The #1 Dementia risk factor nobody talks about, and what to do

0:00Welcome to ZOE Science & Nutrition, where world leading scientists explain how their research can improve your health.

0:14Did you know there's an invisible disability that affects one in five people globally, that increases the risk of developing dementia by 500 % and has few treatment options and no cure? I'm talking about hearing loss. An astonishing half a billion people have hearing loss that impacts their ability to communicate and connect with others. And even more worrying, hearing loss cases are increasing fast, especially in younger people. For many, hearing aids and cochlear implants can be life-changing, but they can't help everyone. Hope, however, is on the horizon. Scientists around the world have been working tirelessly to develop new treatments for hearing loss.

1:02Leading the charge is Dr. Marcelo Rivolta, a professor of sensory stem cell biology at Sheffield University. He's on the cusp of a major breakthrough that could mean hearing loss becomes a thing of the past. By the end of today's episode, you'll understand the latest treatments, what the future of hearing loss looks like, and how looking after your hearing could reduce your risk of dementia.

1:31Marcelo, thank you so much for joining me today. Thank you. So we have a tradition here at Zoe where we always start with a quick fire round of questions from our listeners. And we have these rules that are designed to be really hard for professors. Right. And that is because the rule is you have to say yes or no or a one sentence answer if you have to. Are you willing to give it a go? Yep, let's do it. All right. Does hearing loss only really affect older adults? No. Are more of us facing hearing loss than ever before? Yes. Do people with hearing loss face an increased risk of dementia? Yes, that is true.

2:14Can hearing aids help everybody with hearing loss? No, unfortunately not. And finally, is a cure for hearing loss possible? We think it is, and we are developing something which we think could change the landscape. My podcast producer, Rich, has actually talked to me about how in his teenage years, he was running these underground raves. And that means now in his 30s, his hearing is actually damaged. And in my case, I remember the time that my son, aged about 11, so it's about seven years ago, joyfully showed me this app on his phone that played these high-pitched noises. and I discovered that not only I couldn't hear lots of noises that he said he could, but really depressingly, there were lots of noises my wife could hear that I couldn't hear.

3:01And I think since then, I've really noticed that in noisy restaurants, I can really struggle to hear people who are further away from me. I'm aware that I'm not quite as good as hearing as I was when I was 20. So then when you're telling me that hearing loss is becoming more common, I think that's very worrying. Why are we seeing this rise in cases? One of the reasons why it's becoming more common is because as a population we are aging. It's more common to have older people and we live longer. And one of the key factors that influence healing loss is aging. And as you said, that loss of the very high-pitched sounds that you tend to have from middle age onwards is just the opening of the door of more substantial healing loss that will happen later in life.

3:50And we, as a population, we are growing older, and it's more common to have older people. So that's one of the factors. But the other factor is we live in a noisier, in a more loud world. We have a lot of noise exposure. The use of headphones is prevalent. And sometimes we don't tend to respect the kind of the volume controls that most of the devices have. and the exposure to loud noises is really impacting the incidence of healing loss in general. And I'm interested that you already started talking about headphones. Are headphones safe or am I inevitably leading the path to becoming deaf if I'm using them?

4:34I think the headphones, the way that they are built, they have safety limits. The strong advice built by the manufacturers of what is safe and what is unsafe. But we tend to do, particularly the younger age groups, tend to use it beyond those safety limits because we get a more thrill of listening to very loud music. And also when we go to gigs and music festivals, we are exposed to very, very loud levels of noise and sound that tend to be a bit unsafe. And so if I listen to this very loud sound, that's not just something temporarily that's causing me harm. Like if I'm listening to this very loud sound, this can lead to a permanent impact?

5:16That's a very good point. It's like everything is a matter of a spectrum. If you listen to a certain level of sound for a short period of time, it may be a temporary shift. You may have a temporary sort of loss of perception, what is called your threshold sort of race, but they are reversible. But once you get to a certain critical point, then you're producing permanent damage, and then that's not reversible. And how long does it take for this permanent hearing loss to happen? It depends on the aggression. It can be immediate if you are exposed to a very loud noise, or it can take years or decades of aging for that to develop.

5:56So if I'm listening to really loud music on my headphones, like all the time for hours a day, like over what sort of time period would I expect to see an impact? That will anticipate the onset of this healing loss. But if you are exposed, for example, to an explosion, it can be loud enough that produce permanent deafness there and then. So it all depends about the impact of the aggression. I want to talk for a minute more actually about the headphones because I don't know at what level my headphone is safe and what level my headphone isn't. I've noticed that parents tend to be quite cautious now with little babies, which I never saw when I was young.

6:42But now I've noticed that sometimes you're going to some sort of concert or party with this loud music and you see like parents have put these sort of ear protectors over little babies. But I notice nobody else is wearing these protectors. How do I know at what point with my headphone this is sort of safe? It's very difficult to give general advice because it all depends very much of the device, of the particular device. Some devices come with very clear guidelines of what is safe and that you should turn your volume down. As a general rule, I would say you have to keep the level of sound to a comfortable level without getting too loud.

7:18The way that we measure sound intensity is in decibels, which is a scale, and it's basically the pressure that the sound makes, because at the end of the day, the sound is a mechanical pressure. So anything, I would say probably about 60 decibels, it will be potentially a problem. 70, 80 will be quite loud. To give you an idea, about 100 dB is for decibels, is the sound that a pneumatic drill does on the street. So we're talking about very, very loud noises when you get that and the scale is logarithmic so an increment of 10 points is 100 fold basically so just to play that back you're saying if i'm listening to music at 60 decibels that's potentially a problem and at 70 to 80 that is definitely a problem that is definitely a problem i will i will i would not recommend to go at those levels with headphones attached to phones i could be in a position where i've got more than 60 decibels in my ear it is possible and in general will be, the advice will be just put the volume down.

8:20It's really interesting hearing you talk about this because it reminds me, we talk a lot about health span on this podcast, the way in which we are on average living longer than our ancestors, but actually the number of healthy years that we're having is actually much worse now than it was 50 years ago. And I'm thinking that there's some analogy here a bit with my hearing, which is again, we're living longer, but it sounds like you're saying potentially we might have fewer years of good hearing from my grandparents? And we want to increase the lifespan of healthy years. And that has an impact, not only a personal impact, but also a socioeconomical impact.

8:57The ability to increase your healthy years is very, very important from a point of view of community as well, not only a personal point of view. What's it like to suffer hearing loss and how does it impact your life? it can have a very, very substantial impact. One of the things, and I think probably a lot of people in the audience may relate to this, you start having to put the volume up in certain devices because you cannot get the same kind of information, the same kind of hearing that you had before. But that, in a way, is more of a symptom. The thing when it starts impacting your life is when it starts affecting your communication with other people.

9:35There is a very telling sentence that Helen Keller was a teacher, suffered from blindness and hearing loss in the first part of the 20th century. And because she was blind and deaf, she was asked which one was impacting her life more, the loss of sight or the loss of hearing. And she very pognitively said, and I'm paraphrasing here, but it was without a doubt hearing, because blindness sort of cuts you off from things around you. But hearing cuts you from people because it affects communication. You go to a pub to have a conversation with some friends, and all of a sudden you are in that very loud environment, and you cannot understand what they are saying.

10:17And you start asking for them to repeat things, and after a while you just feel embarrassed. You don't want to ask the same thing over and over again. And then you start feeling more withdrawn, more ostracized, and then you stop going to the pub because I can't hear what they are saying. I can't have a conversation. And that is impacting your ability to communicate, your ability to interact, but force you to kind of almost withdraw from your social life. And that has a huge impact on your daily life and on your future sort of welfare as well, your social interaction. How does that then affect your health?

10:52One of the things that healing loss has been shown in the last few years, and there is an increasing volume of research, identifying a link between, for example, healing loss and dementia. roughly it is said for those people that develop severe healing loss in sort of midlife they have a five-fold enhanced risk of developing dementia and later on hi professor tim specter here have you heard about our documentary the gut health challenge we challenged sarah rob and lucy to transform their health in just six weeks by improving their gut health if you've ever wondered how Zoe works, this documentary reveals all.

11:34When our participants started, they struggled with everything from brain fog and sleep troubles and low energy. Can eating the Zoe way address these issues and improve their health markers in just six weeks? You'll get a behind-the-scenes look at Zoe and discover some great, actionable advice from Federica and Sarah. Follow their journey by searching Gut Health Challenge on YouTube. They have a five-fold higher risk of getting dementia if you get hearing loss. If you get severe hearing loss. If you have a moderate hearing loss, it's about two-fold the risk later in life. Why is that? It is still not clear.

12:14There are different theories trying to explain this. One is cognitive overload. You need to make more effort to listen and to understand. So your brain uses a lot more brain power, to call it in a simple way, and that sort of produces kind of a more intense sort of work there. There are other theories that perhaps the conditions that lead to develop healing loss are underpinning and underline the condition that will develop dementia as well. Whatever the explanation and the justification of the link is, it's clear that the link seems to be there. And we can minimize that risk by intervening early with your hearing loss, when you start feeling that you are losing your sense of hearing.

12:56I find it rather extraordinary that hearing loss should have such a big impact because we've done podcasts talking about dementia and people are offering talking about this thing is like a 30 % increase or a 40 % increase in risk. So it's like fivefold is enormous. It is one of the highest sort of links, but also one of the things that can be modified because other things like, for example, genetics are more difficult to impact. But hearing loss is one of those that is something that can be done in order to prevent the higher risk later in life. If I was having hearing loss, but then I had some sort of device that meant that I can hear better, does that reduce the risk of dementia?

13:37Yes. Even with the devices which are currently available, for example, the use of hearing aids, they reduce the risk because this theory of the cognitive overload, if you need to make a lot more effort to understand what people are saying and use a lot more of your brain space to follow a conversation, you reduce that. You take it back to more normal levels by using something as available as a hearing aid. So one theory is somehow my brain is doing so much work to try and understand a conversation that somehow its normal processes are being disrupted. Yeah, it's an overload that then tends to more wear and tear that then impacts.

14:15That's one of the theories. But it seems to be one of the more prevalent theories at the moment. And so therefore, if I can use some sort of device that makes it easier to understand, then my brain can continue to function in a healthier way. Well, it's definitely a very big argument, I guess, for looking after our hearing and thinking about it. I know scientists have been working on a cure for hearing loss for many decades and also really understanding what's going on in hearing. Could you maybe start at the beginning? In simple terms, how do we hear and why does it stop working? The way that we hear is in some of our heads, in what's called the temporal bone.

14:54There is an organ called the cochlea. And cochlea comes from a Greek word which basically means snail. and it has the shape of a snail, the one that you can find by the sea, for example. It's a bit of thin bone, but inside a big piece of bone, which is on the side of your head, basically. And for those just listening, you're sort of pointing to just inside your ear. Is that where we're going? Yeah, that's exactly what it is. This cochlea has a lot of important cells, but we can sort of take it to a core of like two critical cell types. One is called the hair cell, and the hair cell, which is inside the cochlea, Remember I said sound is a pressure wave, it's a movement.

15:32So it takes the sound that comes through your outer ear and then through your middle ear, the movement of those little bones that you have in the middle ear. All that pressure gets transmitted to the cochlea and the hair cell, it's called hair cell because it has something on the top that looks like hair. They're not really hairs, but that's what they look like. And they move, and that movement converts that sound into an electrical signal. That cell converts a mechanical input into an electrical signal that is then the way that signal travels in the body, sort of through the nerve system, basically.

16:12But that electrical signal, which is there in the cochlea, needs to be transmitted to the brain. So the brain can make sense that we are hearing something. And that transmission is done by a second cell in the pathway, which is called the neuron. So you have the hair cell, which is the mechanotransducer, converts sound into electricity. But then the electrical stimulus is transferred to the brain by this cell called the cochlear neuron. So the cochlear neuron is the cable that connects the hair cell with the brain. I think most people are used to this idea that a speaker is like, because you think about being at a, I don't know, like a rave or somewhere big, you can literally see it bouncing backwards and forwards when it's making these really big noises.

16:57And so I guess that is the sound pressure you're talking about. You can see it there. So you can see it. And I know that my microphone is sort of the other way around, isn't it? That when I talk at it, it's sort of bouncing around something inside this and that's turning it into electricity. Absolutely. It's a very good analogy. In my head, I have almost the same thing, only it's like little hairs bouncing around. But they are literally doing the same thing of turning the pressure in the air into electrical signals. They're very similar to anyone who's on a Zoom call or whatever, like with their computer.

17:28It's actually something quite similar in my head. Yes. The way that this machinery works is absolutely incredible. But the bottom line is precisely that. The hair cell converts this mechanical pressure wave into an electrical signal. And that's why it's the first cell in that part. But then if you have that information out there and doesn't reach your brain, then you have a problem because there is no transmission. So you need to take all that information in a very sophisticated way to the brain. And that job, the cable of your microphone, is done by the neuron that connects the hair cell with the brain.

18:08So for people who are having hearing loss, what's going wrong? We're going to concentrate only in the one affecting these cells, because you can have what is called conductive hearing loss, which affects the middle ear in those ossicles. But that is not as prevalent as what is called sensor neural hearing loss, which is the healing loss that affects the hair cells or the neurons, healing loss that affect the cochlea. So, for example, if you have very loud noises, it could affect the hair cells and then damage and destroy the hair cells. But in the last 10, 15 years, it has become more obvious and there is more information and we are more aware now how important the neurons also are.

18:58And it seems to be that we tend to lose the neurons and actually the connection between the neuron and the hair cell, we tend to lose that way before we lose the hair cells. So the loss of the neurons and the loss of the innervation that is called the connection between the neuron and the hair cell tend to happen at an early point in the process of becoming deaf. The neurons are like the cables that are plugged into my microphone, which in this case is these hair cells. And you're saying that the reason why you might lose your hearing could be like the damage to these hair cells. But actually, before you even see damage to hair cells, it's almost like these cables have been unplugged.

19:39Yes, absolutely. That is a very good analogy. And that's something which is relatively new in the field because the traditional view was that you lose the hair cells. And that is the most important thing. And then eventually, down the road with time, you start losing the neurons. But actually, it seems to be that the case is a little bit the way around. The neurons become unplugged first, and then you start losing the neurons and losing as well the hair cells. And then you lose the hair cells and you lose the neurons. And depending on which one or the other you lose is the balance. But one thing I haven't said, which is very important to understand why all this is important, is that we don't have the capacity to repair or to regenerate these cells.

20:19We as a species, sort of humans, but also mammals in general, because the ear is so sophisticated, we have lost the capacity through evolution of regenerating these cells. Some other vertebrates, for example, amphibians, will have the capacity to produce new hair cells through the life span. But mammalians in general, and humans, we are mammals, we don't have that capacity. So you are born, and this is fascinating, you are born with the cells which are meant to last your lifetime. So if you are 80, 85 years old, your hair cells and your cochlear neurons are 85 years old, as old as you are. And that's why aging is an important factor in the incidence of hearing loss, because obviously they have worked all your life.

21:11and they're starting to grow a little bit unfunctional. You've talked about how maybe a very loud noises are bad for our hearing. If I have them for my entire life, are some of them just sort of dying off, like old age of those cells over time as well? Yes. Cells will start dying off with time, and that is almost like a normal rate that we're losing them. But you can improve that rate of losing them. You can anticipate that by exposing them to loud noises, There are kind of environmental factors that can also impact, for example, certain medicines, certain antibiotics, for example, can damage your hair cells, can damage your neurons.

21:52So there are other things that will impact. But the bottleneck at the end is that because we cannot regenerate these cells, once they're gone, are gone for good. And that's why deafness is permanent. So it's very precious. It's like, I've got this fixed number. Yeah. What? But that's all I've got. You know, if I live long enough, I'm going to end up deaf, basically. One bit I don't understand yet, Marcelo, why does loud noise cause this damage? It's a very good point, and there's been quite a bit of research on that. One impact that the loud noise has is that because you are forcing the system to overreact, you are overstimulating the system, then the connection between the hair cell and the neuron become what is called cytotoxic or neurotoxic, stimulated so much, then you produce that unplugged between the neuron and the hair cell.

22:46But also, if the damage continues, if you have that continued stimulation, those hairs, those bundles on the top of the hair cell can also get physically damaged as well. So, the system can have a mechanical impact to the loud noise, but also damage by the stimulation becoming sort of quite toxic to the system. And then you have inflammation that comes after that, and that also can damage the hair cells and the neurons. So the loud noise can act in different ways, but the bottom line is that you will damage and lose your critical sensory cells and neurons. So now you've explained that they can't fix themselves and like the damage that happens, it makes me feel like I should probably take my hearing more seriously than I have done.

23:36It's a shame I'm already 50. I probably should have had this conversation with myself when I was 16. How worried should I be about, for example, going to a really loud concert for two hours? The more precautions you can have, the better. If you're going to go to a very loud concert, you can use some ear defenses, some ear plugs that will sort of attenuate the intensity of the sound. If you're listening to music in your headphones, turn the volume down a little bit. Very loud blasts can have permanent damage. And what about when I'm walking past the person digging up the road with a pneumatic drill?

24:17Because I was just thinking about that. I had that experience only last week and was thinking, wow, that is really loud. Yeah. Sometimes just protecting your ears with your fingers. Sometimes it's a very loud bang. You're completely caught by surprise and unprepared. But it's something that you can see it coming or hear it coming, then you can at least try to minimize it. Can we talk about fixing this? Sure. Because hearing aids have been around for a long time. Don't they just solve the problem for everybody? No, I'm afraid not. Let me put it this way. At the moment, there is no biological treatment for hearing loss.

24:53We have two therapies, which they do a fantastic job, but they have their time and place. These two therapies are basically prosthetic devices. One is the hearing aid. The hearing aid is pretty much an amplifier, to put it in a very simple term. So the noise that comes through your ears, it gets amplified in a very kind of intelligent way. But the bottom line is you need to have quite a bit of residual hearing in order to use hearing aids. So basically take your hearing from a level to a better level. But then you have the cochlear implant. It works in a different way. You may know somebody that has a cochlear implant.

25:35It has a speech processor or a mechanotransducer. The big difference between the hearing aids and the cochlear implant is the cochlear implant is implanted surgically because it needs to go all the way into your cochlea. So that's the bone inside my head. The bone inside your head. And it has a bit which is put outside your head, which is this mechanotransducer or speech processor, and that converts sound into an electrical signal, and then that electrical signal is transported through an electrode, through a piece of cable, piece of wire, that goes all the way into the cochlea and stimulates the nerve.

26:16so it does the job of the hair cell so the cochlear implant replaces the hair cells that's amazing so basically if i don't have any hair cells but i do still have some of these neurons that you're talking about like these cables we can now sort of put an artificial ear on the outside and a wire that goes into my brain absolutely it doesn't go into your brain it goes into the cochlear which is kind of outside the brain but you say something there which is critical, which is like if you have enough neurons. So you need to have neurons. You need to have the cable to be stimulated with the cochlear implant for the cochlear implant to work.

26:51The problem is not all the patients that have hearing loss have enough or have good quality neurons to work with the cochlear implant. Don't get me wrong. The cochlear implant does an amazing job and has done a lot of good for the deaf population. And it's really, at the moment, the best solution that we have for many of these conditions. But you need to qualify for that. You need to have a very profound level of deafness, but enough neurons to be able to work in a reasonable way. The problem is, if you don't have the neurons, you basically have no alternative, no solution. There's nothing that can help us to fix that kind of what is called neural healing loss.