Abstract

Objective To study association between nocturnal mobile phone use and mental health, suicidal feelings, and self-injury in adolescents. Methods Associations of mobile phone use after lights out with mental health, suicidal feelings, and self-injury were cross-sectionally examined in 17,920 adolescents using a self-report questionnaire. A series of logistic regression analyses were separately conducted for early (grades 7–9) and late (grades 10–12) adolescents. Results Sleep length was significantly associated with the mobile phone use only in early adolescents. Logistic regression showed significant associations of the nocturnal mobile phone use with poor mental health, suicidal feelings, and self-injury after controlling for sleep length and other confounders. Conclusions Mobile phone use after lights out may be associated with poor mental health, suicidal feelings, and self-injury in both early and late adolescents. Association between reduced sleep and the mobile phone use was confined to early adolescents.

Introduction

Use of electronic devices such as mobile phones has become popular and prevalent among adolescents. In recent Japan, for example, 37.6% of junior high school students (grades 7–9) and 76.4% of high school students (grades 10–12) have their own mobile phones (Fukaya, 2002; Iwata, 2001). In the USA, 69% of 11- to 14-year olds and 85% of 15- to 18-year olds have their own mobile phones (Rideout, Foehr, & Roberts, 2010). Although mobile phones are mainly used in communication with peers (Iwata, 2001) and might assist social networking and maintaining close relations with the peers, studies have shown that mobile phone use may be associated with several health problems. For example, adolescents who use mobile phone in the morning reported a higher intensity of headache (Heinrich, Thomas, Heumann, von Kries, & Radon, 2010). Long-time mobile phone use causes neck–shoulder pain (Hakala, Rimpelä, SaarniA & Salminen, 2006) and waking-time tiredness (Punamäki, Wallenius, Nygård, Saarni, & Rimpelä, 2007). Adolescents who use mobile phone >15 min per day reported poorer perceived health (Söderqvist, Carlberg, & Hardell, 2008). Junior high school students who send more mobile phone e-mails more frequently experience depressive mood (Imamura et al., 2009). In adolescents, mobile phone dependency may be associated with suicidal tendencies (Yang, Yen, Ko, Cheng, & Yen, 2010).

Mobile phone use also causes sleep-related problems, including short sleep, subjective poor sleep quality, daytime sleepiness, and insomnia symptoms (Munezawa et al., 2011). In adolescents, bed time delays and length of sleep decreases with age (Sadeh, Dahl, Shahar, & Rosenblat-Stein, 2009), while adequate sleep is required to keep health and daytime functioning (Short et al., 2011). Several studies have suggested that sleep-related problems may significantly affect mental health in adolescents. Significant associations were observed between sleep disturbances and completed suicide in adolescents (Goldstein, Bridge, & Brent, 2008). Also, short sleep may be significantly associated with suicide attempts in adolescents. Sleep <8 hr was associated with suicide attempt in 1,362 Chinese adolescents (Liu, 2004). Sleep <6 hr may be associated with suicidal feelings and suicide attempt in 8,319 Taiwanese adolescents (Yen, King, & Tang, 2010).

According to these observations, we hypothesized that nocturnal mobile phone use, especially after lights out, may be associated with poor mental health, suicidal feelings, and self-injury in adolescents. If the nocturnal mobile phone use is associated with risk of suicidal feelings or self-injury, this risk might be reduced by a change in behavior through health education and other interventions. To our knowledge, no study has investigated the effect of the nocturnal mobile phone use on suicidal feelings and self-injury. We, therefore, conducted a cross-sectional survey of Japanese early adolescents (grades 7–9) and late adolescents (grades 10–12). We studied associations between nocturnal mobile phone use after lights out and suicidal feelings and self-injury, controlling for short sleep. To test the effect of sleep length on the associations, the relationship between the mobile phone use and sleep length was also examined.

Methods

Participants

Participants comprised junior high and high school students (7–12th grade) in Kochi Prefecture and Tsu City, Mie Prefecture, Japan. All 20 public junior high schools in Tsu City, 25 out of 118 public junior high schools, and 28 out of 36 public high schools in Kochi Prefecture participated in the survey. Of all students in those junior high and high schools (n = 19,436), 18,250 agreed to participate. Of the remainder, 798 were absent on the days of the survey and 388 declined to participate. Among the 18,250 students, 330 were excluded from the analysis because of incomplete answers to questions, regarding frequency of mobile phone use after lights out. Thus, 17,920 students (8,886 males and 9,034 females) were analyzed. We defined the “early adolescents” as seventh to ninth grade students and “late adolescents” as 10th to 12th grade students. According to the criteria, 8,520 early adolescents and 9,400 late adolescents participated in this study.

Study Design and Questionnaire

We conducted a cross-sectional survey of psychopathologies between 2008 and 2009. Students were requested to fill out a questionnaire regarding mental health status, behaviors, and lifestyle. Questions regarding mental health status included items from the 12-item version of the General Health Questionnaire (GHQ-12), length of sleep, suicidal feelings, and history of self-injury in the previous year.

GHQ is a self-report questionnaire for symptoms of anxiety or depression (Goldberg et al., 1976). The validity and reliability of the Japanese version of the GHQ-12 has been confirmed (Doi and Minowa, 2003; Fukunishi, 1990). The GHQ was validated for adolescents (Arakida et al., 2003; Kaneita et al., 2007). We used a four-point scale with binary score (0011) for each question. We defined participants whose total GHQ-12 score ≥ 4 as poor mental health, according to previous studies (Arakida et al., 2003; Kaneita et al., 2007). A previous study showed that the proportion of poor mental health was higher in female adolescents than in male adolescents and increased with school grade (Tait, French, & Hulse, 2003).

Suicidal feeling was measured by the following question: “Do you currently have thoughts that your life is no longer worth living?” (Paykel, Myers, Lindenthal, & Tanner, 1974). Possible answers were “No,” “Probably not,” “Possibly yes,” and “Yes.” When the answer was “Possibly yes” or “Yes,” the participant was regarded as having suicidal feelings.

In the questionnaire, self-harm behaviors in the previous 12 months were assessed using the following question: “Have you intentionally hurt yourself within the past year?” Respondents who answered “Yes” were also asked to provide a description of the actual act. Classification of the episodes as self-injury or otherwise was based on independent ratings by two raters using criteria described in a previous study (Hawton, Rodham, Evans, & Weatherall, 2002). The κ-value for agreement between the two raters was at 0.83 (95% CI 0.79–0.86). Any disagreement was resolved through discussion between the two raters and one external evaluator.

Frequency of mobile phone use after lights out was measured by the following question: “How often do you talk or send e-mails using a mobile phone after lights out recently?” Possible answers were “Never,” “Sometimes,” and “Almost every day.”

Length of sleep was measured by “How many hours and minutes do you regularly sleep at night recently?” The answers were classified into three categories in the analysis in reference to the former studies (Liu, 2004; Yen, et al., 2010): short sleep (<6 hr), average sleep (6–9 hr), and long sleep (>9 hr). Reports of drinking alcohol (within the past month) and use of recreational drugs (lifetime) were answered by “Yes” or “No.” Drinking alcohol (within the past month) and use of recreational drugs (lifetime) were also assessed, because several studies showed that substance use causes poor mental health in adolescents (Groth & Morrison-Beedy, 2011; Kubik, Lytle, Birnbaum, Murray, & Perry, 2003).

Ethical Aspects

The study was approved by the ethics committee of Mie University School of Medicine and Kochi Medical School. The principal investigators approached and asked the school principals to participate in the study. They explained that participation was voluntary, and if students, parents, or teachers did not agree, there was no need to participate. The principals then consulted with teachers and parents. With their agreement, teachers were given instructions regarding the method of distribution and collection of the questionnaires. The teachers distributed the questionnaire with an envelope to the students. Teachers explained that (1) participation was voluntary and anonymous and (2) the answered questionnaire would never be seen by teachers. When the students completed the questionnaire, they were instructed to put it in the envelope and seal it. Research staff collected the sealed questionnaires at each school. The answers were studied and analyzed anonymously.

Statistical Analysis

We performed all analyses by age group (e.g., early adolescents [grades 7–9] and late adolescents [grades 10–12]) First, demographic characteristics were summarized by sex and age groups. Missing data were excluded in each statistical analysis. The number of missing data for each variable is 52 for suicidal feelings, 372 for self-injury, 1,937 for length of sleep, 224 for drinking alcohol, and 103 for recreational drug use. To analyze the association between sleep length and nocturnal mobile phone use, the sleep length was compared using the frequency of mobile phone use after lights out with one-way ANOVA and post hoc Tukey by sex and age groups. The associations of mobile phone use after lights out with GHQ-12 score, suicidal feelings, and self-injury were studied using logistic regression. We calculated the odds ratios of poor mental health (GHQ ≥4), suicidal feelings, and self-injury for adolescents who used their mobile phones after lights out every day or sometimes (the reference was students group who did not use their mobile phones after lights out). Sex, age, alcohol, recreational drug use, and sleep length were controlled for in the calculation. Sleep length was treated as categorical data (<6, 6–9, and >9 hr).

The Statistical Package for the Social Sciences (SPSS) version 16.0 J for Windows (SPSS Inc., Tokyo, Japan) was employed in the statistical analyses. A nominal p < 0.05 was considered statistically significant.

Results

Early Adolescents

Preliminary Analyses

We summarized behaviors and mental status of participants in Table I. Female students more frequently used a mobile phone after lights out almost every day than did male students, X2 (1, N = 8,520) = 179.23, p < .001. Male students slept longer than did female students, t (7,668) = 10.11, p < .001. A one-way ANOVA was used to test for sleep length differences among three frequency of mobile-phone use. Sleep length differed significantly across the three frequencies, F (2, 4,056) = 51.15, p < .001 in male and F (2, 3,608) = 94.34, p < .001 in female early adolescents. Tukey post hoc comparisons of the three groups indicate that sleep length was significantly shorter in early adolescents when they more frequently used a mobile phone after lights out (Figure 1).

Figure 1.

Relationship between frequency of mobile phone use after lights out and length of sleep (n = 15,979). There were statistical significances (p < 0.001) between every combination of “never” mobile-phone use after lights out, “sometimes,” and “every day” with multiple comparisons (Tukey’s method) in both sexes of early adolescents. There were no statistical significances in late adolescents. EA = early adolescents; LA = late adolescents.

Figure 1.

Relationship between frequency of mobile phone use after lights out and length of sleep (n = 15,979). There were statistical significances (p < 0.001) between every combination of “never” mobile-phone use after lights out, “sometimes,” and “every day” with multiple comparisons (Tukey’s method) in both sexes of early adolescents. There were no statistical significances in late adolescents. EA = early adolescents; LA = late adolescents.

Table I.

Behaviors and Mental Health Status of Subjects

 Early Adolescents (7–9th)
 
Late Adolescents (10–12th)
 
 Male Female Total Male Female Total 
 N = 4,382 N = 4,138 N = 8,520 N = 4,504 N = 4,896 N = 9,400 
Age 13.7 ± 0.9 13.7 ± 0.9 13.7 ± 0.9 16.6 ± 0.9 16.6 ± 0.9 16.6 ± 0.9 
GHQ-12 score 2.5 ± 2.8 3.8 ± 3.2 3.2 ± 3.0 3.2 ± 3.0 4.6 ± 3.2 3.9 ± 3.2 
GHQ-12 ≥ 4, N (%) 1,228 (28.0) 2,007 (48.5) 3,235 (38.0) 1,707 (37.9) 2,937 (60.0) 4,644 (49.4) 
Suicidal feelings, N (%) 331 (7.6) 542 (13.1) 873 (10.3) 478 (10.7) 757 (15.5) 1235 (13.2) 
Self-injury (within 1 year), N (%) 46 (1.1) 228 (5.6) 274 (3.3) 65 (1.5) 331 (7.0) 396 (4.3) 
Length of sleep (hr) 7.6 ± 1.2 7.3 ± 1.3 7.4 ± 1.3 6.9 ± 1.3 6.6 ± 1.2 6.7 ± 1.3 
Drinking alcohol, N (%) 435 (10.0) 442 (10.8) 877 (10.4) 699 (15.7) 822 (17.1) 1,521 (16.4) 
Usage of recreational drug, N (%) 42 (1.0) 25 (0.6) 67 (0.8) 39 (0.9) 16 (0.3) 55 (0.6) 
Mobile phone use after lights out, N (%)       
    Never 3,365 (76.8) 2,474 (59.8) 5,839 (68.5) 2,290 (50.8) 1,754 (35.8) 4,044 (43.0) 
    Sometimes 623 (14.2) 877 (21.2) 1,500 (17.6) 1,176 (26.1) 1,322 (27.0) 2,498 (26.6) 
    Every day 394 (9.0) 787 (19.0) 1,181 (13.9) 1,038 (23.0) 1,820 (37.2) 2,858 (30.4) 
 Early Adolescents (7–9th)
 
Late Adolescents (10–12th)
 
 Male Female Total Male Female Total 
 N = 4,382 N = 4,138 N = 8,520 N = 4,504 N = 4,896 N = 9,400 
Age 13.7 ± 0.9 13.7 ± 0.9 13.7 ± 0.9 16.6 ± 0.9 16.6 ± 0.9 16.6 ± 0.9 
GHQ-12 score 2.5 ± 2.8 3.8 ± 3.2 3.2 ± 3.0 3.2 ± 3.0 4.6 ± 3.2 3.9 ± 3.2 
GHQ-12 ≥ 4, N (%) 1,228 (28.0) 2,007 (48.5) 3,235 (38.0) 1,707 (37.9) 2,937 (60.0) 4,644 (49.4) 
Suicidal feelings, N (%) 331 (7.6) 542 (13.1) 873 (10.3) 478 (10.7) 757 (15.5) 1235 (13.2) 
Self-injury (within 1 year), N (%) 46 (1.1) 228 (5.6) 274 (3.3) 65 (1.5) 331 (7.0) 396 (4.3) 
Length of sleep (hr) 7.6 ± 1.2 7.3 ± 1.3 7.4 ± 1.3 6.9 ± 1.3 6.6 ± 1.2 6.7 ± 1.3 
Drinking alcohol, N (%) 435 (10.0) 442 (10.8) 877 (10.4) 699 (15.7) 822 (17.1) 1,521 (16.4) 
Usage of recreational drug, N (%) 42 (1.0) 25 (0.6) 67 (0.8) 39 (0.9) 16 (0.3) 55 (0.6) 
Mobile phone use after lights out, N (%)       
    Never 3,365 (76.8) 2,474 (59.8) 5,839 (68.5) 2,290 (50.8) 1,754 (35.8) 4,044 (43.0) 
    Sometimes 623 (14.2) 877 (21.2) 1,500 (17.6) 1,176 (26.1) 1,322 (27.0) 2,498 (26.6) 
    Every day 394 (9.0) 787 (19.0) 1,181 (13.9) 1,038 (23.0) 1,820 (37.2) 2,858 (30.4) 

Note. The number of the subjects and percentage are described in each column. Column of age, GHQ-12 score, and length of sleep shows M ± SD. GHQ-12 = 12-item General Health Questionnaire.

The female students had higher GHQ-12 score than male students, t (8,518) = 20.95, p < .001. Prevalence rates of suicidal feelings and self-injury were higher in female than in male, X2 (1, N = 8,494) = 71.34, p < .001, and X2 (1, N = 8,357) = 136.38, p < .001, respectively.

Primary Analyses

Associations of poor mental health, suicidal feelings, and self-injury with mobile phone use are summarized in Table II. Logistic regression showed that mobile phone use after lights out was significantly associated with poor mental health (GHQ-12), suicidal feelings, and self-injury, after adjusting for sex, age, alcohol, drug use, and sleep length in early adolescents.

Table II.

Relationships Between Mobile Phone Use After Lights Out and Poor Mental Health, Suicidal Feelings, and Self-Injury in Early and Late Adolescents

 Early Adolescents (7–9th)
 
Late Adolescents (10–12th)
 
 Unadjusted OR Adjusted OR Unadjusted OR Adjusted OR 
Poor mental health     
MPU sometimes 1.58*** (1.41–1.78) 1.34*** (1.18–1.52) 1.25*** (1.13–1.39) 1.15* (1.03–1.28) 
MPU every day 2.38*** (2.09–2.70) 1.65*** (1.43–1.92) 1.88*** (1.71–2.07) 1.54*** (1.38–1.72) 
Suicidal feelings     
MPU sometimes 1.13 (0.93–1.37) 0.98 (0.79–1.22) 1.02 (0.88–1.19) 0.96 (0.81–1.13) 
MPU every day 2.37*** (1.99–2.82) 1.62*** (1.31–1.99) 1.46*** (1.27–1.68) 1.22* (1.04–1.42) 
Self-injury     
MPU sometimes 1.01 (0.71–1.45) 0.78 (0.53–1.16) 1.33* (1.00–1.77) 1.21 (0.89–1.64) 
MPU every day 3.26*** (2.48–4.27) 1.56** (1.12–2.17) 2.62*** (2.07–3.33) 1.75*** (1.33–2.29) 
 Early Adolescents (7–9th)
 
Late Adolescents (10–12th)
 
 Unadjusted OR Adjusted OR Unadjusted OR Adjusted OR 
Poor mental health     
MPU sometimes 1.58*** (1.41–1.78) 1.34*** (1.18–1.52) 1.25*** (1.13–1.39) 1.15* (1.03–1.28) 
MPU every day 2.38*** (2.09–2.70) 1.65*** (1.43–1.92) 1.88*** (1.71–2.07) 1.54*** (1.38–1.72) 
Suicidal feelings     
MPU sometimes 1.13 (0.93–1.37) 0.98 (0.79–1.22) 1.02 (0.88–1.19) 0.96 (0.81–1.13) 
MPU every day 2.37*** (1.99–2.82) 1.62*** (1.31–1.99) 1.46*** (1.27–1.68) 1.22* (1.04–1.42) 
Self-injury     
MPU sometimes 1.01 (0.71–1.45) 0.78 (0.53–1.16) 1.33* (1.00–1.77) 1.21 (0.89–1.64) 
MPU every day 3.26*** (2.48–4.27) 1.56** (1.12–2.17) 2.62*** (2.07–3.33) 1.75*** (1.33–2.29) 

Note. Missing data were excluded in each statistical analysis. Odds ratios were calculated by logistic regression analysis. Using mobile phone after lights out sometimes and every day were compared to no use (reference). 95% confidence intervals are shown in parentheses. Odds ratios were adjusted for sex, age, drinking alcohol, recreational-drug use, and sleep length. MPU = mobile-phone use.

*p < .05, **p < .01, ***p < .001.

Early adolescents who reported that they used their mobile phones after lights out “almost every day” were more likely to have poor mental health, compared to those who did not use their mobile phones after lights out (OR = 1.65; 95% CI 1.43–1.92; p < .001). Logistic regression also showed the association between nocturnal mobile phone use “almost every day” to suicidal feelings after controlling for sex, age, alcohol, drug use, and sleep length (OR = 1.62; 95% CI 1.31–1.99; p < .001). Early adolescents who used their mobile phones “almost every day” were more likely to experience self-injury after controlling for sex, age, alcohol, drug use, and sleep length, compared to those who did not use their mobile phones after lights out (OR = 1.56; 95% CI 1.12–2.17; p = .009).

Late Adolescents

Preliminary Analyses

Similar to the early adolescents, female students more frequently used a mobile phone after lights out almost every day than did male students, X2 (1, N = 9,400) = 221.26, p < .001. Male students slept longer than did female students, t (8,311) = 8.22, p < .001. However, not similar to the early adolescents, the relationship between sleep length and nocturnal mobile phone use was not significant in late adolescents, F (2, 4,093) = 1.646, p = .193 in male and F (2, 4,214) = 0.843, p = .430 in female (Figure 1).

The female students had higher GHQ-12 score than male students, t (9398) = 23.01, p < .001, similar to the early adolescents. Prevalence rates of suicidal feelings and self-injury were higher in female than in male, X2 (1, N = 9,374) = 48.74, p < .001, and X2 (1, N = 9,191) = 167.57, p < .001, respectively.

Primary Analyses

Logistic regression showed that mobile phone use after lights out was significantly associated with poor mental health (GHQ-12), suicidal feelings, and self-injury, after adjusting for sex, age, alcohol, drug use, and sleep length in late adolescents.

The GHQ-12 score was significantly associated with mobile phone use after controlling for sex, age, alcohol, drug use, and sleep length. Compared to late adolescents who reported that they did not use their mobile phones after lights out, those who used their mobile phones “almost every day” were more likely to have poor mental health (OR = 1.54; 95% CI 1.38–1.72; p < .001). Logistic regression also showed the association between nocturnal mobile phone use “almost every day” to suicidal feelings after controlling for sex, age, alcohol, drug use, and sleep length (OR = 1.22; 95% CI 1.04–1.42; p = .014). Late adolescents who used their mobile phones after lights out “almost every day” were more likely to experience self-injury after controlling for sex, age, alcohol, drug use, and sleep length, compared to those who did not use their mobile phones after lights out (OR = 1.75; 95% CI 1.33–2.29; p < .001).

Discussion

The present study investigated the association of nocturnal mobile-phone use with suicidal feelings and self-injury in adolescents. Mobile phone use after lights out was associated with poor mental health, suicidal feelings, and self-harm in both early and late adolescents. The association remained statistically significant after controlling for sleep length. To our knowledge, this is the first study to observe an association of nocturnal mobile phone use with suicidal feelings and self-injury. Mobile phone use after lights out could be a target in health education and interventions to improve mental health and to reduce suicidal feelings and self-injury in adolescents.

Frequent mobile phone use after lights out was significantly associated with short sleep in early adolescents. In late adolescents, in contrast, the mobile phone use was not significantly associated with short sleep. Previous studies observed associations between short sleep and suicide feelings or suicide attempts in adolescents (Liu, 2004; Yen et al., 2010). The reduction of sleep length might play a role in the increase of the risk in early adolescents who frequently use mobile phone after lights out.

The ORs of poor mental health, suicidal feelings, and self-harm, however, remained significant after controlling for sleep length in both early and late adolescents, as summarized in Table II. The nocturnal mobile phone use might be associated with the risks, even when it does not reduce the length of sleep. A mechanism of the association might be worsening of the quality of sleep. While we do not have data to support this premise in the present study, looking at the bright display of mobile phone might have critical physiological effects on sleep. The combination of looking at a bright display and doing an exciting task (e.g., playing a shooting game) may change the secretion of melatonin and therefore the quality of sleep (Higuchi, Motohashi, Liu, Ahara, & Kaneko, 2003). A previous study reported that the electromagnetic field, not only bright light, emitted from mobile phones could have an effect on nocturnal melatonin secretion (Jarupat, Kawabata, Tokura, & Borkiewicz, 2003).

Another mechanism could be negative emotions or stress by the mobile phone use. Students might experience negative emotions when talking or exchanging e-mails with their friends just before going to sleep. A previous study found that 16.5% of junior high students experienced stress during e-mail exchange using a mobile phone (Imamura et al., 2009). Another study reported that being worried about not receiving e-mail replies may be related to worsened mental health, including suicidal feelings, in adolescents (Katsumata, Matsumoto, Kitani, & Takeshima, 2008). Bullying might also play a role. A previous study observed that cyber bullying using a mobile phone can increase the risk of suicide in early teens (Brunstein Klomek, Sourander, & Gould, 2010).

The present study indicates that the mobile phone use might make a focus of the psychological education to improve mental health in adolescents. Possession of mobile phone is highly prevalent, and a previous study observed that its use might help communication with peers in adolescence (Kamibeppu & Sugiura, 2005). Prohibition of its possession or use may not be executable in this age group. However, focusing on change in nocturnal use might be feasible, for example, through health education in high schools.

Limitations and Future Research

The following limitations are acknowledged in the present study. First, this is a cross-sectional study, and therefore a causal relationship was not clear when a significant association was observed. Longitudinal follow-up studies may be required. Second, we asked the experiences of self-injury within a year, not at present, while we asked recent status of mobile phone use and sleep length. The timeframes might not be very consistent in the examination of their association. Third, we used a self-report questionnaire. Self-report of sleep could be inaccurate. The information regarding current mental health as well as mobile phone use might also be less reliable than interview-based surveys. Fourth, participants with missing data for length of sleep were larger than other variables. This may partly be due to the style of the question. We asked the students to fill the blanks as “__ hours__ minutes” and many students did not fill the minutes. Fifth, we did not have information about the difference between weekday and weekend sleep, which could be associated with psychological health (Kim et al., 2011). Sixth, we were not able to access and follow the students who might be with poor mental health or suicidal feelings, because the questions were anonymously answered. This is a methodological limitation of the study. Finally, a small number of the students were absent from the study. If a portion of them were absent due to poor mental health or had difficulty getting up in the morning because of, for example, sitting up late talking or sending e-mails, their exclusion might have affected the results.

Funding

This study was supported by a Grant from the Ministry of Health, Labour and Welfare of Japan (#H19-kokoro-ippan-012) and Grant-in-aid from the Research Group for Schizophrenia in Japan (Atsushi Nishida). Dr Nishida also acknowledges support from the Research Group for Schizophrenia in Japan, Award for Research Excellence.

Conflicts of interest: None declared.

Acknowledgment

Norihito Oshima and Atsushi Nishida contributed equally to this work.

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