We are the Association for Child and Adolescent Mental Health, or ACAMH for short. And this is ACAMH LEARN. Welcome to "Mind the Kids." I'm Dr. Jane Gilmour, Honorary Consultant, Clinical Psychologist, and Child Development Programme Director at UCL. And I'm Umar Taceeb, Professor of Psychology at the University of York, focusing on children and young people's mental health and special educational needs. In each episode, we select a topic from the research literature and, in conversation with invited authors, sift through the data, dilemmas, and debates to leave you with our takeaways for academics and practitioners. Today, we'll be discussing fatigue and its relationship with depression in young people. This episode is called Depression symptoms, should fatigue be in the major league? And fatigue. So this is an interesting one because before I read any of the work of our guests today, I would have used fatigue interchangeably with tiredness, exhaustion, lack of energy, et cetera, et cetera. And those words do describe what fatigue is. But actually, within the context of mental health, it's a symptom of clinical depression or major depressive disorder. And I think one of the key things that I took away when I was reading about this was, no amount of sleep is going to help with fatigue. It's not tiredness that can be helped by just sleeping more. There's something different about this. Sorry, go on, Jane. No, I was just going to say, because I think there was-- I think the differentiation is really interesting and very important, and it was something that-- and we'll talk to Nina about this as we go into her paper in further detail. The idea of that qualitative data that's included where young people were asked to describe tiredness and fatigue, and it was seen as a continuum of severity, not differentiated in terms of categories. Fatigue was at the most extreme end of their tiredness continuum, if you like, which I thought was really interesting. Although as you say in the literature, certainly, fatigue is seen as more complex, more multi-dimensional in terms of its underlying causes, physical, mental perhaps a biopsychosocial model. But that differentiation is really important when we're thinking about how we consider it as part of a low mood, collection of features or symptoms. And I find fatigue an interesting symptom because, again, not in any sort of academic way, but as this random human being. [LAUGHS] I think of fatigue, and maybe this is my misconception here, I've associated with much more of it being a symptom of a physical illness, like a physical-- and then because of that, intuitively, I'm like, oh, yeah, so maybe there's a physical cause for this. Is there something in my diet or iron or something like that? And that's very different for the kind of work that I do, just because I'm on the TV show at the moment in Educating Yorkshire. In one of the earlier episodes, I think there was a teacher who attributed a child's behaviour to their diet. And actually, I think they had ADHD. And then on X or Twitter, some people were like, oh god, not the teacher attributing this person's ADHD to diet. So in those kinds of neurodevelopmental conditions, to attribute something to diet might be seen as problematic. But actually here, maybe there is some aspect of diet here. I don't know, and we're going to get into that. But we know if we think about the symptoms of depression, one of them can be a lack of appetite or an increased appetite. And if we think about the conversation that we had with Ian a few weeks ago where we think about symptoms reinforcing each other, one leading to another or one causing another, there might well be a link there. Yeah, I was just going to say that-- so just for those listeners that haven't heard all the episodes, that Ian Goodyear episode is the reboot of the great psychotherapy debate, and it is a relevant episode because it really links really nicely to this current episode as well. And I think I just want to contextualise fatigue within major depressive disorder or depression. Before you do that, Umar, because I want to come back to the idea of definition, because I think this is really important. Because although the literature talks about the idea of this multifactorial underpinning to fatigue, whereas tiredness is much more of a symptom in its true sense, a sort of subjective description, if young people, or indeed somebody of any age, are considering fatigue at the extreme end of tiredness, and we are relying on self-report and symptom description, it's actually quite important to know if we should consider them categories or if for those young people it is something similar but a more extreme version of tiredness, because that will change the way they report it and the way they experience it. So I think it is a good topic to explore in a little bit more detail. I'm not suggesting I have the answer, but I do think it's important that we recognise those self report features will depend very much on the young person's construct of what they're answering. But I interrupted you. Let's look at those features of depression, because I think this is probably one of your favourite subjects, constructing [LAUGHS] [INAUDIBLE] --the diagnostic classification. Never happier, Umar. Go for it. It seems that when we think about-- well, not it seems. When we think about the diagnostic criteria for major depressive disorder, you have your core symptoms. So that's either depressed mood or loss of interest or pleasure, or both, and then you have a combination of four or more of nine other symptoms. And one of those can be fatigue. But it's perfectly possible to have major depressive disorder without having any symptom of-- you can have every other combination that doesn't include fatigue and still get a diagnosis for depression. And that's just another example, like you say, of my view that these diagnostic labels are flawed. Because if we have a young person who has depression and one of the symptoms-- so let's just say depressed mood with lots of symptoms, including fatigue, that's a very different condition to a loss of interest and pleasure in the activities that they usually enjoy, and a different set of combination of symptoms without fatigue. But they would both be major depressive disorder or they would both be considered depression. But I just wanted to just put that out there just because any opportunity to drag down the system [INAUDIBLE] [LAUGHTER] --also just to contextualise fatigue within the diagnostic criteria. And maybe those-- much like there's a debate in autism, and there is inevitably in this debate in the literature about coming to the same diagnosis from a variety of different routes and causes, so perhaps there's something in that. But it is interesting of that gathering momentum, looking at fatigue as a core symptom, and that the current classification system doesn't require it. I think it's very interesting, and I knew it would make you happy when we thought about that, yeah. So we bring in our guests. Yes, I think we should, because we've got lots of questions. And I think our guest is in a perfect position to help us figure out what's going on here. So today, we're joined by Dr. Nina Higson-Sweeney from the University of Oxford. Nina's PhD thesis focused on fatigue in adolescents with depression. Welcome, Nina. Hi. Thank you so much for having me. Oh, thank you for agreeing to come on this podcast. And thank you-- before we even get to it, I am loving this-- you have this yay energy. This is going to be a really fun podcast. I know that it's not going to be like-- it never is boring. But it's going to be even more energetic than it usually is. Oh, I've got a lot to live up to. So let's start with, Jane and I have been talking about fatigue and our understanding of fatigue. But we're not the experts on fatigue. You are. But what is fatigue, and what is the definition that you've been working with that we should bear in mind when we're going through this podcast so we have a reference point? Yeah, it's a good question. And I think throughout my PhD, it's not one that I ever came to a super firm answer to. So I mean, people talk about fatigue in many different ways-- lack of energy, exhaustion, feeling drained. And there's generally a lack of consensus about how to define it. People define it in different ways. So, for example, there are quite a few debates about, OK, what is pathological or nonpathological fatigue? So this idea that there's a normal kind of fatigue and an abnormal fatigue. Some people categorise it that way. So a nonpathological or a normal fatigue would be quite a protective reaction in the body to low energy levels. And it can happen day to day. It quickly happens, so you'll quickly feel this fatigue after these activities, for example. And it's quite quick and easy to resolve it. So you have a nap, or you need to rest and eat and restore that energy. That would be that normal fatigue. Whereas a pathological or abnormal fatigue might be longer in duration, not necessarily linked to this use of energy, as we'd recognise it. Usually a lot more severe, and often part of a broader illness. But again, that's just some way of differentiating between the two. It's not necessarily agreed upon. And I think for me, I was really conscious of that fact when approaching my PhD. And like, OK, what is fatigue? And so I tend to define it as a subjective state of extreme mental and/or physical exhaustion following normal activities. So this idea that it has different components. It can affect you in different ways. It's really subjective. It's really experienced differently by different people. And it is this idea that the kind of fatigue I'm looking at, it's not that day to day tiredness when maybe you've been at school, you've been working for most of the day, you've had travel, you've had activities, and then you're feeling really, really tired and ready for bed. It's not that kind of fatigue we're talking about. It's this, I don't know why I'm feeling so drained when I haven't necessarily done something to cause that. So it's subjective, which is really important when we're coming to think about self-report and so on. And it's disproportionate to the activity or the challenge that's been in front of that young person. That's really helpful. It's very tidily conceptualised. You've spent three years thinking about this, and I might imagine that that's the case. But that's very helpful, I think, when one's looking at the literature, because I think there isn't consensus, it is quite muddled. Could you explain a little bit about how you got to explore fatigue? What brought you to focus on this topic? And it seems that there is a gathering momentum to look at this, so we're really interested to find out about your processes of how you got to the topic. Yeah. Well, it's a little bit of everything, really. So one hand, I've had personal experiences of fatigue. Though, mine was actually linked to a physical illness, so hypothyroidism. So that's an underactive thyroid. And fatigue is one of those main symptoms. But I'd had that experience of this real fog, this real need to nap. But you're not really doing anything, and it's very confusing. And it can completely impact your day to day. So I think generally, fatigue-- we call fatigue a transdiagnostic symptom. And by that, we mean it can feature in so many different illnesses. So depression is one of them, but hypothyroidism is another. Sometimes it's an anxiety, for example. So yeah, I already had a personal interest in it knowing how debilitating it could be. Luckily, mine had a fix. And then also, when I was doing my undergraduate degree-- so I studied psychology at Uni Bristol. I did a placement year as a research assistant with Dr. Maria Loades, who ended up being my PhD supervisor. And she is a clinical psychologist, and she was doing her PhD at the time. And she was looking at depression in young people with chronic fatigue syndrome or ME. So looking at a slightly different angle, but that intertwined between symptoms of depression and this illness where fatigue is such a core issue. So I did a lot of work on that. That was really when I was getting into research. So it made sense to look at it from a slightly different angle. At the time as well, you started to have other PhD students and other researchers looking more at individual symptoms of depression to understand more about the structure of it, more about how it works. And Rebecca Watson, who was at Reading at the time, she did her PhD on anhedonia in adolescent depression. So really fascinating work, a lot of qualitative research that did mention fatigue in the context of depression, in the context of anhedonia, which is when we talk about that loss of interest and pleasure. That's what we mean. And so, yeah, I was quite influenced to do a deep dive on fatigue as well. I just want to pick up on something that you said then, just to make sure I've understood it correctly. So part of your description of fatigue was-- you didn't use these words, but a difficulty in initiating something that you want to do. And if a young person experiences that, how do you distinguish between that and procrastination? As in, like, that's also a difficulty to initiate something. So how do you separate that from fatigue? How do you know you can't do something because you're fatigued versus you can't do something because you can't find the motivation to do it, which I think is what procrastination is? Yeah. And this is the thing, because obviously, your motivation comes up a lot with depression as well, and they're all interlinked. And I think that's what I'll keep coming back to that all interlinked. I think realistically, fatigue and procrastination, for example, have different underlying drives, maybe. Procrastination, for example, I know is linked a lot with perfectionism and this coping mechanism to deal with this real issue, I guess, with-- not an issue with self-concept necessarily, but this underlying issue of, I need to be hitting these targets. I need to be hitting these goals, and I'm not quite reaching it potentially, or I am, but I'm still not good enough. It's really linked with your self-esteem and stuff. Procrastination can be this coping mechanism to potentially avoid-- And it might also-- --tasks, and then need to. Yeah. Apologies, needed to interrupt. But it also might be just a frank, executive dysfunction as well, which could be manifested in all sorts of ways in the typical population. But it might be as part of ADHD, for example, and so on and so on. And I think it's really interesting to pull apart the manifest behaviour might look the same, the underlying root is very different. So it's really, really useful. Yeah. I think you put that really well. I think there can be overlap for sure, but I think actually what's driving it is quite different. And I think that's why it is important to better understand fatigue, but also things like procrastination, for example, so we can understand what's driving that and then tackle that root cause. You did a really good job earlier about distinguishing between fatigue in general and then pathological fatigue when it becomes a problem for functioning. So what proportion of all children and young people would experience pathological fatigue, or what proportion of children and young people who have a diagnosis for depression have fatigue as part of that? Yeah. So I'm going to do a disclaimer in that something I found really interesting in my PhD is, I do feel like we went through a wave of research where fatigue was a hot topic. And that seemed to be in the 2000s. So there was a lot more research then, a lot more looking at prevalence and things like that. And then it died down. And then I think it's rising again with COVID, and long COVID, and we're seeing more symptoms. So I think it's coming back. So what I would say is when we're looking at how common it is, I think we need much more data, to be honest, much more up to date data and more rigorous data. But from what we see in the literature, potentially as many as 35%, 38% of adolescents might describe themselves as experiencing fatigue. Not necessarily a pathological or problematic fatigue, but just experiencing it. Whereas some people report that more problematic fatigue maybe 3% of adolescents. Well, when you think of something like that, that's like 3 in a 100 adolescents experiencing this really intensive fatigue that is not easily resolved, which is actually quite a lot. I mean, just to put in here, I think if we think about the prevalence of autism, which is somewhere between, I think, 1% and 3%, and we hear a lot about autism-- maybe it's just because we're in this field. But even out there in the nonacademic world, we hear a lot about autism. So if 3% of the children and young people are experiencing clinical levels of fatigue, then that might be on par with the level of the autistic population. It could be. And, I mean, I don't know how much research there is out there, but I think there's some really interesting ideas around, for example, masking and fatigue and things like that. I think it's another area of exploration, for sure. And it's noticeable, of course, you're talking about adolescents. So I wondered about the developmental stage. Is it significant? Because, of course, we know that during adolescence, teenagers feel emotions more intensely than they ever have before. So whether that's anxiety or euphoria. I wonder what your views are in terms of the significance of the developmental stage. Is it to do with a physical development, a hormonal stage, or an experiential stage of experiencing highs and lows at the extremes? Yeah. And I'm going to quickly go back to Umar's question about the prevalence in depression. And I think something really interesting is that in depression, we see quite high levels of adults reporting fatigue and depression and adolescents reporting fatigue in depression. So just to answer the question, I think in depression, again, varying amounts, but some reports say that 40% of depressed adolescents might report fatigue, and that could go all the way up to, one study found 97%. In my own research, which is in the study that Ian Goodyear did, there was 73% of their sample at the beginning reported fatigue. But we do see it quite commonly reported in adults and adolescents. But I do think there's something really interesting about the adolescent developmental stage, because we know that adolescence, obviously, is categorised by a lot of physical changes, psychological changes, a lot of changes in social demands. You're thinking about friendships, and school settings, and identity, and fitting in. Adolescents have so much going on. And we also know that there's differences in adolescent sleep cycles. And that idea of they struggle to go to sleep early and wake up early. We know this. And we know that that doesn't necessarily correspond with school timetables. So I think to some degree, an amount of tiredness and fatigue is quite normal for this developmental stage. But I do think there are just so many different things going on that it can actually make fatigue quite problematic. And I do wonder if that's potentially why fatigue is maybe been overlooked in this group of people, because they've got so much going on. They've got so many changes. Of course, they're going to be tired. Yeah. The only thing constant is change, as they say. And I think that when there's that degree of complexity, it confounds so many questions and so many hypotheses. So I think it's an interesting idea. And I agree with that caution about how we might consider adolescence because of those social demands in particular. Fatigue does include that social load, and I think that's a really important point to make. And it's a point well made. You talked a little bit about the talking therapies, and I know that Umar is interested in this as well. Could you just very briefly, for those perhaps new to them, describe what those therapies are before Umar gets stuck into his thoughts about that area? Yeah. So, I mean, I did quite a bit of my PhD was looking at different treatments for fatigue, but one of the studies I looked at was, I used data from this really large trial in depressed adolescents, and they received one of three talking therapies. So they either received cognitive behavioural therapy, so a real focus on identifying maladaptive cognitions and behaviours and changing that. They also did short-term psychoanalytic psychotherapy, so a lot more based on helping young people to understand themselves, what they're going through and what's happening around them. And then there was also a brief psychosocial intervention, and that was much more about psychoeducation like, what is depression? What am I experiencing? As well as some therapeutic strategies. So in the data, I looked at, these young people were randomised to one of these three talking therapies. OK, so you've got some adolescents who are in a large cohort who are experiencing depression, and they either receive one of these three interventions or no intervention at all. And what you were interested in was looking at the impact of these three types of intervention or talking therapy on fatigue specifically. Yeah, go on. I was just going to say, yeah, it was just those three. So there wasn't like a wait list. Oh, OK. Sorry. Yeah. They used the brief psychosocial intervention as the control, I guess, because it was just educational and information giving. Yeah. Yeah, I'm sorry. Yeah. So you have three types of talking therapy, and you're comparing the three to each other. And you're interested in fatigue and the impact of those three types of intervention on fatigue. What did you find? Yeah. So I was interested in looking at this data for many different reasons. It's quite high-quality data, which we always love. And yeah, so I was looking at prevalence. So like I said, about 73% of the sample did experience fatigue. At the beginning. I looked at related characteristics. So we found that those who reported quite high levels of fatigue were often older and, as might be expected, report higher depression severity overall. And then in relation to these three different treatments, we found that fatigue did seem to reduce with all three. And there wasn't much differentiation between the three. And I guess in some ways, that was expected because in the trial, which was looking at depression overall, they found that all three treatments were relative to each other. Depression reduced with all three. But I guess because of the literature, because of the impact the fatigue could have, I had questions as to whether fatigue would also reduce. And these treatments aren't what I would call fatigue-specific. And by fatigue specific, I mean a treatment that has been designed to target fatigue. It's kind of, yeah, they're designed to target depression more generally. And we did find that fatigue reduced. And we found it reduced from to the start before they received treatment to the end of treatment, and 86 weeks, so after they had finished treatment. Which suggests that these effects, this reduction of fatigue was maintained, even when they weren't experiencing those active therapies. And I think this links very nicely to when we had the conversation with Ian Goodyear previously on this podcast, because I think that was a different set of analysis with the same study and same file data. And again, there, he was trying to understand the mechanisms through which these different talking therapies work. And I think what you've done here is slightly different, but also very interesting. Because when we look at interventions, wherever they might look like, we're interested in the average, on average, are the symptoms decreasing as a result of the intervention? But then what we don't always know is whether the specific symptoms that are being impacted on what they are. And you've done that here. So you're specifically interested in fatigue, and you're interested in whether that specific symptom is being reduced as a result of these talking therapies. Sorry. I was just going to ask, Nina, do you have any sense of how, let's say, a specific fatigue therapy, so one that would be has an evidence base for, let's say, chronic fatigue syndrome, thinking about paced activity and so on and thinking about all the areas of activity that might contribute to fatigue and dropping down physical activity and so on, do you have any way of hypothesising how that would have an impact on low mood, if you see what I mean? So if we turned it the other way around and said, let's focus on fatigue specifically, what impact might it have on mood? That might be too hard a question, but just as you're talking about it, it would be a very interesting head to head. Yeah. I mean, you're getting me to recall my PhD thesis now. [LAUGHS] Yeah, I did another study. I did a systematic review, and we looked at fatigue. So not specific to depression. But one thing I looked at for my thesis and commented on my thesis was whether they'd measured depression as a secondary. So they often measured decreases in fatigue. There were no samples specifically with depressed adolescents, but sometimes depression was measured. And I had a look. I'm not 100% on this, but I'm pretty sure that we did see some reduction. So a fatigue-specific treatment, there were reductions in fatigue. But as a secondary symptom, there were also reductions in depression. I don't think it all-- it wasn't all of them. It was a very small sample, like maybe four studies or something that looked at it. Again, a secondary symptom, so there wasn't necessarily enough power in those studies to be able to detect these effects. But what I will say is I think from the research, there are hints that fatigue-specific treatments could also help with depression. And I feel like that's a stretch of what Ian's study said. But I guess Ian's study is looking at fatigue in that whether fatigue links to these other symptoms and depression as a whole and changes in fatigue, how that relates to changes in depression. That's a very roundabout answer. That's so interesting. That's fascinating. And I know that some of your other work has looked at young people's experiences of fatigue, so you spoke to young people about their experiences of fatigue. What does it feel like for children and young people who experience fatigue? Yeah. I mean, I have to say, I do feel like this study that I did for my PhD was my favourite. It was really great to talk to young people about fatigue. And actually, one thing I will say, I was blown away by how so many of my participants were like, we so struggle with this. No one talks about it. They were really actually enthused by the chance to talk about their fatigue and get their point across, and that really struck me. But yeah, I mean, it was so interesting. They'd given so much thought to how fatigue was. And I guess because it is a part of their day to day life, so yeah, they understood that fatigue was quite dynamic. So one day, they might be OK, fatigue might not be impacting them too much. Another day, really struggling to get out of bed. So it's not necessarily consistent, although it also can be so. And they did see it as this really extreme version of tiredness. They differentiated between the two. And they also, unprompted, which was quite interesting, they talked about this mental component and this physical component. And it's really interesting because that is debated in the literature. But in my interviews, I didn't use that phrasing at all. It was young people used that. So this idea that fatigue can be very physical. You feel it in your bones. But that kind of fatigue being a bit more a bit easier to identify, easier to fix, and this mental fatigue being more linked to depression, quite hard to identify, quite easy to confuse with the physical fatigue. And so I think fatigue is experienced as quite all encompassing. It's a bit all over the place, and quite hard to really make sense of. And I think another thing, thinking of the all encompassing side of things, it felt like fatigue impacted everything. So many things could make fatigue worse. Fatigue could make so much else worse in turn. It could exacerbate other depressive symptoms, this like domino effect. And yeah, I was really blown away by the severe impact it could have on young people. So this idea that they have all these day to day activities, school, family, friends, hobbies. And actually fatigue really reducing their energy, so reducing what they can do. And this idea they had a compromise on what they could engage in. So, OK, maybe they're doing their homework. They're getting their homework in time. They can't take part in after school activities because they're wiped out. So this real distinction between, here is what my friend, who doesn't have depression, who doesn't have fatigue, can do. Here is what I can do. And it really led to this sense of missing out and this guilt for not being involved, and we know how important the social elements are in that age range. So I was really struck by just the breadth of impact and the real emotional impact. Yeah. And then the final part was really they were talking a lot about how they understood fatigue and often blamed themselves for it. So feeling like they should push through it. If they were strong enough, if they were dedicated enough, they should be able to just get over it. And this was then reinforced, I suppose, by family members or friends not quite understanding why they were fatigued, because it was nothing physical. And so they were like, well, you're just being lazy. Why are you doing that. And that really giving young people the sense of, OK, it's not serious, and I can't go to a health care professional to talk about it because they're seeing all these different cases, and I'm coming to them because I'm lazy. So young people were really reluctant to seek help for it, despite the fact that they had just told me about the massive impact it was having on them. Yeah, that's a summary. It was really interesting, yeah. But how interestingly, the qualitative data from the young people put fatigue front and centre in terms of what was impacting on their functioning. And in Goodyear's data, preliminary though, it suggest at some theoretical level that fatigue might be one of the first domino in the fall of dominos in terms of depression and low moods. It's intriguing that these two data sets are arriving at somewhat similar stories. You describe that really in such an evocative way about how young people are experiencing that. And I think that underlines the importance of fatigue really nicely. And I was just going to say, and also, I think it highlights how important it is to do different kinds of research on it. We need to piece together all this different information. And I guess I'm quite relieved, almost, that we're starting to see that in fatigue, we're starting to see-- Validation. --it being focused on. Yes, yeah. [INAUDIBLE] Yeah. I've got an eye on the time, but I wonder if we should wrap up at that point? Yeah, I think it's a good point to wrap up. Because there are other questions, but I don't think they can be answered in the next five or 10 minutes before because I think we'll be here all afternoon. [LAUGHS] We could be, yeah. Yeah. So let's call it a day then. So thank you so much, Nina. That's been really, really good and really interesting, and it's given us lots to think about. And hopefully, our listeners have taken a lot from that and will be thinking about this too. So thank you. Yeah. No, thank you so much. If anyone's interested, very welcome to get in touch with me. There's a little infographic I made from my PhD research that's freely available, so I can share that with anyone who's interested. Thank you. Thank you. Thank you. What did you think, Jane. So there was-- I'm intrigued by fatigue. I have to say that I really enjoyed the way that Nina's qualitative data really adds some texture to some of the quantitative data, which is the best experience of mixed methodology, isn't it? And it really does highlight, in a tantalising way, that perhaps we should be paying more attention to fatigue and assessment. And this is something certainly-- I mean, I wouldn't say that this is my routine clinical practise, but now it will be. And I think it's worth thinking, if you are thinking clinically, that there are ways of looking at fatigue. Obviously, you can include it in your clinical assessment, but there's items-- so for example, and I think Nina described these in her paper too, the Kiddie SADS, so Kiddie Schedule for Affective Disorders and Schizophrenia, which screens a whole range of disorders and that has an item that includes fatigue. And also in the mood and feelings questionnaire, which is a self-report. So in other words, in our screens and in our general assessment, we can look at assessment. And I think I argue that we should. What about you? I think one of the things that I was reflecting on when Nina was talking, and I don't think Nina would have been able to give us an answer to this, but I think this is a research question that somebody needs to address, which is why I don't think she would have an answer. Not because I don't think she knows. She would have known if it was out there, but it's not out there, which is, I'm thinking about what we spoke to Ian about Ian Goodyear, and now that we've spoken to Nina. So various therapies might lead to a reduction in fatigue. Now, why might that be? So one explanation might be because these therapies are leading to a reduction in depression. And depression is the underlying thing that's causing fatigue. So if we can reduce the depression, then we can reduce the fatigue. The other explanation might be that these various therapies are directly impacting upon one or more symptoms of depression, which, based on Ian's work that Ian talked about, is part of a network of symptoms. So when you start to deactivate and reduce one or two or three of those symptoms, they then have a-- I think it was described as a domino effect, but in the reverse where they start to reduce other symptoms. So that might be why fatigue is being reduced. So I would be interested in seeing some work where we try and compare those competing explanations for why talking therapies would reduce fatigue. Is it because talking therapies target depression, which then reduces fatigue, or is it because talking therapies target various symptoms of depression, which might be fatigue, which then reduce fatigue? And we don't know the answer. But it would be nice if someone could do that study and find out the answer. But I'm not quite sure how you would do it, but the data set is there. I just don't know of the statistical methods that would be used to do that. But there are hints, weren't there? And I think you're right that it's a complex but necessary study. But Nina's suggestion that there were hints in the literature, and she quite rightly went no further than that. Is that if we address using from first principles our fatigue treatment package, there can be an impact on depression, which does suggest there's some-- I mean, it does suggest that there's something in there that needs to be pulled apart. Hints, but no further. It's very intriguing, I have to say. And the fact that these young people were talking about it as the thing that impacts our functioning over and above anything else was also important. I do also think, although it is conceptually in the literature, at least separate from tiredness, I think they're also-- if we're thinking about fatigue in our clinical population, we need to exclude tiredness as a contributor, particularly if these young people are seeing it as the extremity of tiredness and look at sleep hygiene and do our usual exploration improved-- and look at how improving sleep might impact on fatigue, and that may impact on their depression features as well. What's your take home takeaway? I don't know. I think that was my take home takeaway. [INAUDIBLE] What? --someone doing a study which compares is why talking therapies improve fatigue and comparing those competing explanations, because I'd like to know the answer to that. But I don't think we do know the answer to that. And I think my takeaway, maybe it's repetitive too, but I think that given the gathering data from the impact study and elsewhere. We need to have a debate about classification. Yes, we do. Umar, yes, we do, and reconsider fatigue as a key feature of low mood. Well, we really hope you enjoyed this episode, and don't forget to check out the episode at the beginning of this series where we talk to Ian Goodyear about the same data set, but a different set of analysis and a different set of research questions that will really help you to contextualise some of the things that we've talked about today. Join us again next week when we'll be speaking to Dr. Shelby Stewart about medicinal cannabis and the impact on children and young people's development. [MUSIC PLAYING]