We are the Association for Child and Adolescent Mental Health, or ACAMH for short, And this is ACAMH Learn. Hello, and welcome to Mind the Kids podcast series. I'm Mark Tebbs, and I'm your host for today. I've spent my whole career working in mental health, from frontline service delivery through to director of mental health commissioning. I'm now a chief exec of a charity, so I'm really interested in how grassroots organisations can improve community being. I'm also a parent and I've seen the mental health system from the other side, so I'm really delighted to be hosting these podcasts. We speak to researchers and practitioners, and it gives us an opportunity to shine a spotlight on the latest developments in child and adolescent mental health research. Today we're talking about infant sleep, something I remember all too well from when my children were small. I think I would have given almost anything for an extra couple of hours sleep at that time. I'm really pleased to be joined by Charlotte Viktorsson, the lead author of a fascinating longitudinal study exploring the genetic and environmental influences on sleep quality, settling, and sleep duration at two and five months. And this paper was published in JCPP Advances, one of ACAM's three journals. Hi, Charlotte. Lovely to be speaking to you. Do you want to just give us a little bit of an introduction about yourself, maybe where you're working, your research interests, and it's a nice opportunity to give a name check to the people that you worked with on the study. Yeah, sure. I'm Dr. Charlotte Viktorsson, and I'm a researcher in the development and neurodiversity lab at Uppsala University. And my main research interests are within behavioural genetics, so examining genetic and environmental influences on behaviours in early infancy and childhood. And on this paper, we in the Dive Lab work together with researchers from Karolinska Institutet, but also a researcher from University of Surrey. And the PI of this study was Professor Falck-Ytter from the Dive Lab. Thank you. So let's just start by trying to set the scene. So it'd be great if you could just give us an overview of the study and what were you setting out to explore. Yeah, sure. In this study, we wanted to examine genetic and environmental influence on early sleep and settle behaviours. So more specifically, we measured how many times per night the infants woke up, how long it took for them to settle when it was time to sleep, and also the crying duration each day. And this was in two and five-month-old infants. And it was a questionnaire-based study, which was sent out to families all over Sweden. And in the end, almost 1,000 twins participated in the study. I remember that period of time so well. That early infant, and you're desperation for some sleep. So I'm sure a lot of people will be really intrigued by your findings. It'd be good to just understand a little bit more about why sleep in infancy is so important. Sleep is very important. It is important in infancy. It's also important later on in development, of course. Throughout life, it's very important with sleep. And also crying is important, of course, in terms of stress for the parents, how much of a toll it takes on them to have an infant that cries excessively. While sleep is important more in terms of learning, for example, and development in that sense, it's also an area-- they're both interesting in terms of research, just understanding infant development, but it's also an area that is very interesting in terms of being able to help parents cope with this time in their baby's life and with the stress that might come with it. Yeah, I remember there being lots of advice at that period of time, but none of it feeling like it was particularly helpful. [LAUGHS] So could you tell us a little bit about what's the existing research telling us, and what gap were you trying to fill with your study? So we knew that later on in childhood or in toddlerhood basically, [INAUDIBLE] seems to be heritable. So there was some genetic influence on crying it has been found. Also, some parts of sleep, such as sleep duration, do have some genetic influence later on in infancy. But there was a pretty big gap, I would say, when it comes to the first months of life in an infant's life. We wanted to study these behaviours very early on. And that is not only in terms of just understanding development, because we cannot ignore the first months of life. We know that there are so many changes happening during these first months. But also in terms of as I said, the parent perspective. These first months can be very tiresome. and you can have a children that doesn't sleep well, that cries excessively during these first months. And that's why we wanted to focus on this very early period. So how did you go about this study? So it's a longitudinal twin study. So you could maybe explain what that is and why you chose that methodology to study this area. Yeah. We studied the same twins at both two and five months of age. And that is partly because we wanted to see how these behaviours developed over time during the first few months. But longitudinal twin study also allows us to examine whether the same influences are active both at two and five months. So that could tell us whether, for example, the same genetic influences are at two months as at five months. So it gives us more information than just looking at these behaviours at two separate time points in two separate samples. And you mentioned it was like a questionnaire study, I think, that was your phrase. So how did you go about measuring sleep quality, and settling behaviours, and crying duration? These questions are from a questionnaire called the Sleep and Settle questionnaire, which is mostly used for infants and perhaps older toddlers as well. It's a parent-rated questionnaire that we sent out online, partly because this is part of a much larger study where we have collected data on temperament, and language, and many other traits. We asked parents to rate these behaviours as an average for the last week, basically. And so was there any particular challenges in terms of that kind of methodology and collection of data? Of course, there is always some bias when you have a parent report, but on the other hand, we believe that parents actually know their children very well. Using questionnaires allowed us to include families from all over Sweden, which also makes our sample more representative of the Swedish population. And while we were a bit worried in the beginning that maybe twins don't sleep in the same way as singletons. Singletons is children who do not have a twin. Maybe they will wake up more frequently, or maybe they cry more because, well, there are two babies and that means more work for the parents. We actually published a study before this one where we compared twins and singletons, and we found that there weren't any significant differences when it comes to crying duration, or how long it takes for them to settle. There was a slight difference in wakeups during the night, but actually, the twins woke up less according to that study. So we do not believe that there were any large issues with the measurement, but of course, you always have to keep in mind that it is parent-rated questionnaires and not a lab-based study. Before we go into the findings, I think it might be really useful just to explain genetic and non-shared environmental factors. So before you go into the results, it'd be really useful just to explain some of the terms that you're going to use in that description of your findings. I can just shortly explain a twin study. And that is we include both monozygotic and dizygotic twins. Monozygotic twins are identical genetically, while dizygotic twins share approximately 50% of their genes, and that is just as any other siblings. And what we do is that we look at how similar are the two twins in a pair to each other. And if monozygotic twins are more similar to each other than the dizygotic twins are when it comes to, for example, crying, then that suggests that we have genetic influence on this trait. So genetic influence on a certain trait means that if we see differences between individuals in a population, then those differences are largely due to genetic differences between these individuals. While shared environment means any environment that the infants share. It could be parental practises or in which room they sleep, for example, could be socioeconomic status or something like that, while non-shared environment is unique environment to that twin. At this age, it could be, for example, an illness that has only affected one twin, and later in life, it could be that twin specific friends or a specific hobby that twin is doing. OK, so let's turn to the findings then. So what were the key findings from the study? I think the most interesting finding was that crying duration was largely influenced by genetics at both two and five months. So differences between individuals largely due to genetic differences. And I just want to clarify that doesn't mean that parents are not important, because of course, they are very important. It's very important to comfort your child. It's very important to create a stable and loving environment. But what it does mean is that there might be two families that are equally loving, and stable and comforting, but where the child in one family cries a lot more than the child in the other family, and that difference is largely due to genetics. So it means that after you've met the child's basic needs and you've given them love and comfort, there's honestly not much more you can do. And some children will simply cry a lot more than others. I think that's quite a comforting message, actually, [LAUGHS] because I think sometimes as a parent, you think it's all your fault. And actually to hear that, even with your best efforts, there's a genetic component, I think, there's some comfort there. I hope it will be at least somewhat comforting for parents to know this. When it comes to sleep, instead, we found more of an influence from shared environment. So that could be, for example, parental practises. But this type of study cannot really tell us what those factors are in the environment so we need to do more research to find that out. OK. All right, yeah. And is that what you expected to find? Was it a different finding to what your initial expectations were? It was a surprisingly high genetic influence on crying, I would say. I didn't expect it to be that high, but we did expect to find genetic influence. So in that sense, it was in the expected direction. And no one has ever looked at in these first months of life so we didn't really know what the level of genetic influence. So in that sense, it was in the direction you would expect based on earlier studies. How are you interpreting the patterns that you've seen in this study? Well, for the genetic influence on crying, that could be due to, for example, temperamental differences, which we know are quite heritable. Of course, it could also be some heritable issues when it comes to infants often have gastrointestinal issues that makes them cry a lot. It could be something related to that. We don't know based on this data. When it comes to sleep, that suggests that parental practises may have quite a large influence, and that is also what we expected from earlier research. So it suggests that if we want to help the infant sleep better and settle better, we should probably be focusing on the parental practises surrounding sleep. And when it comes to crying, well, yeah, there's not much more we can do. Were there any kind of differences-- I'm just thinking about the kind of cohort you studied. So obviously it's was based in Sweden. So were there any particularities of the cohorts that were interesting to share? We didn't look at any group differences within this cohort. One reason, is that to do twin studies, we need very large samples. And while 1,000 twins might sound like a very large sample, it is not within a twin-modelling research area. We weren't able to look at differences in influences across any groups within this cohort, unfortunately. So I'm just thinking about the broader implications of this, and you've kind of touched a little bit. What might your findings mean for early parenting, particularly routines or soothing techniques? Well, I hope, as I mentioned, that it might be somewhat comforting for parents to know that it's not their fault that their child is crying, and perhaps it might relieve some stress for parents with children who cry excessively. When it comes to sleep, I think based on this study, I cannot give any recommendations for what to do to make your child sleep better, but it does suggest that we need to research this further to find out what factors may influence sleep at this very early age. And based on that, perhaps we can make some recommendations for parents. So more research in the area. I think the underlying message around there being a big genetic component, I feel that in itself is a really important finding. I think if I'd heard that when I was going through those kind of difficult, sleepless nights with my own children, it would have-- I think I would have felt a lot of reassurance through that. So many parents feel pressure when their baby is struggling to sleep or cry. Could you tell us what the research says to help them understand what's within and outside of their control? Well, it's basically what I've already mentioned, that of course, you need to comfort them, and you need to provide a stable environment. Babies like routines, that makes them settle better. So creating that kind of stable and loving environment when it comes to crying, that is basically the advice that I would give at this point. And then excessive crying outside of that-- I mean, of course, if you would suspect that there is something wrong, that the infant is in pain or anything, of course, you need to seek medical advice regarding that. But otherwise, if you know that the infant is fine, not much more we can do at that point. So you've touched on this a little bit, but what are the key questions that still need answering in this research area? Well partly, as I mentioned, it's what factors influences sleep at this early age. Like what can parents actually do? We need to find out more about that. But also I think looking at these behaviours both early on as we have done, but also later on in development. So looking at these behaviours developmentally across the first years of life would be very beneficial to examine do we see the same pattern across development, or are there certain time points where maybe the parents' influence is larger than at other time points? Maybe that is when we should try to influence the infant's sleep more than other time points. That would be my suggestion. And have you got further research lined up there? Have you got other studies planned? Well, actually, for this specific sample, we have followed them from two months of age to three years of age. So actually, our next goal is to analyse the data that we have. This has already been collected all of it. And so not only looking at these behaviours in the first months of life, but actually in the first years of life and see whether we find the same patterns or maybe something changes across development. We don't know yet, but it will be very exciting to find out. Great stuff. OK, so we're coming to the end of the podcast. Is there a final take-home message for the listeners? Well, that would be that it's not your fault if your infant is crying a lot. You're doing great. And well, yeah, that would be it maybe. [LAUGHS] Great stuff, Charlotte. It's been lovely speaking to you. Thank you for your time today. For our listeners, if you've enjoyed our podcast, then please leave us a review or a rating on your platform. And thanks for listening. [AUDIO LOGO]