An Immature Defense Style Is Related to Poor Sleep Quality in Medical Students

Jae-Won Choi; So-Jin Lee; Bong-Jo Kim; Boseok Cha; Dongyun Lee; Eun-Ji Lim; Nuree Kang

doi:10.33069/cim.2025.0067

Chronobiol Med > Volume 7(4); 2025 > Article

Choi, Lee, Kim, Cha, Lee, Lim, and Kang: An Immature Defense Style Is Related to Poor Sleep Quality in Medical Students

Original Article

Chronobiology in Medicine 2025;7(4):247-252.

Published online: December 31, 2025

DOI: https://doi.org/10.33069/cim.2025.0067

An Immature Defense Style Is Related to Poor Sleep Quality in Medical Students

Jae-Won Choi^1,²

, So-Jin Lee^1,²

, Bong-Jo Kim^1,²

, Boseok Cha^1,²

, Dongyun Lee^2,³

, Eun-Ji Lim^2,³

, Nuree Kang^1,²

¹Department of Psychiatry, Gyeongsang National University Hospital, Jinju, Korea

²Department of Psychiatry, Gyeongsang National University School of Medicine, Jinju, Korea

³Department of Psychiatry, Gyeongsang National University Changwon Hospital, Changwon, Korea

Corresponding author: So-Jin Lee, MD, PhD, Department of Psychiatry, Gyeongsang National University School of Medicine, Gyeongsang National University Hospital, 79 Gangnam-ro, Jinju 52727, Korea.
Tel: 82-55-750-8086, E-mail: lifeofzoe@gnu.ac.kr

Received November 7, 2025 Revised November 15, 2025 Accepted November 18, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective

Poor sleep quality is highly prevalent among medical students. Certain personality features, such as defense styles and mechanisms, may be related to poor sleep quality among medical students.

Methods

In total, 146 medical students (45 female, 30.8%) participated in this study. The students completed the Korean version of the Defense Style Questionnaire in their first year and Insomnia Severity Index (ISI), Beck Depression Inventory-II, Beck Anxiety Inventory, and the Composite Scale of Morningness in their third year.

Results

Multiple linear regression analysis revealed that immature defense style (β=0.210, t=2.931, p=0.004) was related to poor sleep quality (i.e., higher ISI score) among the students after controlling for age, sex, depression, anxiety, and chronotype. Regarding defense mechanisms, multiple linear regression analysis revealed that lower sublimation (β=-0.153, t=-2.211, p=0.029), greater humor (β=0.180, t=2.561, p=0.012), and higher withdrawal (β=0.173, t=2.511, p=0.013) were related to poorer sleep quality after controlling for age, sex, depression, anxiety, and chronotype.

Conclusion

An immature defense style could be a risk factor for developing insomnia in medical students. Sublimation may protect against insomnia, whereas humor and withdrawal could be risk factors for insomnia.

Keywords: Sleep quality; Medical students; Immature defense style; Sublimation; Withdrawal

INTRODUCTION

Medical students frequently experience sleep disturbance [1-6]. One meta-analysis reported that the pooled prevalence of poor sleep quality was 52.7% among medical students worldwide [5]. Poor sleep quality may be associated with anxiety, depression, and stress in medical students [2,7,8]. Poor sleep quality can predispose medical students to the onset or aggravation of mental illness [8]. Falloon et al. [9] reported that sleep quality at night before the Objective Structured Clinical Examination (OSCE) in third-year medical students was significantly associated with OSCE scores. In a study involving a large sample of physicians, sleep-related impairments were associated with clinically significant medical errors [10]. If the poor sleep quality of medical students progresses to chronic insomnia when they become physicians, this may be linked to mental health problems and possible medical errors. Therefore, preventing the development of clinical insomnia in medical students is crucial.

Susceptibility to develop insomnia may be related to certain personality features [11]. Neuroticism, internalization, and perfectionism have been associated with insomnia [11,12]. Regarding defense styles and mechanisms, one Korean study revealed that adults with primary insomnia used more undoing and withdrawal than controls [13]. Another study on Korean adolescents reported that poor sleep quality was associated with a high self-inhibiting defense style [14]. Most previous studies concerning personality factors related to insomnia were cross-sectional, and prospective studies are scarce [15]. Therefore, there is a need to evaluate the relationship between defense styles and mechanisms and poor sleep quality among medical students using a prospective design.

In this study, we hypothesized that sleep quality in third-year medical students can be predicted by their defense styles during the first year of medical school. Similarly, we hypothesized that certain defense mechanisms are also related to the sleep quality of medical students.

METHODS

At the beginning of February 2021 and February 2022, we recruited first-year medical students from Gyeongsang National University (GNU) in Jinju City, Republic of Korea. Before participation, we provided a detailed explanation of the study aims and protocols to the students. All students who agreed to participate (n=146) provided written informed consent and completed the Korean version of the Defense Style Questionnaire (K-DSQ) during the first week of their first year of medical school. Upon reaching their third year of medical school in 2023 and 2024, the students completed the Korean versions of the Insomnia Severity Index (K-ISI), Beck Depression Inventory-II (K-BDI-II), Beck Anxiety Inventory (K-BAI), and Composite Scale of Morningness (CSM). This study was approved by the Institutional Review Board of Gyeongsang National University Hospital (2025-05-021-001).

Assessments

The self-reported questionnaires distributed to first-year students included the K-DSQ, and the self-reported questionnaires administered to third-year medical students comprised the K-ISI, K-BDI-II, K-BAI, and CSM. The K-DSQ was used to assess defense styles and mechanisms using a 7-point Likert scale (range: 1–7). The K-DSQ is a psychometrically pertinent instrument consisting of 65 questions that examine individual thoughts and behavior [16]. Sixteen defense mechanisms are explored, organized into four defense styles: adaptive (humor, sublimation, omnipotence, and denial), self-repressive (suppression, reaction formation, undoing, and withdrawal), conflict-avoiding (resignation, isolation), and immature (consumption, passive aggression, fantasy, splitting, projection, and acting out) [16]. The classification of defense style is based on a validation study conducted with 465 Korean college students (144 male, 321 female), which might reflect some cultural and psychological features of Korean Millennials in that phase of time [16].

The K-ISI is a reliable and valid instrument for evaluating insomnia severity [17,18]. ISI is a brief screening tool for insomnia [17] that measures the severity of insomnia, degree of satisfaction with sleep patterns, degree to which insomnia interferes with daily functions, how apparent the person’s insomnia is to others, and overall distress caused by the sleep problem [17]. The K-ISI consists of seven items, each rated on a 5-point Likert scale (range: 0–4) [18]. Higher scores indicate more severe insomnia, and the optimal cutoff for Koreans is 15.5 [18]. The internal consistency of the K-ISI was appropriate (Cronbach’s α=0.865).

The BDI-II, developed by Beck et al. [19], is a tool to assess individual depression. The K-BDI-II comprises 21 items rated on a 4-point Likert scale (range: 0–3) [20]. The K-BDI-II is a reliable and valid instrument for assessing depression [20,21]. Higher scores indicate depression, and the cutoff value is reportedly >18 [20]. The internal consistency in this study was appropriate (Cronbach’s α=0.905).

The BAI was developed by Beck et al. [22] to assess a person’s anxiety. This self-reported questionnaire comprises 21 items rated on a 4-point Likert scale (range: 0–3) [22,23]. The K-BAI is a reliable and valid tool for evaluating anxiety in Korean [23,24]; higher scores indicate greater anxiety [22,23]. The internal consistency of the K-BAI in this study was good (Cronbach’s α=0.88).

The CSM is a self-reported instrument developed to assess an individual’s chronotype [25]. This instrument comprises 13 items: 3 using 5-point Likert scales (range: 1–5) and 10 using 4-point Likert scales (range: 1–4) [25,26]. The total scores range 13–55, with higher scores indicating morningness and lower scores indicating eveningness [25,26]. This instrument has been reported to be reliable in the Korean population [27]. The CSM score was used as a continuous variable in this study, and its internal consistency was appropriate (Cronbach’s α=0.795).

Statistical analysis

Differences in the ISI scores between men and women were evaluated using an independent t-test. Multiple linear regression analyses were conducted to determine the relationships between defense styles or mechanisms and sleep quality. To determine the relationship between defense style and insomnia severity, we used the ISI score in the third year of medical school as the dependent variable and used defense style in the first year as a predictor while controlling for age, sex, depression, anxiety, and chronotype in the third year. The three variables, which include depression, anxiety, and chronotype, are known to be associated with insomnia severity. To investigate the relationship between defense mechanisms and insomnia severity, we used ISI in the third year as a dependent variable and defense mechanisms in the first year as a predictor while controlling for age, sex, depression, anxiety, and chronotype in the third year. All analyses were performed using SPSS for Mac (version 27.0; IBM Corp.). Statistical significance was defined as a two-tailed p-value <0.05.

RESULTS

In total, 146 medical students (45 female; 30.8%) participated in this study. The mean age of the students was 25.28±2.41 years (range, 22–37) in the third year. Of the participants, 65 (44.5%) were in their third year of medical school in 2023, and 81 (55.5%) were in their third year of medical school in 2024. Nine of 141 students (6.38%) had ISI scores that exceeded the cutoff value (15.5). The mean ISI score was 4.98 (standard deviation [SD]=4.54; n=141). The ISI score of male students (5.55±4.69) was higher than that of female students (3.73±3.96) (t(139)=-2.235, p=0.027). Ten (6.85%) students had BDI-II scores greater than the cutoff value (18). The mean BDI-II was 6.03 (SD=6.32; n=146). The mean BAI score was 2.44 (SD=4.15; n=143), and the mean CSM score was 32.22 (SD=5.33; n=146).

Multiple linear regression analysis revealed that immature defense style (β=0.210, t=2.931, p=0.004) was related to poorer sleep quality (i.e., higher ISI score) after controlling for age, sex, depression, anxiety, and chronotype (Table 1). This model also showed that younger age (β=-0.146, t=-2.126, p=0.036), male sex (β=0.182, t=2.596, p=0.011), depression (β=0.389, t=4.182, p<0.001), and anxiety (β=0.201, t=2.254, p=0.026) predicted poor sleep quality (Table 1).

Regarding defense mechanisms, multiple linear regression analysis revealed that lower sublimation (β=-0.153, t=-2.211, p=0.029), greater humor (β=0.180, t=2.561, p=0.012), and higher withdrawal (β=0.173, t=2.511, p=0.013) were related to poorer sleep quality after controlling for age, sex, depression, anxiety, and chronotype (Table 2). Additionally, younger age (β=-0.151, t=-2.213, p=0.029), male sex (β=0.173, t=2.504, p=0.014), depression (β=0.446, t=4.859, p<0.001), anxiety (β=0.192, t=2.180, p=0.031), and eveningness (β=-0.141, t=-1.989, p=0.049) predicted poor sleep quality (Table 2).

DISCUSSION

Our findings revealed that immature defense style in the first year of medical school was related to the students’ sleep quality in the third year. The more immature the defense style, the poorer the sleep quality. Regarding defense mechanisms, lower sublimation, greater humor, and higher withdrawal in the first year predicted poor sleep quality in the third year of medical school.

This study suggests that a greater immature defense style at the beginning of medical school may result in insomnia among medical students. Individuals with a highly immature defense style may manage their impulses and desires immaturely [16]. Similarly, among patients with early non-metastatic colorectal cancer, an immature defense style predicted sleep disturbance after 1-year follow-up [28]. The immature defense style is closely related to neuroticism [29]. Previous studies on the association between insomnia and personality traits have shown that neuroticism is the strongest and most consistent risk factor for insomnia [11,12,15,30]. Blagrove and Akehurst [31] also reported that mood depression due to sleep deprivation was significantly associated with neuroticism. In this study, among the personality factors investigated, only a high level of neuroticism had an impact on increasing the mood-depressing effect of experimentally induced insomnia. Individuals with high neuroticism tend to engage in emotion-focused strategies that can lead to sleep disruptions [32]. Neuroticism, as well as immature defense style, may be important risk factors for insomnia. Therefore, assessing immature defense styles among medical students may allow for the early detection of preclinical insomnia [12].

In this study, we found that lower sublimation, greater humor, and higher withdrawal rates in the first year of medical school were related to poorer sleep quality in the third year. A previous study found that patients with insomnia and no history of depression used more undoing and withdrawal than normal controls [13]. Among Korean high school students, a self-inhibiting defense style was associated with poor sleep quality [14]. In the K-DSQ, withdrawal and undoing are elements of a self-inhibiting defense style [16]. Withdrawal is a defense mechanism that protects oneself by distancing oneself from others in stressful situations [16]. This study suggests that high withdrawal in medical students may lead to insomnia within a few years of medical education. Sublimation and humor belong to the adaptive defense styles of the K-DSQ [16]. The relation of sublimation and humor with insomnia risk has not yet been reported. Therefore, the finding that less sublimation and high humor might lead to insomnia among medical students requires further research with larger sample sizes. Sublimation and humor are defense mechanisms that represent mature defense and are associated with the tendency to deal with inner impulses and desires in an adaptive and constructive manner [16]. According to our findings, sublimation may protect individuals from developing insomnia; however, humor may also increase the risk of insomnia.

Our findings suggest that male sex was associated with poor sleep quality among medical students. This finding is inconsistent with those of other studies involving medical students. Female medical students reportedly had higher Pittsburgh Sleep Quality Index (PSQI) scores (i.e., poorer sleep quality) than male students. However, this sex difference was not found among non-medical students [33]. Another study on Pakistani medical students reported that female students exhibited poorer sleep (higher PSQI scores) than male students [34]. A meta-analysis of epidemiological studies on insomnia prevalence showed that females have a higher risk of insomnia in all age groups (>15 years) [35]. However, one investigation using actigraphy in 32 individuals (mean age 44.76) revealed that women had better sleep quality than men [36]. Another polysomnographic finding showed no sex differences between the primary insomnia group and healthy controls [37]. Sex differences in the degree of insomnia among medical students cannot be concluded without future studies with objective measures of sleep in larger numbers of participants.

The multiple linear regression analysis examining the relationship between sleep quality and defense mechanisms also revealed that eveningness in the third year was associated with poor sleep quality among our medical students. A previous study reported that eveningness of university students was associated with poor sleep quality [38]. However, another study conducted with Islamic medical students showed that morningness was associated with poorer sleep quality [39]. Eveningness could be linked to higher social jetlag, which was reported to be associated with poor sleep quality among Korean adolescents [14]. Further research is needed to investigate how eveningness contributes to poor sleep quality among medical students.

Identifying medical students who are at a higher risk of insomnia is very important. According to our findings, students who use a more immature defense style may be prone to insomnia after 2 years of medical education. Individuals who are highly neurotic are known to experience guilt easily [40]. In 1947, Rothenberg [41] presented a psychoanalytic insight into insomnia and argued that neurotic patients with repressed guilty feelings for a prolonged time could easily develop insomnia, especially after encountering a real death situation. Notably, medical students frequently experience patient death and substantial emotional distress when coping with patients’ deaths during clerkships [42]. In our study, the ISI score was measured at the beginning of clerkship. When students with highly immature defense styles in their first year encounter patient deaths during clerkship, they might easily progress to clinical insomnia. We suggest that screening students with highly immature defenses at the start of medical education can help prevent the onset of insomnia during the medical school years, especially during clerkships. A previous study reported that patients with neurotic insomnia benefited more from cognitive behavioral treatment than those with non-neurotic insomnia [43]. Therefore, for students with highly immature defenses, a cognitive-behavioral approach before insomnia onset would help prevent the development of insomnia disorders.

This study has some limitations. First, the degree of insomnia was measured using a self-reported questionnaire, the ISI. Objective tests, such as actigraphic data collected over several weeks and repeated polysomnography, would have been better validated tool choices. Second, although this study used a prospective design, factors that may influence individuals’ defense styles and mechanisms, such as anxiety and depression at baseline, were not controlled for. Third, our sample size was relatively small. Fourth, as this study was conducted at a single medical school, the generalizability of the results should be interpreted with caution.

Despite these limitations, this study has several strengths. First, owing to the prospective study design, the relationship between defense style or mechanisms and degree of insomnia was fairly elucidated. Second, variables such as anxiety, depression, and chronotype, which may be associated with insomnia, were controlled for in the multiple regression analysis of insomnia.

In conclusion, an immature defense style could be a risk factor for developing insomnia in medical students. Sublimation may protect against insomnia, whereas humor and withdrawal could be risk factors for insomnia. These findings could be used to prevent the development of insomnia and screen individuals at risk for insomnia during their medical school years.

NOTES

Conflicts of Interest

The authors have no potential conflicts of interest to disclose.

Availability of Data and Material

The datasets generated or analyzed during the study are available from the corresponding author on reasonable request.

Author Contributions

Conceptualization: Jae-Won Choi, So-Jin Lee, Boseok Cha. Data curation: So-Jin Lee, Jea-Won Choi. Funding acquisition: Bong-Jo Kim, So-Jin Lee, Boseok Cha. Investigation: all authors. Methodology: So-Jin Lee, Dongyun Lee, Jae-Won Choi. Project administration: all authors. Resources: Bong-Jo Kim, So-Jin Lee, Boseok Cha, Jae-Won Choi. Software: Bong-Jo Kim, So-Jin Lee, Boseok Cha, Jae-Won Choi. Supervision: Bong-Jo Kim, Boseok Cha. Validation: all authors. Visualization: Jae-Won Choi, Nuree Kang. Writing—original draft: So-Jin Lee, Boseok Cha, Jae-Won Choi. Writing—review & editing: all authors.

Funding Statement

None

Acknowledgments

None

Table 1.

Multiple linear regression model predicting sleep quality in third year medical students according to their defense style in the first year of medical school

Variables	B	Standard error	β	t	p-value
Age	-0.414	0.195	-0.146	-2.126	0.036
Male (vs. female)	1.795	0.692	0.182	2.596	0.011
BDI-II (in the third year of medical school)	0.283	0.068	0.389	4.182	<0.001
BAI (in the third year of medical school)	0.220	0.098	0.201	2.254	0.026
CSM (in the third year of medical school)	-0.082	0.061	-0.096	-1.333	0.185
Immature defense style (in the first year of medical school)	1.457	0.497	0.210	2.931	0.004

Model statistics: Adjusted R2=0.467, F=18.548 (p<0.001). BDI-II, Beck Depression Inventory-II; BAI, Beck Anxiety Inventory; CSM, Composite Scale of Morningness

Table 2.

Multiple linear regression model predicting sleep quality in third year medical students according to their defense mechanisms in their first year of medical school

Variables	B	Standard error	β	t	p-value
Age	-0.440	0.199	-0.151	-2.213	0.029
Male (vs. female)	1.734	0.693	0.173	2.504	0.014
BDI-II (in the third year of medical school)	0.337	0.069	0.446	4.859	<0.001
BAI (in the third year of medical school)	0.214	0.098	0.192	2.180	0.031
CSM (in the third year of medical school)	-0.122	0.061	-0.141	-1.989	0.049
Sublimation (in the first year of medical school)	-0.587	0.265	-0.153	-2.211	0.029
Humor (in the first year of medical school)	0.701	0.274	0.180	2.561	0.012
Withdrawal (in the first year of medical school)	0.520	0.207	0.173	2.511	0.013

Model statistics: Adjusted R²=0.481, F=15.045 (p<0.001). BDI-II, Beck Depression Inventory-II; BAI, Beck Anxiety Inventory; CSM, Composite Scale of Morningness.

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