Why are young people's sleep and mental health so poor? Researchers point to 'vicious cycles'
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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?
A new study from the University of Copenhagen maps 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. The research is already being used to target interventions for young people in a Danish municipality.
"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 published in BMC Medicine.
A complex public health crisis
The researchers mapped how 29 factors influence one another in young adults aged 18 to 40. Their 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 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 of 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 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 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.
About the study and the method
The study identifies numerous self-reinforcing cycles that potentially keep young people trapped in mental distress and poor sleep patterns.
The loops consist of 29 factors and 175 causal connections across biological, psychological, behavioral, and social dimensions—such as links between smoking, sleep disturbances, physical health, loneliness, and socioeconomic status.
The model is based on expert knowledge and existing literature, but systematic reviews of all 175 causal connections or empirical studies of each loop have not been conducted. Further research is needed to understand the public health effects of the loops.
Expert-driven methods also carry a risk of subjectivity and potential overrepresentation of certain fields. Finally, the model does not cover all possible influences on sleep and depressive symptoms—such as environmental or political factors.
The model is therefore not an exhaustive explanation of young adults' problems with sleep and mental health but should be seen as a "living tool" that should be continuously updated and used to inform policy processes.
Publication details
Jeroen F. Uleman et al, The Young Adult Sleep model: an evolving causal loop diagram of mental health dynamics, BMC Medicine (2026). DOI: 10.1186/s12916-026-04738-7
Journal information: BMC Medicine
Key medical concepts
DepressionSleep DisordersAnxiety DisordersTobacco Use DisorderInflammation
Clinical categories
Sleep medicinePsychiatryPsychology & Mental healthSleep & Recovery Provided by Niels Bohr Institute Who's behind this story?
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