Journal of Adolescent Health xxx (2017) 1e5

www.jahonline.org
Original article

Preference for Solitude, Social Isolation, Suicidal Ideation, andSelf-Harm in Adolescents
Kaori Endo, Ph.D. a, Shuntaro Ando, M.D., Ph.D. a, b,1, Shinji Shimodera, M.D., Ph.D. c, *,Syudo Yamasaki, Ph.D. a, Satoshi Usami, Ph.D. d, Yuji Okazaki, M.D., Ph.D. e, f,
Tsukasa Sasaki, M.D., Ph.D. g, Marcus Richards, Ph.D. h, Stephani Hatch, Ph.D. i, andAtsushi Nishida, Ph.D. aaDepartment of Psychiatry and Behavioural Science, Tokyo Metropolitan Institute of Medical Science, Setagaya-ku, Tokyo, Japan
Department of Neuropsychiatry, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, Japanc
Department of Neuropsychiatry, Kochi Medical School, Kochi University, Nankoku-shi, Kochi, Japand
Department of Psychology, University of Tsukuba, Tsukuba, Ibaraki, Japane
Kouseikai Michinoo Hospital, Nagasaki-shi, Nagasaki, Japanf
Tokyo Metropolitan Matsuzawa Hospital, Setagaya-ku, Tokyo, Japang
Department of Physical and Health Education, Graduate School of Education, The University of Tokyo, Bunkyo-ku, Tokyo, Japanh
MRC Unit for Lifelong Health and Aging, University College London, London, United Kingdomi
Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, United Kingdomb

Article history: Received November 9, 2016; Accepted February 22, 2017
Keywords: Preference for solitude; Social isolation; Suicidal ideation; Self-harm; Adolescence

A B S T R A C T

Purpose: Social isolation is associated with suicidal ideation (SI) and self-harm (SH) among
adolescents. However, the association between preference for solitude (PfS), SI, and SH is
unknown. The prevalence of adolescents who have both of PfS and social isolation and the risks for
SI and SH among them are also unknown.
Methods: Information on PfS, social isolation, SI, and SH was collected in a large-scale
school-based survey on adolescents, using a self-report questionnaire. Associations between
PfS, SI, and SH were examined by logistic regression analysis. The interactions between PfS
and social isolation on SI and SH were also investigated. The odds of SI and SH were examinedfor groups deﬁned by presence of PfS and social isolation.
Results: Responses from 17,437 students (89.3% of relevant classes) were available. After adjustingfor demographic characteristics and social isolation, PfS was associated with increased odds of SI(odds ratio [OR] ¼ 3.1) and SH (OR ¼ 1.9). There was no interaction between PfS and social isolation
on SI and SH. After adjusting for demographic characteristics, the odds for SI (OR ¼ 8.6) and SH(OR ¼ 3.8) were highest among adolescents with both PfS and social isolation (8.4% of all
respondents).

IMPLICATIONS AND
CONTRIBUTION

Adolescents with a preference for solitude, particularly those who are socially
isolated, are at increased
risk of suicidal ideationand self-harm. These results suggest focusing suicide prevention efforts on
those who say they prefersolitude and have noone to consult with about
worries or troubles.

Conﬂicts of Interest: The authors have no conﬂicts of interest to disclose.
Clinical trials registry site and number: none.
* Address correspondence to: Shinji Shimodera, M.D., Ph.D., Department of Neuropsychiatry, Kochi Medical School, Kochi University, Oko-cho Kohasu, Nankoku-shi,
Kochi 783-8505, Japan.
E-mail address: shimodes@kochi-u.ac.jp (S. Shimodera).
1
Equal contribution to ﬁrst author.
1054-139X/Ó 2017 Society for Adolescent Health and Medicine. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
http://dx.doi.org/10.1016/j.jadohealth.2017.02.018

2K. Endo et al. / Journal of Adolescent Health xxx (2017) 1e5

Conclusions: PfS was associated with increased odds of SI and SH in adolescents. No interaction
effect between PfS and social isolation on SI and SH was found, but adolescents with PfS and social
isolation had the highest risk for SI and SH. Parents and professionals should pay attention tosuicide risk in adolescents with PfS.
Ó 2017 Society for Adolescent Health and Medicine. Published by Elsevier Inc. This is an open
access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Suicide is the second leading cause of death in young people,
accounting for 8.5% of total deaths in young people [1]. In Japan,
the leading cause of death among 15- to 39-year-olds is suicide,
while road trafﬁc accidents is the leading cause in many otherdeveloped countries [2]. Also, self-inﬂicted injury is one of theleading causes of disability-adjusted life years in young people[3]. Social isolation has been identiﬁed as a risk factor for suicidal
problems [1,4]. Since a rapidly changing social world increases
the likelihood of social isolation during adolescence [5], more
attention should be paid for adolescents who experience social
isolation.
Preference for solitude (PfS) in adolescence can be regarded
as a developmental process. PfS has been said as a broad
construct of unsociability and avoidance [6] and motivated by
low approach and low-to-high avoidance [7]. The desire forsolitude increases during adolescence, and time spent alone inadolescence can sometimes be beneﬁcial for adjustment,
perhaps because solitude facilitates individuation or identity
formation [8]. As children grow older, solitude becomes more
acceptable and they report solitude as more positive andimportant [8e10]. It has also been suggested that spending timealone in a volitional and autonomous manner is associated withhigher levels of well-being [11]. On the other hand, negative
aspects of PfS have also been reported. Several studies showedthat PfS in early adolescence is associated with peer difﬁculties
and maltreatment [12e14] and, in adolescence more generally,
with low self-esteem, anxiety/depression, and emotional dysregulation [6,7]. Therefore, it is possible that risk for suicidal
ideation (SI) and self-harm (SH) is increased in adolescents with
PfS.
However, to the best of our knowledge, this has not been
investigated. Furthermore, no studies have examined the prevalence of adolescents who had both PfS and social isolation andthe risk of SI and SH among them. The objective of this study
therefore was to examine these possible associations.

Parents were informed of the research project by letter andasked to notify the school if they did not want their children toparticipate. On the day of the survey, students were told thatparticipation was voluntary and there was no disadvantage in
nonparticipation; they were then given the choice of opting out.
Each teacher reported the total number of students present andabsent on the day of the survey. The study was approved by the
ethics committees of Tokyo Metropolitan Institute of Medical
Science, Mie University School of Medicine, and Kochi Medical
School.
Among 19,436 students in the relevant classes, 18,250 (93.8%)
agreed to participate. Of the remainder, 798 (4.1%) were absent
on the day of the survey and 388 (2.0%) declined to participate.
Among the participants, 903 (4.9%) were excluded from theanalysis because of incomplete answers to questions (numbers of
missing data for PfS was 155, for social isolation was 267, for SI
was 95, and for SH was 433). Thus, responses from 17,347 (95.1%)
students were analyzed (89.3% of all students in the relevant
classes). Of these students, 50.2% were female, and their ages
ranged from 12 to 18 years, with a mean age of 15.2 years(standard deviation ¼ 1.7 years).
Measurements
The participants were asked to ﬁll in an anonymous selfreport questionnaire including questions about PfS, social isolation, SI, SH, and demographic characteristics including age, sex,
and living status.
Preference for solitude

Methods

The question, “Do you prefer to be alone rather than to bewith someone?” was used to evaluate PfS. This question had thehighest loading among the four items for measuring PfS in theprevious study [6]. The four possible responses were “no,”“probably no,” “probably yes,” and “yes.” Students who replied“yes” or “probably yes” were deﬁned as those who had PfS.

Study design

Social isolation

The present study was a cross-sectional survey of students inpublic junior and senior high schools (7the12th graders, age
range 12e18 years). The survey was conducted between 2008
and 2009 using a self-report questionnaire. The principal
investigator of the study asked all heads and administrators of
public junior high schools in the city of Tsu, (the second biggest
city in a rural prefecture, having about 290,000 people),and public junior and senior high schools in Kochi Prefecture,(a rural prefecture, having approximately 780,000 people),to participate into the survey. Of the 138 junior and 36 seniorhigh schools invited, 47 junior and 30 senior high schools
participated.

In this article, considering the previous studies [15], wedeﬁned social isolation as the lack of quantity of social contacts
for emotional support. The question “With how many people can
you consult about your worries or troubles?” was used. The ﬁve
possible responses were “no one,” “one,” “two,” “three,” and“more than four.” Individuals who answered “no one” weredeﬁned as those who were socially isolated.
Suicidal ideation
Current SI was assessed by the question “Do you currently
have thoughts that your life is no longer worth living?” The fourK. Endo et al. / Journal of Adolescent Health xxx (2017) 1e5

3

possible responses were “no,” “probably no,” “probably yes,” and“yes.” Responses of “yes” or “probably yes” were regarded as thepresence of current suicidal feelings.

isolationþ; Figure 1). Risk for SI and SH in these four groups wasinvestigated using multivariable logistic regression analysis.

Self-harm

Results

The question “Have you intentionally hurt yourself within thepast year?” was used to measure the 12-month prevalence of SH.
The two possible responses were “no” and “yes.” Based on thedeﬁnition used in a previous study [16] and in a comparative
study of seven countries [17], SH was deﬁned as an act with anonfatal outcome in which an individual deliberately did one ormore of the following: initiated behavior (e.g., self-cutting andjumping from a height) which was intended to cause SH;
ingested a substance in excess of the prescribed or generally
recognized therapeutic dose; or ingested a substance or object
not intended for ingestion. Classiﬁcation of the episode as SH orotherwise was based on independent ratings by two researchers
using these criteria. The kappa value for agreement between thetwo raters was .83 (95% conﬁdence interval [CI]: .79e.86). Anyclassiﬁcation discrepancies between the two raters wereresolved by discussion.

Seventeen thousand three hundred forty-seven adolescentswere included in this study. The mean age was 15.2 (standard
deviation ¼ 1.7), and the prevalence of PfS and social isolation
were 29.9% and 17.2%, respectively. The prevalence of current SI
and 12-month prevalence of SH were 11.5% and 3.8%, respectively. The prevalence of PfS increased with age (p < .01, Table 1).
The prevalence of social isolation increased with age in boys
(p < .01).
PfS was associated with increased odds of SI (odds ratio[OR] ¼ 3.7, 95% CI: 3.4e4.1, p < .001, Table 2). Adjusting for demographic characteristics and social isolation slightly attenuatedthis association although it remained signiﬁcant at the 5% level(adjusted OR ¼ 3.1, 95% CI: 2.8e3.4, p < .001). Similarly, PfS was
associated with the increased odds of SH (OR ¼ 2.2, 95% CI:
1.9e2.6, p < .001). This association was also slightly attenuatedby adjusting for demographic characteristics and social isolation,although again it remained signiﬁcant at the 5% level (adjusted
OR ¼ 1.9, 95% CI: 1.6e2.3, p < .001). There was no statisticallysigniﬁcant interaction effect at the 5% level between PfS andsocial isolation on SI (p ¼ .70) and SH (p ¼ .06). Linear regression
analyses in which PfS and SI were treated as ordinal variables
showed that students with stronger PfS had stronger SI(adjusted: B ¼ .263, p < .001). The sensitivity analysis in which
PfS was treated as an ordinal categorical variable in logistic
regression analyses showed that stronger PfS was associatedwith the increased odds of SH (adjusted OR ¼ 1.401, p < .001).
More students with PfS experienced social isolation thanthose without PfS (28.1% vs. 12.6%, p < .001). Logistic regression
analysis showed that odds of SI were higher in group 2, 3, andStatistical analysis
Associations between PfS, SI, and SH were investigated using
logistic regression analysis. Multivariable logistic regression
analysis was conducted to control for the effects of demographic
characteristics and social isolation. A possible interaction effectbetween PfS and social isolation on SI and SH was also tested.
Linear regression analysis treating PfS, SI, and SH as ordinalvariables was also conducted. Next, students were divided into
four groups according to the presence of PfS and social isolation(group 1: PfS/social isolation, group 2: PfS/social isolationþ,group 3: PfSþ/social isolation, and group 4: PfSþ/social

Preference for solitude

Social isolation

Notsocially isolated
Not
prefer for solituden = 10628(61.3%)

Group 1n = 12159(70.1%)
Socially isolated
n = 1531(8.8%)

Group 2

Total sample
n = 17347 (100.0%)
Notsocially isolated
n = 3732(21.5%)

Group 3Prefer for solituden = 5188(29.9%)
Socially isolated
n = 1456(8.4%)

Group 4

Figure 1. Distribution of four groups deﬁned by the presence of preference for solitude and social isolation.

4

K. Endo et al. / Journal of Adolescent Health xxx (2017) 1e5

Table 1
Prevalence of preference for solitude and social isolation in different age and sex groups
Sex

Age

N

PfS, n (%)

p value

Social isolation, n (%)

p value

Boys

12
13
14
15
16
17
18

360
1,458
1,478
1,474
1,594
1,409
869

76 (21.1%)
333 (22.8%)392 (26.5%)
413 (28.0%)
531 (33.3%)
471 (33.4%)
310 (35.7%)<.001a (for age difference)69 (19.2%)
298 (20.4%)358 (24.2%)
333 (22.6%)
365 (22.9%)339 (24.1%)
229 (26.4%).001a (for age difference)

Girls

12
13
14
15
16
17
18

326
1,358
1,404
1,472
1,694
1,559
892

69 (21.2%)
350 (25.8%)388 (27.6%)
442 (30.0%)554 (32.7%)
549 (35.2%)
310 (34.8%).052 (for sex difference)<.001a (for age difference)<.001 (for sex difference).977a (for age difference)

41 (12.6%)
160 (11.8%)
148 (10.5%)160 (10.9%)205 (12.1%)
188 (12.1%)
94 (10.5%)

PfS ¼ preference for solitude.
ap value for chi-square for trend.

4 compared with group 1 (all p < .01; Table 3). Multivariablelogistic regression analysis adjusting for demographic characteristics showed similar results. The odds of SI were highest ingroup 4 and were 8.6 times higher than that of in group 1. Similar
results were observed with regard to the risk for SH. For multivariable logistic regression analysis adjusting for demographic
characteristics, the odds of SH was higher in group 3 and 4compared with group 1 (p < .001, Table 3). The odds of SH werehighest in group 4 and were 3.8 times higher in group 4 than thatof in group 1.
Discussion
This was the ﬁrst study to investigate risk of suicidal problems
among adolescents who had PfS and were socially isolated. PfS
was associated with increased risk of SI and SH. Furthermore, PfS
and social isolation had no interactive effect on SI and SH, andadolescents with PfS and social isolation were at the highest risk
for SI and SH.
The prevalence of PfS and social isolation increased withadolescent age. This may reﬂect the fact that solitude becomes
more normative in late adolescence than in early adolescence [9].
The association between PfS and social isolation was consistent
with a previous ﬁnding that a positive correlation between peer
loneliness and positive attitude to solitude exists. [18].
PfS was associated with increased odds of SI and SH of adolescents. This is consistent with previous studies showing thatadolescents with PfS had more depressive symptoms than those
without [9,10]. Adolescents with PfS may internalize negative
peer views on withdrawal, which is especially strong in earlyadolescence [12], leading to SI and SH. Also, since the quality ofpeer relationships affects psychological well-being in adolescence [4], adolescents with PfS may tend to feel alienated andsuicidal if not belonging to peer groups.
Furthermore, PfS and social isolation had no interactive effecton SI and SH, and PfS did not mitigate the effect of social isolation
on SI and SH. Adolescents with PfS and social isolation had thehighest odds of SI and SH. This result does not seem to accord
with a previous ﬁnding that higher levels of well-being wereassociated with spending time alone in a volitional and autonomous manner [8]. However, PfS may not always be volitional
and autonomous and may arise from lack of social contact. Theremay be many adolescents who might try to rationalize that they
prefer solitude, even if they feel lonely and uncomfortable with
their isolated state. PfS may be a complicated construct rather
than a simple one. Solitude facilitates individuation or identity
formation [8] and is associated with higher levels of well-being[11]. On the other hand, PfS is associated with peer difﬁculties
and maltreatment [12e14], low self-esteem, anxiety/depression,and emotional dysregulation [6,7].
The main strength of this study was the large sample and thehigh response rate. On the other hand, there were several limitations. First, the sample consisted of participants who were inattendance at school on the day of the survey. Second, the data
were cross-sectional, and therefore no causal relationshipbetween PfS and suicidality can be inferred from this study.
Third, we used single-item measures to make the questionnaireas short as possible. This effort enabled the high response rate,
but we should consider the use of single-item measures as alimitation. Fourth, since no data on suicide attempts wereobtained in our study, we could not examine the association
between PfS and suicide attempt.

Table 2
Associations between preference for solitude, suicidal ideation, and self-harm
Model

1
2
3

Adjusted for

PfS
PfS þ demographic factorsa
PfS þ demographic factorsa þ social isolation

SI

SH

OR

95% CI

p valueOR

95% CI

p value

3.7
3.6
3.1

3.4e4.1
3.3e4.0
2.8e3.4

<.001
<.001
<.001

2.2
2.2
1.9

1.9e2.6
1.9e2.5
1.6e2.3

<.001
<.001
<.001

95% CI ¼ 95% conﬁdence interval; OR ¼ odds ratio; PfS ¼ preference for solitude; SH ¼ self-harm; SI ¼ suicidal ideation.
a
Demographic factors included age, sex, and living with parent(s).

K. Endo et al. / Journal of Adolescent Health xxx (2017) 1e55

Table 3
Associations between four groups and suicidal problems
PfS

Social isolation

SI

SH
Adjusted modela

Unadjusted model
OR
Group 1
Group 2
Group 3
Group 4



þ
þ


þ

þ

Adjusted modela

Unadjusted model

95% CI

p valueOR

95% CI

p valueOR

95% CI

p valueOR

95% CI

p value

Reference
2.3
2.0e2.8
3.2
2.8e3.6
7.7
6.8e8.8

<.001
<.001
<.001

Reference
2.8
2.4e3.3
3.1
2.8e3.5
8.6
7.5e9.9

<.001
<.001
<.001

Reference
1.1.8e1.52.0
1.6e2.4
3.1
2.5e3.8

.640
<.001
<.001

Reference
1.7
1.2e2.3
1.9
1.5e2.2
3.8
3.0e4.8

.002
<.001
<.001

95% CI ¼ 95% conﬁdence interval; OR ¼ odds ratio; PfS ¼ preference for solitude; SH ¼ self-harm; SI ¼ suicidal ideation.
aAdjusted for demographic characteristics (age, sex, and living with parent(s)).

However, an important clinical implication can be induced.
Professionals who work with adolescents should note that adolescents with PfS are more likely to be suicidal than those
without PfS. Also, professionals should note that adolescents
who preferred solitude and were socially isolated were at thehighest risk of SI and SH. Recent research showed that perceived
support from parents and schools may be important for suicide
prevention among adolescents [19]. Parents and relevant professionals should pay attention to socially isolated adolescentsand consider support for them even if they say that they prefersolitude. It may be also worth considering a school education
program which promotes attention and care for students who
prefer for solitude.
Acknowledgments
The authors are grateful to all the adolescents who took partin this study as well as the Board of Education of Tsu City andKochi Prefecture for their cooperation and assistance in conducting this research.
Funding Sources
This work was supported by the Ministry of Health, Labourand Welfare of Japan Scientiﬁc Research Grant (#19-kokoroippan-012), the Ministry of Education, Culture, Sports, Scienceand Technology of Japan Scientiﬁc Research Grant on Innovative
Area (23118004; Adolescent Mind & Self-Regulation) and theTokyo Metropolitan Institute of Medical Science Project Grant(kokoronokenko H27-H32). This study was also supported inpart by JSPS KAKENHI Grant Number JP16H06395, 16H06398,
16H06399 and 16K21720.
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