Self-injury in Japanese junior and senior high-school students: Prevalence and association with substance use
Toshihiko Matsumoto, MD, PhD, Center for Suicide Prevention, National Institute of Mental Health, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8553, Japan. Email: firstname.lastname@example.org
The present study examined the prevalence of self-injury and its association with substance abuse in 2974 junior and senior high-school students, by self-reporting questionnaires. Consequently, 9.9% of students (boys, 7.5%; girls, 12.1%) reported an experience of self-injury at least once. Significant differences were found in substance use-related problems including alcohol abuse, smoking, and illicit drug use (P < 0.001) between students with and without an experience of self-injury. The results also suggest that self-injuring students may more easily gain access to illicit drugs even if they had not yet experienced the use of illicit drugs. Self-injury in adolescence may be associated with substance use and is considered to be a risk factor predicting future illicit drug use.
NON-FATAL SELF-INJURY AND substance abuse have common features with regard to coping strategy for reducing unpleasant moods,1 while self-injury is considered a risk factor leading to suicidal behavior in the future.2 These deliberate self-harm behaviors frequently coexist,3,4 and each of them is one of the most important mental health problems in adolescence.5,6
However, in Japan epidemiological findings on the prevalence of self-injury in adolescence are not common, while the prevalence of substance abuse in junior high-school students has been investigated nationwide.7 Although we previously reported on the prevalence of self-injury, and the association with substance use such as smoking and drinking in Japanese high-school students,5,6 each of these findings was obtained from only one public coeducational school5 or private girls' school.6
The purpose of the present study was to clarify the prevalence of self-injury including wrist-cutting, which means cutting one's own body, and to confirm the association between self-injury and substance use in junior and senior high-school students, using a relatively large sample collected from many schools having a wide range of year levels.
The subjects were 2974 junior and senior high-school students (1459 boys and 1515 girls; mean age ± SD, 14.7 ± 1.4 years), who consented to participate in the present study. They constituted 97.2% of the targeted sample of 3058 students of 12 coeducational schools; six public junior high schools, and five public and one private senior high schools, all of which are located in the suburban areas of Kanagawa and Saitama Prefectures. According to the ratio of the graduates going to university the previous year, the academic grades of the six senior high schools were considered to consist of one high (>90%), three moderate (50–90%), and two low (<50%). Each of these junior and senior high schools invited the first author to give the lecture on preventing drug abuse, which has been recently held nationwide in high schools, from 2005 to 2006. This study was approved by the principal and the Parents and Teachers Association of each school, and written informed consent was obtained from all participants.
We administered a self-reporting questionnaire originally designed to evaluate lifetime experiences of deliberate self-injury, smoking, and drug-related problems. Question 1 (experience of self-injury): ‘Have you ever injured yourself deliberately with a knife or other sharp material?’; question 2 (experience of smoking): ‘Have you ever smoked?’; question 3 (friends or acquaintances using illicit drugs): ‘Do you have any friends or acquaintances using illicit drugs?’; question 4 (experienced temptations to use illicit drugs): ‘Have you ever been tempted to use illicit drugs?’; and question 5 (experience of illicit drug use): ‘Have you ever experienced the use of illicit drugs?’. All questions were answered ‘yes’ or ‘no’, except question 2, which was answered ‘never experienced’, ‘past experience’, or ‘currently smoking’. The Quantity and Frequency Scale (QFS) also was administered. The QFS is an established, self-reporting instrument for screening alcohol abuse in adolescence and consists of two items.8 Suzuki et al. demonstrated that a QFS score ≥4 points suggests an existence of alcohol abuse in Japanese adolescents.8
These self-reporting questionnaires were administered after the lecture on drug abuse prevention. Completed and unsigned questionnaires were immediately collected by the first author. All statistical analyses were performed using SPSS for Windows (version 12.0, SPSS, Chicago, IL, USA). Student's t-test was used for continuous data and χ2 analysis for categorical data to compare drinking, smoking, and drug-related problems between students with and without an experience of self-injury. The significance level was set at P < 0.001, and all P were two-tailed.
A total of 293 students (9.9%), consisting of 108 boys (7.5%) and 185 girls (12.1%), reported an experience of self-injury at least once. Table 1 compares drinking, smoking, and drug-related problems between students with and without an experience of self-injury. The students with an experience of self-injury (SI group) significantly included fewer boys than those without (non-SI group), but no significant differences were found in mean ages between the two groups.
Table 1. Student substance problems
|Age (years)||14.5 ± 1.4||14.7 ± 1.4||2.128||2972|
|QFS ≥ 4 (problematic drinking) (%)||8.7||1.2||74.483*||1|
|Experience of smoking* (%)|
| Never experienced||66.7||88.5||129.203*||2|
| Past experience||24.3||10.1|| || |
| Currently smoking||9.0||1.4|| || |
|Drug-related problems (%)|
| Existence of friends or acquaintances using illicit drugs||19.9||5.3||88.547*||1|
| Experiencing temptations to use illicit drugs||5.8||1.2||34.681*||1|
| Experiencing use of illicit drugs||3.8||0.1||82.181*||1|
Significant differences were found in the variables related to substance use between the SI and non-SI groups. The SI group more frequently scored >4 points on the QFS and more frequently reported past and current experiences of smoking than the non-SI group. The SI group also more frequently reported having friends or acquaintances using illicit drugs, experiencing temptations to use illicit drugs, and experiencing the use of illicit drugs than the non-SI group did.
To our knowledge this is the first Japanese study to examine the prevalence of self-injury in junior and senior high-school students, using a relatively large sample collected in a multischool setting.
The present study clarified that 9.9% of junior and senior high-school students (male, 7.5%; female, 12.1%) reported a lifetime experience of deliberate self-injury at least once. These findings confirm our previous studies using a small sample, which reported that the prevalence of self-injury in male and female junior high-school students was 8.0% and 9.3%5 and that 14.3% of female senior high-school students reported self-cutting at least once.6 The present results also appear to be approximately consistent to the prevalence of self-injury in other countries: 11.2% of female high-school students in the UK,9 12% of female university students in the USA,10 13.9% of Canadian adolescents,11 although only Turkish high-school students had a higher prevalence of self-injury (21.4%).12
The results demonstrate that self-injury may be positively associated with the use of substances including tobacco and alcohol, which are well known to be risk factors predicting future illicit drug use.7,8 These findings confirm our previous findings.5,6 The present study also demonstrates that self-injury may be positively associated with illicit drug use and indicates that the self-injuring students may more easily gain access to illicit drugs, even if they had not previously used them, because they more frequently reported having friends or acquaintances who use illicit drugs, and that they themselves experienced a temptation to use them.
These findings suggest that self-injury in students, as well as alcohol abuse and smoking, may be a risk factor predicting future illicit drug use. Also involved is the possibility that substance abuse in adolescents may imply deliberate self-destruction similar to self-injury, as Walsh described.1 Therefore when educating students to prevent drug abuse, teachers should understand that emphasizing only the harmful aspects may be insufficient.
The present study suffered from three limitations. First, a sample representation may be biased, because all 12 participating schools invited the first author to give the lecture on prevention of drug abuse. Second, the influences of the lecture cannot be excluded because this investigation was performed after the lecture. Last, data were acquired via self-reporting questionnaires rather than by a semi-structured interview or a collection of collateral information, although Hawton et al. noted that anonymous self-reporting questionnaire is the best way to investigate self-harming behavior in adolescents.13 Despite these limitations, this is the largest sample study on the prevalence of self-injury in adolescence in Japan.