Background
Going to university is associated with changes in lifestyle, with increasing autonomy in personal life. Students’ social environment changes, as many move out from their parents’ homes into shared or single flats [
1]. Highly variable starting times for university lectures and seminars in the morning often lead to changing sleeping patterns [
2]. University students are at high risk for developing sleep problems, with symptoms such as difficulties falling asleep, frequent night awakenings, nightmares [
3] and daytime impairments [
2]. Risk factors, e.g. rising late, short sleep durations and non-restorative sleep concern especially university students. Many report bedtimes differing more than 2 h on weekdays and weekends [
4]. Nevertheless, previous findings are inconsistent in terms of reported percentages of serious sleep disorders in university students and in the general population [
5]. The highest prevalence of poor sleep quality and occasional sleep disturbances (73%) was reported for US university students [
6]. Current estimates of the percentage of university students all over the world fulfilling diagnostic criteria for insomnia range from 9.4–13.1% [
2,
7,
8]. Sleep disorders, poor sleep quality and excessive daytime sleepiness is associated with lower academic motivation and lower self-efficacy [
9]. In university students without depression, poor sleep quality has been linked to lower academic performance [
9]. Sleep disturbances often occur during high-stress periods, with stress and sleep disturbances increasing over a 4-year period in Canadian university students [
10]. Concerning the widespread influences of disturbed sleep on learning and other cognitive functions in students, an experimental study showed that students are not aware of the impact of sleep restriction on their academic performance [
11]. They overrated their academic performance after total sleep deprivation. This could result in poorer academic performance in many European universities without the students knowing why. In addition, Daley and colleagues showed that insomnia was associated with less work productivity, increased health care utilization and work absenteeism [
12]. Moreover, insufficient sleep is also a risk factor for burnout [
13].
In addition to sleep and insomnia, other factors have been shown to affect university students’ well-being. For example, chronotype is associated with stress responses [
14]: evening-types are more vulnerable to stress, and show impaired academic motivation. This association, is mediated by daytime sleepiness. An association between chronotype and academic performance has also been demonstrated in a Turkish sample of university students [
15]. Evening-types are assumed to be at an academic disadvantage with exams and lectures mostly scheduled in the mornings. In contrast, higher self-efficacy is associated with better academic performance, self-regulation, mental health and fewer sleep disturbances [
16].
Thees et al. [
17] investigated self-reported health in German university students. The majority of participants reported elevated stress levels after the change from the previous higher education system to the Bologna system. In their study, prevalence rates for different impairments were assessed for a range of physical complaints such as headaches, stomach aches, sleeping problems, back pain and muscular tension. 44.6% reported regular muscular tension, 30.6% back pain, 9.3% tinnitus and 20% sleep disturbances. In total, about one quarter reported ill health. In a sample of 1130 university students at a German university, 22.7% fulfilled criteria for a mental disorder excluding alcohol syndrome [
18]. Most prevalent among university students were depression (14.1%) and somatoform syndrome (9.1%). Nevertheless, sleep quality was not included in Bailer and colleague’s study. In another large study concerning health of college students and non-college attending young adults, 45.8% of college students had a mental disorder [
19]. Again, sleep disorders were not considered in the analysis. Alcohol syndrome was the most common disorder, 20.3% of all college students reported an alcohol-related disorder [
19]. These were the only syndromes more frequent in college students than in their non-college-attending peers. Mood disorders, anxiety disorders, and personality disorders were less prevalent in college students than in their non-college peers. Various studies have demonstrated, that mental health and insomnia are often related to lower academic grades [
8,
20], and it is estimated that 3.2–11.4% of college non-completion variance is explained by mental disorders [
8].
Gender differences in psychological distress have also been found in European university students. Women are significantly more often affected (OR = 1.8) by a mental disorder than men, excluding alcohol syndrome [
18]. In a large Turkish sample, female university students indicated significantly higher stress and anxiety scores compared to male students [
21,
22]. Furthermore, higher test anxiety is significantly related to lower performance in tests, and female university students are significantly more often impaired than male students [
23].
Various components of mental strain interact. Sleep problems co-occur regularly with various mental health impairments, as depression, anxiety disorders, and substance abuse in college students [
8]. Depression, anxiety, and sleep problems often co-vary and influence each other [
24,
25]. Chronotypes correspond differently to stress, which influences sleep quality and quality of life as a result [
14,
26]. A high impact of self-efficacy on depressive and anxiety symptoms, as well as sleep quality, was reported [
14,
27]. Even after controlling for trait anxiety, self-efficacy influenced internalizing symptoms significantly [
27].
The aim of this study, therefore, was to evaluate sleep disturbances, mental strain and self-efficacy in two samples of university students from two different German speaking EU countries, and relate these to mental strain. We wanted to examine [
1] if German and Luxembourgish students report an equal level of sleep disturbances, as well as equal sleep duration, sleep-onset latency, daytime sleepiness, and amount of chronotypes due to cultural similarities and largely similar educational systems. Hence, [
2] if depression and other mental strains are on the same level in both countries. Thirdly, [
3] if gender differences concerning sleep quality, chronotype, depression, measures of anxiety, and self-efficacy are equal as shown in previous studies.
Discussion
Our analysis of students from Germany and Luxembourg revealed that for all variables concerning sleep quality and mental strain both countries were equally affected, which is in line with our hypotheses.
Subjective sleep quality did not differ between German and Luxembourgish students. However, in mean the students scored above the cut-off for clinical significance concerning sleep disturbances—as measured by the PSQI [
39]. Although, subscales of the Pittsburgh Sleep Quality Index did not differ between countries, a total of 42.8% of students indicated symptoms of impaired subjective sleep quality above the cut-off, and 17.9% reported symptoms of a clinically relevant sleep disorders. These prevalence rates are below previously reported findings on impaired sleep quality [
6] but higher than estimates insomnia diagnosis in this population [
2,
7,
8]. Nevertheless, mean daytime sleepiness (measured by ESS) was not above the cut-off. Other researchers found the highest cognitive impairments due to sleep problems and 50% experience excessive drowsiness, among university students compared to employed young adults and adolescents [
40]. In the US, findings suggested that among other health related factors such as exercise, nutrition, mental health and stress management, healthy sleep habits have the highest predictive value for success in college [
41]. Eden [
9] concluded that excessive daytime sleepiness and low self-efficacy lead to lower academic motivation and lower academic performance.
In addition to impaired sleep quality, 18.8% reported sleep-onset latency of more than 30 min, which can be interpreted as a symptom indicating
insomnia. In the study conducted by Taylor and colleagues [
8], the relationship between insomnia and mental health problems was no longer significant after controlling for comorbid health problems even though they often co-occur. Sleep duration less than 7 h is not recommended for this age group, however, 32.6% of all students sleep less and are at risk for health problems [
42].
Concerning
mental strain, approximately 27.1% of all students suffered at least from moderate symptoms of depression. We found a slightly elevated level of depressive symptoms, and stress and signs of social anxiety for the whole sample. About 19.8% of students reported clinical relevant symptoms of social phobia, although the majority of students did not reach the cut-off for social phobia as measured by the SIAS. These prevalence rates are higher than reported by another sample of German university students, in which 14.1% fulfilled the criteria for a depressive disorder and 4.6% criteria for any anxiety disorder [
18]. Even though there were no significant differences between countries in
depression, stress, social phobia and
fear of exams, a critical number of students seemed to be impaired in both countries. Academic success seems to be impaired by symptoms of depression as detected in the US and in a large sample of adolescents in Finland [
43] and perceived stress and self-efficacy influenced academic performance [
44], also these results are important for a university career. Beyond, in college freshmen, self-efficacy was a robust and consistent predictor of academic success, even more than stress. We found nearly one-quarter of our students reported clinically relevant impairments. These results demonstrate that university students have impairments in depression as well as a high stress level. Underlying mechanisms should be uncovered and implications for interventions should be developed.
As
self-efficacy seems to be a central factor of sleep and mental health in university students it would be good to improve resources, as increase self-efficacy in university students. Various studies demonstrated that higher self-efficacy is known to be associated with less sleep problems [
2] and less nightmares [
3]. Self-efficacy is significantly lower in female university students than in male as reported in previous studies [
45,
46].
Concerning
gender, in the present sample female students in both countries reported significantly lower sleep quality compared to male students, which is in line with previous studies, showing lower sleep quality in female university students [
2]. These findings suggest women in both countries being more vulnerable for disturbed sleep. Women tended to report more sleep disturbances and more daytime sleepiness. Chronotype was significantly different between genders, with more men reporting a slightly later chronotype, even though a later chronotype has been found to be a risk factor for disturbed sleep [
47]. In addition, women tended to be more depressed, more stressed and reported more test-anxiety. These results are in line with previous findings [
18,
23]. In a large global sample, Seedat and colleagues [
48] found women had a higher risk for anxiety and mood disorders. Except for social phobia, these findings are in line with our sample. Interestingly, men and women report an equal number of symptoms of social phobia but this phenomenon has also been previously shown [
49]. Considering these results, more attention should be paid to female students’ mental health.
The number of
semesters studied showed a significant effect on sleep quality, social phobia, and test anxiety. Students in higher semesters reported fewer sleep problems and less anxiety. This is in contrast to previous findings which reported more mental health problems in higher semesters as health problems often co-occur with studying longer than 13 semesters [
50]. However, our results are more in line with other authors, who found the highest level of sleep disturbances and stress in the first year [
51].
All reported variables have an impact on subjective quality of life, which highlights the importance of further research to encounter mechanisms underlying the difference in sleep patterns in different countries. The increase in negative affect when sleep deprived [
52] might lead to a vicious circle of sleep deprivation, negative affect, lower academic success, more negative interactions and lower quality of life. Further impairments including heavy drinking and physical inactivity have been concluded to be the consequence of sleep problems [
53]. In addition, variables like physical activity, consummation of drugs and other health-related factors should be included in further studies. The findings in the present sample underline the importance of interventions especially designed for students.
Some
limitations should be named. The high number of women (73.3% in the current sample; 48.0% in German universities; [
54]) and very unequal sample sizes in Germany and Luxembourg might impair the generalizability of these results. Women always showed an elevated health risk and a higher stress level, so all results could have overrated the real impairments in European students [
6]. Nevertheless, the current sample size is large, and all measurements were self-reports. Other than that the encountered difference in sleep disturbances between countries could be due to different cities or other factors having an impact on sleep, like stress in the specific study-subject, alcohol and drugs (Luxembourg is much closer to Holland and its legalized Marihuana) or different living environments (shared flats, student residence, living with parents). Culturally the two countries seem not very different. Furthermore, only two countries took part in this study and generalizability to other countries might be limited. The number of semesters was included in the analysis even though we had no information on degree, so the validity of this analysis is limited. More detailed analyses of different schedules in various disciplines might show impact on university students’ lives even though previous studies showed no influence on sleep quality or mental health [
18,
55]. Variables worthy of consideration in further studies might be part-time or full-time studies, the number of children or jobs besides studying. Furthermore, in the present study, other comorbid health problems were not assessed even though previous research shows a strong relationship between pain and sleep [
56]. Comorbid health problems might interact with mental health problems and insomnia symptoms [
8].