Of the 1504 participating adolescents, 1477 (98%; 56% females) completed all three MISS items and were thus included in the analysis. Over 90% of the participants perceived their family financial situation as being good or average, and two-thirds (67%) of respondents declared their self-reported health to be good or very good. Insomnia was reported in 22% of the study group, (18% of females and 27% of males), and the median age was 16 years (range 15–17 years).
The bivariate analysis (Table 1
) showed that insomnia was associated with being male, a poorer perceived family financial situation, having poor self-reported health, infrequent physical activity (≤1 time/week), having failed at least one school course, and a monthly use of alcohol and/or cigarettes (p
< 0.05). However, school start time before or after 08:30, and time spent on social media and/or gaming ≥4 h/day were not associated with insomnia (Table 1
The logistic regression analysis showed that insomnia was associated with being male (OR: 1.4), poor self-reported health (OR: 4.2), failed school courses (OR: 1.4), and monthly use of alcohol and/or cigarettes (OR: 1.4). There was no significant association between insomnia and school start time, perceived family financial situation, physical activity, or spending ≥4 h/day on social media and/or gaming (Table 2
We then investigated possible combined effects between self-reported health and physical activity on insomnia (Table 3
). In this analysis, insomnia was associated with failed school courses (OR: 1.6), monthly use of alcohol and/or cigarettes (OR: 2.1), infrequent physical activity (≤1 time/week) and good self-reported health (OR: 1.7), physical activity (≥2 times/week) and poor self-reported health (OR: 11.9), and infrequent physical activity (≤1 time/week) and poor self-reported health (OR: 18.9).
The aim of the study was to investigate the association between insomnia, academic performance, self-reported health, physical activity, school start time, and substance use among adolescents. Our results show that insomnia was present in 22% of the participants, and that it was more common in males than in females. Further, poor self-reported health, failed school courses, and monthly alcohol or tobacco use were also associated with insomnia in Swedish adolescents. When the combination between self-reported health and physical activity was tested, physical inactivity was also found to be associated with insomnia, and the effect of the combination was strikingly greater than either factor alone.
In the present study, poor self-reported health was correlated with insomnia. Similarly, Roberts et al. [9
] demonstrated that insomnia is correlated with future health. Insomnia increases the risk for health problems such as anxiety and depression [9
]. Insomnia may also come from mental problems such as depression and anxiety disorders, and, therefore, interventions targeting both sleep hygiene and psychological aspects are recommended [28
]. Adolescents with insomnia are more likely to seek medical care in the future [9
In this study, insomnia was more common among males than among females. However, females were also more physically active than males in this study; thus, it is likely that physical activity—rather than gender—affected insomnia. In other words, inactive adolescents with poor self-reported health are eighteen times more likely to have insomnia relative to active adolescents with good self-reported health. The World Health Organization estimates that 1.9 million deaths worldwide that are related to chronic disease can be attributed to physical inactivity so it is important to promote active lifestyles [29
]. Physical activity may be used as an effective non-pharmacological intervention for improving sleep quality [11
]. A meta-analytic review showed that physical activity had positive effects on sleep duration and sleep quality over time [30
]. However, a systematic review [31
] contended that exercise must be further evaluated to judge its usefulness in the treatment of insomnia. It is unknown what kind of exercise or what “dose” may be most efficient.
Furthermore, our results revealed that failed school courses were associated with insomnia. Similarly, Zhao et al. [32
] reported associations between poor school performance and insomnia among adolescents aged 11–20 years. Worries about failing courses might lead to insomnia. However, given that sufficient sleep is crucial for cognitive functioning and memory consolidation, insomnia might also lead to poor academic performance or both issues may be due to other health problems, such as depression, that may impact both sleep and cognitive performance [33
Another finding was that the monthly use of alcohol and/or cigarettes was associated with insomnia. Similarly, a study of Japanese adolescents showed that insomnia is prevalent and associated with multiple factors, such as poor mental health, monthly alcohol consumption, and smoking [34
]; and another study among adolescents (aged 10–21 years) in North America also reported correlations between substance use and sleep disturbances [35
]. Poor sleep has been found to be a predictor of substance use among adolescents [16
]. Understanding the association between reducing adolescents’ substance use and its effects on insomnia is important for informing the best ways to promote sleep health in this population. A bidirectional relationship between substance use and insomnia has been proposed in which sleepy adolescents may use nicotine to become more alert during the days and consume alcohol in the evenings to facilitate sleep. Both nicotine and alcohol have, however, sleep disturbing effects and thus vicious cycles are maintained [36
School start time was not associated with insomnia in the present study. Delayed school start time by one hour has been found to be associated with improved alertness, mood, and health among adolescents in a study by Lufti et al. [37
]. A Cochrane review regarding high school students showed that a number of school systems worldwide have proposed and implemented later school start time, and there are potential associations between later school start time, academic performance, quality of sleep, and mental health [38
]. No studies have been conducted in Sweden, and further studies with a long-term follow up is therefore called for.
The results of the present study can serve as a stepping stone for future research on how society can increase the health and well-being of adolescents experiencing insomnia. Engagement and motivation are crucial aspects that must be addressed in order to change sleep-related behaviors in adolescents. One approach for doing so is the use of motivational interviews, which was found to be effective at extending adolescents’ sleep duration [39
]. Parent-set bedtimes have also been found to be beneficial for teenage sleep [40
]. Adolescents, guardians, schools, and society in general must adopt a health-promotion framework that includes listening to the adolescents’ thoughts and concerns. Nonetheless, adolescents are well-aware of the importance of adequate sleep [41
], yet more work remains to be done to motivate adolescents to establish healthy sleep habits.
Strengths and Limitations
The strengths of the current study include the large sample size. However, one limitation of self-reported data is that answers can vary from day to day according to external and internal circumstances. Given that the questionnaire was completed during the school day, it may be that adolescents viewed that a completion of the study as mandatory, regardless of the fact that they were clearly informed that a participation in the study was voluntary. Cross-sectional designs cannot determine causal relationships [43
]. Other limitations are that questions regarding anxiety or daytime tiredness were not included, and that some of the included questions were single items. The items were dichotomized, which can increase the risk of overlooking nuances in the result; however, this was done as a result of low response frequencies on some response alternatives, and also to facilitate data interpretation.