The present study aimed to determine the relationship between sleep disturbance in adolescents and IA. We found a relationship between adolescent sleep disturbance and IA in one prefecture in Japan and found that sleep disturbances are more prevalent in categories with higher YDQ scores. Besides, the results of the multivariate analysis revealed significantly higher adjusted odds ratios between categories with high YDQ and sleep disorders, suggesting a significant relationship between higher YDQ scores (3-4 or ≥5) and sleep disorders.
Using the PSQI and YDQ to investigate the relationship between sleep disturbance and IA in high school students, we found that the categories with higher YDQ scores showed high values for the adjusted odds ratio of students with sleep disturbance (Table 3). This relationship is similar to that reported by Bakken et al. among Norwegian adults aged 16 years or older, where individuals with high YDQ scores had significantly higher sleep disturbance prevalence rates than did non-problematic internet users [40]. Furthermore, the present study found differences between sexes, with a higher sleep disturbance adjusted odds ratio in girls with IA than in boys. This finding is similar to the results of Durkee et al., who confirmed a significant relationship between insufficient sleep and IA in female participants, which is in line with the findings in a previous study [22].
There are several possible mechanisms for the relationship between sleep disturbance and IA. Our findings suggest that IA itself results in sleep disturbance, which is in line with a previous study reporting problematic internet use to be a significant predictor of sleep disturbance [20]. Chen et al. also reported that IA predicted “disturbed circadian rhythm” leading to sleep disturbance [23], which despite the lack of long-term prior research can explain why IA leads to sleep disturbance.
The second mechanism is the reverse of the one discussed above, where sleep disturbance might lead to the development of IA. In a longitudinal study, Chen et al. reported that difficulty in falling asleep and nocturnal awakening were predictors of IA [23].
A third possible mechanism is the simultaneous occurrence of both abovementioned mechanisms, where sleep disturbance occurs after the development IA and IA develops due to sleep disturbance. Several studies have confirmed that in brain imaging, both sleep disturbance and IA cause changes in the gray matter [41, 42]. A study of retired military personnel showed that regardless of any coincidental psychiatric state, individuals with a high PSQI score presented with reduced volume of the entire cortex and the frontal lobes [42]. In another study individuals with IA reportedly had reduced gray matter density [41]. These findings suggest the possibility that sleep disturbance and IA cause the same organic (structural) changes in the gray matter, indicating a hypothesis that sleep disturbance and IA may occur simultaneously.
However, the fourth mechanism is also possible, where although sleep disturbance and IA are not truly related, a third factor common to both links them together, with the end-result being an observed relationship between sleep disturbance and IA. In our present study, we adjusted the lifestyle factors related to adolescence and excluded the effects of confounding factors in our multivariate analysis. Nevertheless, there is a possibility that the separate confounding factors, which were not adjusted for, exist.
The following four points can be considered as the strengths of this study. First, the sample size was sufficient. Second, to investigate the relationship between sleep disturbance and IA, we used the PSQI and YDQ, which have been frequently used as standard indices in several epidemiological surveys [5, 10, 22, 28, 30, 32, 40, 41, 43-48]. Third, in our analysis, we evaluated the relationships between sleep disturbance and IA for each of the three categories of the YDQ, including at-risk internet use; this category has not been sufficiently investigated in prior epidemiological studies. Fourth, we considered several lifestyle factors that may be involved in IA in adolescence.
Nonetheless, the present study also has a number of limitations. First, the present study deals with the results of a cross-sectional survey, which means that we cannot formulate any conclusion about the direction of causality. Second, we did not adjust all the items, which may be related to IA. For example, we did not ask questions about other psychiatric disorders like attention deficit and hyperactivity disturbance (ADHD), which is reportedly associated with IA [49-51] and sleep disturbance [51] in adolescents. In the present study, all subjects were enrolled as daytime high school students, with all subjects regularly attending school. In such a case, the number of students with ADHD is considered low. Third, as we performed the survey within each of the schools, non-attending students could not participate. In the future, efforts to conduct a survey that will enable participation of non-attending students should be made. Fourth, our survey population was limited to students in a single prefecture in Japan; hence, there was certainly a sampling bias.