Summary: A pioneering public health study has delivered a comprehensive, multi-disciplinary mapping of the complex crises surrounding sleep deprivation, anxiety, and depression among young adults. The research moves past a “one-size-fits-all” approach to explore how 29 separate biological, psychological, and social factors tightly interlock.
By aggregating expert consensus to isolate 175 distinct causal connections, the study illustrates how everyday variables, such as screen habits, stress, smoking, and bodily inflammation, feed into thousands of self-reinforcing, circular loops that trap individuals aged 18 to 40 in chronic psychiatric distress.
Key Facts
- Shattering Single-Cause Theories: Public health discussions frequently blame a single scapegoat, such as smartphone habits or academic school structures, for the rising youth mental health crisis. Co-author Professor Naja Hulvej Rod notes that this study shifts the paradigm by demonstrating that many interwoven factors dictate psychiatric well-being.
- The Interlocking Nicotine Loop: To illustrate the complexity, Assistant Professor Jeroen Uleman highlighted how nicotine use creates a vicious feedback loop. Smoking can trigger depressive symptoms that fracture sleep. To battle the resulting daytime fatigue, individuals often smoke more, introducing excess nicotine that further degrades sleep quality and actively deepens their depression.
- A 14-Expert Multidisciplinary Brain Trust: The structural model was constructed by bringing together 14 top-tier experts across sleep research, psychology, sociology, epidemiology, and biology to pinpoint causal relationships and cross-verify existing scientific literature.
- A Living, Scalable Diagnostic Tool: The researchers emphasize that their model is a living framework rather than a fixed, static explanation. The system is designed to scale dynamically, allowing future scientists to plug in emerging political, economic, or environmental variables.
- Immediate Local Policy Application: Fueled by an upcoming public health act mandating local wellness strategies, the framework is already being utilized on the ground. Through a partnership with the Faaborg-Midtfyn Municipality, local policymakers and practitioners are using the model to guide real-world well-being interventions for children and youth.
Source: University of Copenhagen
Among the younger part of the population, sleep problems, anxiety, and depression are widespread and growing issues.
But why are our sleep and mental health in such poor condition? And why does it seem so difficult to improve the situation?
New research from the University of Copenhagen aims to shed more light on these questions.
In a new study, researchers map how a range of biological, psychological, and social factors – such as stress, screen habits, and smoking – interact, and how they may create self-reinforcing cycles that risk keeping young adults in poor mental health.
“We know that poor sleep and depressive symptoms often go hand in hand, but with our mapping we now better understand how a range of other mechanisms may potentially keep the problem alive.
“This gives us a more nuanced picture of why it can be so hard for young people to break out of these self-reinforcing ‘vicious cycles’,” says Assistant Professor Jeroen Uleman from the Copenhagen Health Complexity Center, one of the researchers behind the new study.
A complex public health crisis
In the study, the researchers map how 29 factors influence one another in young adults aged 18 to 40.
The model illustrates how sleep disturbances can worsen depressive symptoms, which in turn affect sleep, and how factors such as stress, screen habits, physical activity, social relationships, nicotine use, and bodily inflammation may play into a wide range of self-reinforcing loops.
An online, interactive version of the model is available here.
“Our model illustrates, for example, how smoking may potentially lead to depressive symptoms, and how these symptoms can disrupt your sleep. You may then smoke more to counter increasing fatigue, while nicotine affects your sleep quality, which again may worsen depressive symptoms. Other loops are even more complex,” says Jeroen Uleman.
This complexity is precisely what needs to be uncovered, notes Professor of epidemiology and co-author of the study, Naja Hulvej Rod:
“Instead of focusing only on single causes behind the growing sleep and mental health crises among young adults – such as smartphone use or how we structure our school system – our study shows that many factors are involved.
“And that these factors are tightly interwoven in a complex network that we need to understand in order to figure out how to break these self-reinforcing cycles,” she says.
Experts identified key connections
The researchers built the model by inviting 14 experts in fields including sleep research, psychology, sociology, epidemiology, and biology to propose important factors, assess causal relationships between them, and highlight scientific literature supporting the connections.
So far, the experts and researchers behind the study have identified 175 causal connections between the individual factors and many thousands potential self-reinforcing loops.
The researchers emphasize, however, that they have not conducted empirical investigations of the many ‘vicious cycles’, and further research will therefore be needed to understand their effects.
The model should also not be seen as an exhaustive explanation of young people’s sleep and mental health. Instead, the researchers see it as a living tool that can be continuously updated with more factors from additional disciplines – such as political or environmental dimensions – and further supported and expanded through additional research.
Supports local interventions
The model can help highlight possible intervention areas – for example in municipalities, which, because of the upcoming public health act, will be responsible for strengthening public health locally, including mental health.
Today, the Copenhagen Health Complexity Center at the University of Copenhagen, led by Naja Hulvej Rod, has a partnership with Faaborg-Midtfyn Municipality to improve the well-being of children and young people, including within sleep – and here, the model has been useful.
“There have already been workshops with practitioners in the municipality, where we provided input from our model. This way, decisions can be made based on both lived experience and scientific evidence. Our hope is that the model can be used in political decision-making processes in municipalities across the country as the public health act is implemented,” says Naja Hulvej Rod.
Faaborg-Midtfyn Municipality is also excited about the collaboration.
“Our collaboration with the Copenhagen Health Complexity Center at the University of Copenhagen provides us with professional evidence that we can compare with our experiences in the municipality.
“In this way, our partnership with the researchers inspires us to identify where it makes sense to intervene in relation to the well-being of our children and young people – both now and in the long term.
“Furthermore, it is immensely meaningful that the general insights generated through the collaboration can benefit everyone,” says the mayor of Faaborg-Midtfyn Municipality, Anstina Krogh.
Key Questions Answered:
A: Because depression and poor sleep aren’t isolated, independent glitches; they are part of a massive, hyper-locked system. The University of Copenhagen proved that when a young adult falls into poor mental health, a giant web of 29 different lifestyle factors locks arms around them. Breaking out requires fighting against thousands of invisible, self-reinforcing loops where a bad day at work feeds into screen binging, which breaks sleep, which drives nicotine use, which deepens depression. It is a complex spiderweb, not a lack of willpower.
A: Human beings naturally long for simple answers to impossibly massive problems. It is incredibly easy to point at smartphones or school schedules and say, “That is the single reason our youth are struggling.” While screen habits are a key piece of the puzzle, this research proves that focusing exclusively on one variable is an ineffective strategy. Everything from biological inflammation to social connections is tightly interwoven, meaning we have to treat the whole interconnected lifestyle web to make a lasting impact.
A: It takes the guesswork out of local funding and policy decisions. Instead of guessing which health programs to create, municipalities like Faaborg-Midtfyn are matching their real-world, local experiences directly against the scientific evidence in this model. By running specialized workshops with local practitioners, they can see exactly where an intervention will disrupt a vicious loop, allowing them to build hyper-targeted, long-term well-being programs that actually keep kids safe.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this mental health research news
Author: William Brøns Petersen
Source: University of Copenhagen
Contact: William Brøns Petersen – University of Copenhagen
Image: The image is credited to Neuroscience News
Original Research: Open access.
“The Young Adult Sleep model: an evolving causal loop diagram of mental health dynamics” by Jeroen F. Uleman, Rushd F. M. Al-Shama, Adrian G. Zucco, Jette Echterhoff, Maartje Luijten, Maaike Verhagen, Jana Vyrastekova, Jorien L. Treur, Robyn E. Wootton, Sicelo Jones, Martin Dresler, Henning J. Drews, Christine Egebjerg, Birgitte R. Kornum, Karien Stronks & Naja Hulvej Rod. BMC Medicine
DOI:10.1186/s12916-026-04738-7
Abstract
The Young Adult Sleep model: an evolving causal loop diagram of mental health dynamics
Background
This study introduces the Young Adult Sleep model, a comprehensive causal loop diagram (CLD) developed to explore the dynamic feedback mechanisms underlying sleep problems and affective depressive symptoms in young adults—an urgent public health challenge.
Methods
The CLDs was developed through five asynchronous questionnaire-based assignments completed by a panel of 14 domain experts, two existing CLDs, and targeted reviews of the scientific literature. Natural language processing was used to curate the system variables from questionnaire data.
Results
The CLD integrates extensively interconnected variables across biological, psychological, behavioral, and social domains. It comprises 29 variables and 175 causal connections, forming numerous reinforcing feedback loops that can drive “vicious” cycles, such as the interplay of sleep disturbances and affective depressive symptoms with addictive behaviors like smoking.
The experts also identified balancing loops that may counteract these self-reinforcing dynamics. Many loops span multiple domains, underscoring the importance of multidomain interventions and of interdisciplinary research that synthesizes evidence across scientific fields.
Conclusions
The Young Adult Sleep model is an evolving CLD framework that is intended to be further refined as new evidence becomes available. It supports iterative theory development and hypothesis generation, and serves as a foundation for future computational modeling to simulate intervention strategies to address this complex public health problem.
