Background: As the number of Internet users around the world increases, so does the dependency on the Internet. In adolescents this dependence interferes with sleep, which is important for the development of their psychophysiological capabilities. However, few large-scale surveys have examined the relationship between internet addiction (IA) and sleep disturbance in detail using standardized questionnaires. This study aimed to determine the relationship between sleep disturbance in adolescents and IA according to the categories of the Young Diagnostic Questionnaire (YDQ) through a complete survey of one prefecture in Japan.
Methods: In 2016, a self-administered questionnaire was used to survey high school students (n=10,405) in all 54 daytime high schools in one prefecture. In this study, “sleep disturbance” was defined as achieving over 5.5 points on the Japanese version of the Pittsburgh Sleep Quality Index. IA was evaluated using the YDQ: “IA,” when 5 of the 8 YDQ items were applied; “at-risk,” when either 3 or 4 YDQ items were applied; and “non-IA,” when less than 2 YDQ items were applied. Multiple logistic regression analysis was performed, with sleep disturbance as the dependent variable, IA as the explanatory variable, and adjustments made for 8 items, including the frequency of skipped meals.
Results: High YDQ scores were associated with high prevalence rates of sleep disturbance in both male and female participants; the higher the score, higher was the rate. On multiple logistic regression analysis for both male and female participants, higher YDQ scores showed higher adjusted odds ratios for sleep disturbances.
Conclusions: For high school students within one prefecture in Japan, higher YDQ scores, which indicate internet dependency, were significantly related to sleep disturbance, suggesting that the likelihood of sleep disturbance increases with YDQ scores.
Study population and design
Upon obtaining the consent of the President of the Association of High School Principals and the prefectural Education Bureau of a certain prefecture in Japan, we sent requests for participation to the principals of all 54 daytime high schools within the above prefecture and mailed the following documents to each principal: (1) letter requesting cooperation, (2) planning document containing the study purpose and method, and (3) the survey form to be used in the study. We stated that a self-administered questionnaire form would be used in the survey and ensured that the privacy of the survey respondents would be protected. There were a total of 10,405 students in the 54 daytime high schools.
The survey procedure was as follows: (1) the teachers distributed the following three items: an “explanatory document,” a “self-administered questionnaire form,” and an “envelope;” (2) after filling in their responses in the questionnaire form, the surveyed students placed the completed questionnaire form in the provided collection envelope and sealed the envelope; (3) the teachers collected the sealed envelopes; (4) the envelopes containing the self-administered questionnaire forms were first unsealed and opened when they were to be used for data input at the assigned research facility. The survey period was from June to December 2016.
The survey forms collected information on the following five items:
Cooperation of students in the present study was voluntary. As our cohort included adolescents aged 15–16 years, we obtained written informed consent either directly from the students if their supervising teacher confirmed that their judgement was acceptable or from their parents if the supervising teacher thought that the parents' judgment was necessary. The following items were stated on the explanatory document distributed to students or their families: (1) the survey was part of an epidemiological study and that involved neither an evaluation for school grading nor any type of punishment, (2) the students were free to cooperate in the survey and failure to cooperate would not incur any disadvantage, (3) the school teachers would not view the responses provided, and (4) privacy would be strictly protected. In the present study, the ethics committee of the organization with which the authors are affiliated approved the study (Reference No. 932).
Students who did not completely fill out the J-PSQI and the YDQ were excluded from the analysis. First, distribution by sex (male or female) was plotted for J-PSQI and YDQ scores. Next, prevalence rates for different categories of sleep disturbance and IA were calculated separately for each sex using the chi-squared test. Furthermore, for each of the three YDQ categories, sleep disturbance prevalence rates were calculated for each sex separately. Finally, multiple logistic regression analysis was performed to investigate the relationship between IA (explanatory variable) and sleep disturbance (dependent variable). The type of school, school-commute time, sports and club time, outside-class study time, television viewing time, skipped meals, depressed mood (mental health), and school-life satisfaction rates were used as the adjustment factors. Statistical Package for Social Sciences version 22 (SPSS, IBM Corp. NY, USA) for Windows was used for statistical analyses. A p-value < 0.05 was considered significant.
Of the 54 schools (n=10,405) that were requested to participate, 40 schools responded positively. At the time of the study, there were 7,186 first-year (of 3 years) high school students, among whom 6,950 provided responses. The response rate was 96.7%. Of these, 5,264 students (2,635 males, 2,629 females) provided informed consent (effective response rate: 73.3%). Figure shows the distribution of J-PSQI and YDQ scores. In both males and females, symmetrical distribution with a cutoff value of 5.5 points was observed for J-PSQI scores. With regard to the YDQ scores, 0 point was the most frequent score for both males and females, with higher scores presenting less individuals.
Table 1 shows the percentages of students having sleep disturbance and the number of subjects included within the three YDQ categories. Students defined as having sleep disturbance comprised 50.5% of all subjects. In both male and female participants, a higher percentage of sleep disturbance was observed in the following groups: private high school, students with high frequency of skipped meals within a 1-week period, and students with high frequency of depressed mood (mental health). Overall, based on the YDQ scores, 9.4% of males and 14.8% females were classified as IA, while 23.1% of males and 28.1% of females were at high risk. In both males and females with IA, we observed a high percentage of students with high frequency of skipped meals, depressed mood (mental health), and low school-life satisfaction. Furthermore, males with IA spent less time engaging in school sports or in clubs, while females with IA spent less time on outside-school study. With regard to at-risk males and females, the frequency of depressed mood (mental health) and low school-life satisfaction was high. At-risk females also did not spend much time on outside-school study.
Table 2 shows the rate of students with sleep disturbance for each of the three categories of YDQ. In both males and females, the higher the YDQ score in any category, the higher the rate of students with sleep disturbance.
Table 3 shows the results of the multiple logistic regression analysis on the relationship between YDQ categories and sleep disturbance. We observed in both males and females, the higher the YDQ score in any category, the higher the value of the adjusted odds ratios in sleep disturbance.
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 . 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 .
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 . Chen et al. also reported that IA predicted “disturbed circadian rhythm” leading to sleep disturbance , 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 .
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 . In another study individuals with IA reportedly had reduced gray matter density . 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  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.
In the future, more longitudinal surveys that investigate the factors related to the occurrence of IA and sleep disturbance should be conducted. In addition, if interventional studies are conducted, their findings can be integrated in the evidence-based health education.
IA: Internet addiction
YDQ: Young Diagnostic Questionnaire
J-PSQI: The Japanese version of the Pittsburgh Sleep Quality Index
J-YDQ: The Japanese version of the Young Diagnostic Questionnaire
Ethics approval and consent to participate
The participation of students in the present study was voluntary. Our cohort included adolescents aged 15–16 years, but all eligible students had completed junior high school courses. The following items were stated on the explanatory document distributed to students or their families: (1) the survey was part of an epidemiological study and that it involved neither an evaluation for school grading, nor any type of punishment; (2) the students were free to choose whether to participate in the survey and that failure to participate would not incur any disadvantage; (3) the school teachers would not view the responses provided; and (4) their privacy would be strictly protected. This survey was conducted on students who had parental consent and who agreed in writing. In the present study, the ethics committee of the organization with which the authors are affiliated approved the study (Reference No. 932).
Consent for publication
Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available due to the sensitive nature of the raw data but are available from the corresponding author on reasonable request.
The authors declare that they have no actual or potential competing financial interests.
This study was supported by the Grant-in-Aid for Scientific Research (JP 17K09117).
The funding bodies have no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.
MT, YK, OI, and YO conceived the Questionnaire and MT, YK, OI, and YO conducted the survey. MT wrote the initial draft and had the responsibility for submitting for publication. YK, OI, and YO performed a critical revision of the manuscript. MT conducted the initial analyses. YK, OI, and YO provided important feedback on how the study can be improved. All authors have read and approved the final manuscript.
We express our deep gratitude to all of the high school students and their teachers who cooperated in this study. We also express our heartfelt thanks to Yukiko Abe for her cooperation in collecting survey forms and in the analysis work. We would like to thank Editage (www.editage.com) for English language editing.