95 percent of maximum heart rate on a treadmill with a three-minute break times four, and they did that three times a week. And anybody who’s done that before will know that that is not something you necessarily want to do three times a week. But when they did that for six months, and activity went back to baseline afterwards, because they track that as well. Five years later, they had maintained improvements in hippocampal structure and function after doing that training protocol.

So that seems particularly beneficial, some aerobic work, ideally includes some intensity, because you’re going to release some factors like lactate that seem to be these sort of messengers to the brain to improve some aspects of function. And then some resistance training. And that’s probably, the minimum effective dose from randomized control trials, seems to be like one to two sessions a week, six to eight exercises covering the whole body, three sets of eight to 12. Very, very basic program. So it certainly doesn’t require Herculean efforts.

Chris Kresser:  I think people get overwhelmed by all of the fancy options with strength training that are available now. And look, if you’re into that, that’s great. There’s so many different kettlebells and resistance bands and balance and strength and mobility stuff. And if you’re into that, and you want to go down that road, that’s fantastic. But I think it can become a blocker for some people. And really, I just saw the study, I imagine you saw it, that kind of overturned, or at least contradicted the typical idea that you have to lift really heavy weights to build muscle. And that actually you get hypertrophy even just training close to failure, whether you’re lifting heavier weights or lighter weights. And for most people, lighter weights are going to be better because it’s less risky. There’s less potential for injury, especially if you don’t have good technique, or you’re not working with a trainer. I like what you just said, because it’s simple. Just do six to eight different exercises, eight to 12 reps, with an amount of resistance that is close to failure by that 12th rep, and do that a couple times a week, and that’s all you need to do.

Tommy Wood:  And yeah, that’s interesting. And these are machines in the gym, right?

Chris Kresser:  Right, you don’t need to do Olympic training.

Tommy Wood:  Doing quats, or deadlifts, or yeah, exactly.

Chris Kresser:  Clean and jerk, and CrossFit style workouts. I also, I mean, I’m going to reveal my own personal preference here. But I’m a big fan of outdoor activities and sport because they tick so many boxes. You have a social element often, you’ve got what you were saying, the coordination and balance aspect. You have the processing thing, because you’re interacting with your environment in some way, whether you’re mountain biking or surfing or skiing or doing something else, playing Ultimate Frisbee, watching for the frisbee. And I think that people are more likely to stick with those types of activities because they have an element of fun. It’s not just another chore that you need to do. You can look forward to it. And speaking of brain function, I’m just a recreational skier, but I work with a coach. And every time I’m out skiing, I’m really thinking about what I’m doing and how I’m trying to improve, and I’m always working on something. That keeps it more fun and more engaging for me, but I think it’s also better for my brain, because I’m not just cruising down the mountain not thinking about anything. I’m actually really paying close attention to my physiology and anatomy, and making slight adjustments, sensing into what’s happening in my body in relation to the snow conditions and the visibility and everything else. And it just adds a level of richness to it that I don’t get from just running on a treadmill, for example.

Tommy Wood:  And I think that in general, people would feel like you do something like that, like that skiing, we’ve kind of got this idea that that’s not enough, right? You then also have to go and hit the treadmill, and then you also have to lift weights several times a week. And in reality, that doesn’t seem to be the case. And I say this as somebody who spends an hour plus in the gym every day. I know that I’m well beyond what I need to do and I do it for other reasons, because I enjoy it. But it doesn’t actually require that much, and it can be all made up of activities that actually you just find fun and they’re social, and it just happens to be that you get a workout at the same time.

Chris Kresser:  Yeah, yeah. I mean, and there’s different ways to ski. You can ski just standing straight up and cruising down the hill and not getting much of a workout. Or you can ski where you’re doing carve turns trying to get your hip to the snow. And I can tell you, after like 10 runs of that, my legs feel like I just did squats and deadlifts. Yeah, for sure. And same for mountain biking. Or, I mean, certainly, if you’re talking about Nordic skiing, that’s one of the most intense cardiovascular workouts you can get. There’s so many different ways. But I think in general, finding something that you really enjoy. Being in the gym, that’s awesome. But for a lot of people, it could be an activity that is fun, that’s challenging, where they’re trying to achieve some level of mastery. And then I think, bonus is outdoor, because you get exposure to sun and fresh air, and also with other people, because then you get a social element as well. You’re just checking so many boxes there. And I think it’s, I mean, I love going up to the ski hill and seeing, I frequently see people like well into their 80s, couples, groups, skiing together. And I just, I think it’s so great.

I mean, I’m sure with pickleball too, there’s a group of people who play where I play, and they wear these shirts that say “pickleball saves lives.” It’s just hilarious. I think it does save lives. It also keeps chiropractors and physical therapists in business, because you have so many people, elderly people, playing and doing things with their body that they haven’t done in years and maybe shouldn’t be doing. But it’s all good. It’s like people really engaged in a way that I think they wouldn’t be otherwise, in physical activity and social element.

Tommy Wood:  Yeah absolutely.

Chris Kresser:  All right, so sleep. Sleep was the other thing. So what are the key drivers or things that people should be really thinking about there?

Tommy Wood:  Yeah, so I think that one of the most useful frameworks for thinking about sleep is something that I’ll steal directly from Matt Walker, which is his QQRT framework. Maybe we’ve talked about that before. So quality, quantity, regularity, and timing. And in general, we’ve tended to focus on quantity and quality. So how long are you spending each night of sleep? And like, how good quality is that sleep. And I think in general, those who have good sleep hygiene and a good sleep routine will actually tick all of these boxes in one, or cover most of their bases. I think sometimes we’ve become so hyper-focused on sleep and we collect so much data on our sleep, and actually those data aren’t necessarily that good, and that influences how we feel and perform, maybe even more than our sleep does sometimes. But there was a recent study that looked at all these different components, and they found that regularity was maybe at least as important, if not more important, than some aspects of quantity and quality. So you need enough, it needs to be good quality. But there’s definitely a timing between the different balance of stages of sleep. So like more deep sleep earlier in the night, and more REM sleep later in the night. And those have a circadian component. So if you’re sleeping at a different time of day every night, then your deep sleep isn’t as well timed to when your body expects to be in deep sleep, and REM sleep similarly. So that seems to have an impact too. A regular bedtime as much as possible, and a regular wake time seems to be important.

The final component is timing, which is like, when are you sleeping relative to your chronotype? I don’t focus on that as much, because most people can’t change when they sleep that much, right? You have to get up and go to your job. So it can become a thing that people get really worried about, because they’re a night owl, but they have to get up in the morning. Or they still have to create a regular sleep schedule. And I think if you do that, you can hit all the other ones, and you’re going to get most of that benefit. So the answer is, you want as much as possible, as high quality as possible, and as regular as possible. But I think that sometimes the goals are so lofty that we think that we’re not sort of hitting them. It’s the same with exercise, right? We assume we have to be in the gym every day and that kind of stuff, and we assume that we need eight hours every night. And if we wake up a few times in the night, then that’s going to be a disaster. If occasionally we go to bed a bit late, that’s going to be a big problem. And in reality, the evidence suggests that sleeping less than six hours every night, that’s where dementia risk really starts to increase. Relying on alcohol and sedatives to get to sleep every night, that’s where risk increases. Regularity is kind of like plus or minus 30 minutes to an hour either way. So I think we have, yes, sleep. I mean, sleep is so critical, and sleep was actually left out of the modifiable factors that contribute to dementia risk in the The Lancet Livingston report, which I think many people were quite surprised by, because we know it’s so critical for long term brain function and dementia risk.

Chris Kresser:  Even short term brain function, I mean, you’ve seen studies of just one night of impaired sleep can really affect cognitive function, decision making, food cravings, a whole range of factors.

Tommy Wood:  Yeah, so we know it’s important. It’s surprising that wasn’t included. But I think that the quantity of sleep loss does need to be fairly high for us to really see an increase in dementia risk. And just to kind of, like that point about one night of sleep loss, because, like, sometimes we have a bad night of sleep. We’re traveling. We have kids, other things, something wakes us up. It’s really interesting that when you look at meta-analyses of studies where they stop people sleeping, or they force them to be sleep deprived, is that with one night of poor sleep, the biggest thing that changes is your mood. So your function may change slightly, but actually, most of it is you just have a poor perception of how you’re performing. Whereas, if you actually measure how people perform, they perform about the same. And this is just like one night. If this went long term, of course, it would have a bigger effect. But your speed might decrease, or processing speed might decrease slightly, but accuracy doesn’t change. So you’re a little grumpier and you’re a little slower, but actually the quality of your work is usually okay. And this was important to me personally, because previously, when I had a bad night of sleep, like immediately, I’m in my head:” I’m going to be terrible today, I’m going to be slow,” and all that kind of stuff. And actually, you can maintain function pretty well. Of course, it stacks up over time. And so some of it is genuinely in our heads, but over time, this can have a big impact.

Chris Kresser:  Some of the good cognitive behavioral therapy, CBT for sleep programs are really good about that, I think. They’re really just focused on talking people off of that ledge. If you don’t get a good night of sleep, let’s challenge this belief, like you just said. Does that mean that the next day is going to be a disaster? Does that mean that I’m going to not perform well at work or in my sport, or whatever it is? Because then that can become a self-fulfilling prophecy, right? You have anxiety about if you wake up in the middle of the night, even like, oh my god now I’m not going to get back to sleep and everything. You have the whole tape that starts going and then makes it impossible to fall back asleep, etc. So yeah, there are some good programs out there that address this for anyone who’s having trouble sleeping. And it can be helpful, because there’s the layer of just whatever’s going on that’s making it difficult to sleep, but then there’s the whole additional layer of the self talk and worry and the anxiety about not sleeping. And that’s modifiable. And then, of course, they feed back on each other.

So all right, well, this has been fascinating, Tommy. I’m really excited about this book, and would highly recommend that people go out and pick up a copy of The Stimulated Mind. And you also have a fantastic podcast of your own, Better Brain Fitness podcast. Where else can people learn about your work and stay connected to you?

Tommy Wood:  Yeah, thanks. So yeah, the book is The Stimulated Mind. TheStimulatedMind.com has links to all the places, and whenever and wherever you’re hearing this, wherever you buy books, it is available. I also have a website, DrTommyWood.comwhich has links to the book as well. Then there’s the podcast, Better Brain Fitness podcast that’s everywhere you would listen to a podcast. We also do it on Substack. So the podcasts are recorded live. If people use Substack, everything that’s on Substack is free. So BetterBrain.fitness. This is done with myself and Josh Turknett, who I mentioned earlier. And then all my podcasts and papers and things like that, I usually put on Instagram, which is at @DrTommyWood.

Chris Kresser:  Great. Well, thanks again, Tommy. It’s been a pleasure, and good luck with the book.