Shinshu Med J, 71⑴：43～52, 2023

Causes of Excessive Daytime Sleepiness inJapanese Medical Students : A Cross-sectional Study
Haruka Suzuki1）, Keisaku Fujimoto2）＊, Tomoya Hazu3）
Riho Seki3） and Haruka Wada3）
1） Department of Biomedical Laboratory Sciences, Graduate School of Medicine, Shinshu University2） Department of Clinical Laboratory Sciences, Shinshu University School of Health Sciences
3） Students of Inspection Technology Sciences, Shinshu University School of Health Sciences

Background : Most surveys regarding excessive daytime sleepiness (EDS) in university students have used only
questionnaires. The present study was performed to clarify the causes of EDS and the characteristics of students
with EDS using a sleep diary, polysomnography (PSG), and multiple sleep latency testing (MSLT) in addition toquestionnaires.
Methods : Medical students with and without EDS were recruited using a poster. EDS was defined as Japanese
Epworth Sleepiness Scale score ≥ 11, and all participants underwent PSG and MSLT. They were also asked torecord a sleep diary for 1 month and to complete the Japanese version of the Pittsburgh Sleep Quality Index,
the Sleep Hygiene Index, and lifestyle questionnaires. Sleep disorders were diagnosed based on the International
Classification of Sleep Disorders, and the characteristics were compared between students with and without EDS.
Results : Among the 59 students who participated in the study, 33 were classified as having EDS and the re­maining 26 did not have EDS. In the EDS group, 16 students were diagnosed with insufficient sleep syndrome(ISS), six had narcolepsy, five had insomnia, three had idiopathic hypersomnia, one had delayed sleep-wakephase disorder, one had obstructive sleep apnea, and one had periodic limb movement disorder. The question­
naires revealed that the most important factor for EDS was poor sleep hygiene due to their lifestyle.
Conclusion : The survey including PSG and MSLT revealed that approximately half of the medical students with
EDS showed ISS followed by narcolepsy, insomnia, and other sleep disorders, and the main characteristic of thestudents with EDS was poor sleep hygiene. Shinshu Med J 71 : 43―52, 2023
(Received for publication February 14, 2022 ; accepted in revised form September 12, 2022)
Key words : polysomnography, multiple sleep latency test, Epworth sleepiness scale, sleep hygiene
which may be related to insufficient sleep syndrome

Ⅰ Introduction(ISS), and 36 ％ of medical students in Morocco com­

Medical students have been reported to show poor

plained of EDS1）. In a questionnaire survey, 43 ％ ofquality of sleep and low academic performance due

Japanese university students reported dozing off more1）

to excessive daytime sleepiness (EDS) . Questionnairethan once per day during lectures, and 42.3 ％ andsurveys have also shown that 51 ％ of medical stu­37.8 ％ slept for only 6-7 hours or ＜ 6 hours, respec­2）

3）

and 25 ％ of those in the USA

tively4）. In addition, a questionnaire survey using

had a short sleeping time of less than 7 h per night,

SLEEP-50 demonstrated that 12.0 ％ of university

dents in Malaysia

students in the southeastern USA had insomnia,＊

Corresponding author : Keisaku Fujimoto
Respiratory Medicine, Hospital Director,
Omachi Municipal General Hospital, 3130 Omachi,
Omachi-city, Nagano 398-0002, Japan
E-mail : fkeisaku@shinshu-u.ac.jp

No. 1, 2023

16.0 ％ had narcolepsy, 8.0 ％ had restless legs syn­drome (RLS) or periodic limb movement disorder(PLMD), 7.0 ％ had circadian rhythm disorder, and
4.0 ％ had other hypersomnia and obstructive sleep
43Suzuki・Fujimoto・Hazu et al.

apnea (OSA)5）. However, most previous studies re­and MSLT in addition to questionnaires.

garding EDS in university students were based onlyⅡ

on questionnaire surveys and did not include objec­
tive examination of the causes of EDS using bothＡ

Materials and Methods

Subjects

polysomnography (PSG) and multiple sleep latency

This cross-sectional study was conducted in atest (MSLT). Both PSG and MSLT in addition to a

population of medical students at Shinshu University

sleep diary are necessary to make accurate diagno­

School of Medicine and Health Sciences from Julyses of sleep disorders causing EDS, such as OSA, ISS,2017 to December 2020. Posters about the study

narcolepsy, idiopathic hypersomnia (IH), delayed

were displayed on the campus to call for the partici­

sleep-wake phase disorder (DSWPD), PLMD, etc.

pation of two groups of medical students with and

OSA is characterized by frequent periodic sleep

without EDS. All subjects were given an adequate

apnea due to upper airway obstruction during sleep,

explanation of the study and provided written in­which causes periodic hypoxemia, sleep fragmenta­

formed consent to participation. Students who hadtion, and lack of deep sleep, resulting in EDS. Afteralready been diagnosed with any sleep disorders andexclusion of other apparent sleep disorders, a diagno­

were undergoing treatment with medications, such

sis of ISS is based on a shorter time in bed thanas hypnotic agents, antihistamines, psychotropic

expected for age on most days for at least 3 months

agents, and antianxiety medications, were excluded.

leading to inability to have the necessary sleep time,

Ｂ

Protocolresulting in EDS, and the disappearance of EDS

The students were divided using the Japanese ver­when longer sleep times can be obtained. Narcolepsy

sion of the Epworth Sleepiness Scale (JESS)6）into theis diagnosed by the presence of EDS for at least 3

EDS group (JESS score ≥ 11) and non-EDS groupmonths and mean sleep latency ＜ 8 min with evi­

(JESS score ＜ 11). All subjects answered the Pitts­

dence of two or more sleep-onset REM periods

burgh Sleep Quality Index (PSQI)7） and Japanese(SOREMPs) on MSLT with (Type 1) or without clear

version of the Sleep Hygiene Index (J-SHI)8）, record­

cataplexy (Type 2). IH is diagnosed by the presence

ed a sleep diary for 1 month, and then underwentof EDS for at least 3 months and mean sleep latency

PSG and MSLT. They were also asked about their＜ 8 min with evidence of less than two SOREMPs

lifestyle (exercise habits, alcohol drinking, smoking,on MSLT and absence of cataplexy and hypocretin

frequency of skipping breakfast, frequency of part-

deficiency (if measured), and no other identifiable

time jobs, and club activities) using a questionnaire.

causes, such as narcolepsy, OSA, etc. DSWPD is

Finally, sleep disorders were diagnosed based on thecharacterized by habitually delayed sleep-wakeInternational Classification of Sleep Disorders - Third

timing, usually greater than 2 h, relative to conven­

Edition (ICSD-3)9） by the corresponding author

tional or socially acceptable timing and difficulty

who is a member of the Japanese Society of Sleep

falling asleep at a time required to obtain sufficient

Research. This study was conducted in accordance

sleep duration on a school or work night and arisingwith the International Conference on Harmoniza­

at the required times. PLMD is characterized by fre­tion-Good Clinical Practice and the Declaration ofquent involuntary limb movement during sleep ac­

Helsinki (2008) and was approved by the institutional

companied by sleep disturbance or other functional

research ethics committee of Shinshu University

impairment. Students with diagnoses such as narco­

School of Medicine (No. 3736, July 5, 2017).

lepsy, SAS, PLMD, and idiopathic hypersomniaＣrequire specific therapies for these sleep disorders.

１ Japanese version of the Epworth Sleepiness Scale

The present study was performed to clarify the

Evaluation methods(JESS)

causes of EDS and the characteristics of Japanese

JESS is a self-rated questionnaire to measure themedical students with EDS using a sleep diary, PSG,

degree of sleepiness based on a score of 0-3 points

44

Shinshu Med J

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EDS in medical students

for each of eight situations. A total score ≥ 11 is taken
6）muscle and right and left tibialis anterior muscles.

to indicate EDS .

Other channels were nasal pressure, oronasal airflow,

２ Pittsburgh Sleep Quality Index (PSQI) and life­

thoracoabdominal inductance plethysmogram, percu­

style questionnairetaneous oxygen saturation (SpO2), neck microphone,

PSQI is a self-rated questionnaire that assesses

body position sensors, and a modified lead II ECG.

sleep quality and disturbances over a 1-month period.

PSG data were analyzed using POLYSMITH ver. 7.0

Nineteen individual items generate seven component(Nihon Kohden, Tokyo, Japan), and the analyses werescores : subjective sleep quality, sleep latency, sleep

carried out both automatically and manually in ac­

duration, habitual sleep efficiency, sleep disturbance,

cordance with the recommendations of the AASM12）.

use of sleeping medication, and daytime dysfunction.

５

A total score for these seven components ≥ 6 points
7）.

is taken to indicate poor quality of sleep

Multiple sleep latency test
MSLT was conducted according to the guidelinesof the Japanese Society of Sleep Research13） on the

The lifestyle questionnaire is a self-rated question­

day after PSG examination. Monitoring was repeatednaire to assess lifestyle habits. The questionnaire

five times at 08 : 00, 10 : 00, 12 : 00, 14 : 00, and 16 : 00.

elicited responses regarding the number of times per

In this test, we measured sleep latency and REM

week the participant exercised, drank alcohol, skip­

sleep latency in each nap. The test was finished if noped breakfast, and engaged in activities at night andsleep occurred within 20 minutes after turning off thewhether they were a current smoker or not.

lights or was continued for 15 minutes after onset of

３ Japanese version of Sleep Hygiene Index (J-SHI)

sleep.

The Sleep Hygiene Index (SHI) is a self-reported
10）

Ｄ

Statistical analysis

to assess sleep

Values in the text, tables, and figures are shown as

hygiene behaviors. SHI translated into Japanesethe means ± standard deviation (SD). Fisher’s exact

index developed by Mastin et al.

8）(Japanese version of SHI : SHPS-J) was used in thistest was used for statistical analysis of the ratio ofstudy. The 13 questions were scored on a scale rang­

smokers and the subjects who showed shorter sleep

ing from 0 to 4 defined as follows : 0, never ; 1, rarely

latency defined as mean sleep latency in 5 naps ＜ 8; 2, sometimes ; 3, frequent ; and 4, always. In thismin on MSLT. Welch’s t test was used for otherstudy, the responses “frequently (3 points)” and “always

analyses. In all analyses, P ＜ 0.05 was taken to indi­(4 points)” in each item were defined as indicating poor

cate statistical significance.

sleep hygiene.
４

Ⅲ

PolysomnographyStandard overnight attended PSG was performed

Ａ

Results

Causes of EDS in medical students

starting at 20 : 00, and the data were collected from

Among the total of about 1320 medical students on

21 : 00 to 06 : 00 the next morning. PSG was recorded

the campus, 59 students (23 men) with a mean age ofwith a digital polygraph (EEG-9200 ; Teijin Pharma

21.6 ± 1.6 years participated in this study. These

Co. Ltd., Tokyo, Japan) according to the guidelines ofstudents were divided into the EDS group (n＝33)

the American Academy of Sleep Medicine (AASM)

and non-EDS group (n＝26) based on their JESSManual for Scoring of Sleep and Associated Events

scores. In the EDS group, ISS was the most common

11）version 2.1 . First, one ground channel, F3-M2, F4-

cause of EDS (n＝16) (Table 1). Six students were

M1, C3-M2, C4-M1, O1-M2, and O2-M1 channels werediagnosed with narcolepsy (type 1 (NT1), n＝3 ; typechosen for EEG, and monitoring was applied in ac­

2 (NT2), n＝3) ; five had insomnia (IN), all of whom

cordance with the instructions of the 10-20 Interna­

showed hypnagogic disorder ; and one also woke intional Placement System. Electrooculography was

the middle of the night. Three students were diag­

recorded from right and left corners of the eyes, andnosed with idiopathic hypersomnia (IH), one withelectromyography was recorded from the submental

delayed sleep-wake phase disorder (DSWPD), one

No. 1, 2023

45

Suzuki・Fujimoto・Hazu et al.
Table 1 Causes of excessive daytime sleepiness (EDS) in medical students, that werediagnosed in accordance with the International Classification of Sleep Disorders Third Edition (ICSD-3)

NumberNormalISS
IN
Narcolepsy Type 1
Narcolepsy Type 2
IH
OSA
DSWPD
PLMD

EDS

non-EDStotal

33
0 (0.0)16 (48.5)
5 (15.2)
3 (9.1)3 (9.1)3 (9.1)1 (3.0)1 (3.0)1 (3.0)2625 (96.2)
000001 (3.8)
0
0

59
25
16
5
3
3
3
2
1
1

Values are number and ( ) is ％. EDS was identified based on Japanese Epworth Sleepiness
Scale (JESS) score ≥ 11.
Abbreviations : DSWPD, delayed sleep-wake phase disorder ; IH, idiopathic hypersomnia ; IN,
insomnia ; ISS, insufficient sleep syndrome ; OSA, obstructive sleep apnea ; PLMD, periodic
limb movement disorder.

Table 2

Number, n (％)
PSG
SL, min
REM latency, min
Sleep efficiency, ％Sleep architecture
Stage W, ％Stage N1, ％Stage N2, ％Stage N3, ％Stage REM, ％AI, events/h
AHI, events/h
PLMI, events/h
MSLT
SL, min
Number of REM, n

Results of PSG and MSLT in the EDS group

ISS

NA

IN

IH

DSWPD

OSA

PLMD

16 (48.5)

6 (18.2)

5 (15.2)

3 (9.1)1 (3.0)1 (3.0)1 (3.0)12.9 ± 11.9
93.5 ± 34.5
95.5 ± 3.6

8.5 ± 4.5
61.2 ± 25.0
95.2 ± 2.6

23.7 ± 23.7
149.9 ± 56.2
86.9 ± 12.8

9.3 ± 7.6
109.3 ± 36.5
93.7 ± 1.6

4.0
90.4
93.5

20.5
91.5
93.5

4.0
97.0
95.0

4.5 ± 3.6
8.8 ± 4.4
46.8 ± 6.9
22.4 ± 6.4
17.4 ± 4.4
10.6 ± 4.3
2.5 ± 1.9
2.1 ± 3.2

4.8 ± 2.6
8.4 ± 2.2
47.2 ± 6.8
20.7 ± 5.7
18.9 ± 4.4
10.5 ± 3.6
2.1 ± 1.7
4.6 ± 6.2

13.1 ± 12.7
10.6 ± 4.3
39.9 ± 7.1
21.1 ± 5.9
15.3 ± 4.4
12.7 ± 5.7
3.7 ± 2.7
2.7 ± 3.4

6.3 ± 1.6
12.9 ± 5.7
52.2 ± 6.5
12.9 ± 3.1
15.7 ± 3.2
11.4 ± 1.1
1.8 ± 1.1
3.0 ± 1.9

6.5
8.0
49.1
17.1
19.4
15.4
1.4
5.6

6.5
9.3
52.3
11.7
20.2
9.9
7.8
12.8

5.0
6.5
51.9
17.1
19.6
14.9
0.1
26.3

5.8 ± 3.7
1.1 ± 1.3

3.5 ± 0.6
3.5 ± 1.1

8.0 ± 3.6
0.6 ± 0.8

2.5 ± 0.9
0.7 ± 0.5

4.3
2.0

9.6
0.0

1.3
0.0

Values are mean ± standard deviation (SD). EDS was identified by the scores of the Japanese Epworth Sleepiness
Scale (JESS) ≥ 11.
Abbreviations : AHI, apnea hypopnea index ; AI, arousal index ; DSWPD, delayed sleep-wake phase disorder ; EDS,
excessive daytime sleepiness ; IH, idiopathic hypersomnia ; IN, insomnia ; ISS, insufficient sleep syndrome ; MSLT,
multiple sleep latency test ; NA, narcolepsy ; OSA, obstructive sleep apnea ; PLMD, periodic limb movement
disorder ; PLMI, periodic limb movement index ; PSG, polysomnography ; SL, sleep latency.

with OSA, and one with PLMD. In the non-EDS

shows the results of PSG and MSLT in each sleep

group, only one student was diagnosed with OSA

disorder in the EDS group. The students with ISS(apnea hypopnea index [AHI]＝15.4 events/h). Table 2

showed no abnormalities on PSG. Furthermore, some46

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EDS in medical students
Table 3Comparison of the results of PSG and MSLT between the EDS and non-EDS groups

NumberPSG
SL, min
REM latency, min
Sleep efficiency, ％Sleep architecture
Stage W, ％Stage N1, ％Stage N2, ％Stage N3, ％Stage REM, ％AI, events/h
MSLT
Mean SL, min
SL ＜ 8 min in 5 naps, n
Number of REM, nEDS

non-EDS

P-value33

26

13.1 ± 13.7
97.5 ± 43.8
93.8 ± 6.4

13.1 ± 9.9117.1 ± 39.3
89.3 ± 6.8

0.761
0.097
0.020

6.2 ± 6.4
9.3 ± 4.2
46.7 ± 7.0
20.4 ± 6.4
17.4 ± 4.2
11.2 ± 4.2

10.7 ± 6.8
12.5 ± 5.4
51.4 ± 11.1
15.2 ± 7.8
12.0 ± 3.2
12.0 ± 4.9

0.019
0.022
0.059
0.008
＜ 0.001
0.559

5.7 ± 3.722
1.3 ± 1.4

8.2 ± 3.44
0.5 ± 0.8

0.010
＜ 0.001
0.016

Values are means ± SD. EDS was identified based on Japanese Epworth Sleepiness Scale (JESS)
score ≥ 11.
Abbreviations : AI, arousal index ; EDS, excessive daytime sleepiness ; MSLT, multiple sleep
latency test ; PSG, polysomnography ; REM, rapid-eye movement ; SL, sleep latency.

students showed SOREMPs once or twice during

Table 4 shows the mean ± SD daily bedtime,

MSLT. All students with narcolepsy showed normal

wake-up time, and total sleep time for 1 month in

PSG, and short sleep latency (＜ 8 min), and at least

each individual subject. The mean bedtime was sig-

two had SOREMP with a mean of 3.5 SOREMP

nificantly later in the EDS group than that in theduring MSLT. The sleep latency was ＞ 20.0 minutes

non-EDS group. However, there were no significant

in two of five students with insomnia (mean sleep

differences in wake-up time or total sleep time be-latency : 23.7 ± 23.7 min on PSG). One student withtween the two groups. The SDs of bedtime, wake-up

AHI of 7.8 events/h was diagnosed with OSA bytime, and total sleep time were significantly greater

PSG. In one student with PLMD, periodic limb move-in the EDS group than the non-EDS group. Table 5

ment index (PLMI) was 26.3 events/h and PLMI withshows the PSQI score and lifestyle questionnaire

arousal was 8.2 events/h on PSG, so PLMD was diag-results in the two groups. The PSQI scores were

nosed as the cause of EDS. Table 3 shows a compar-

higher in the EDS group than the non-EDS group,ison of the results of PSG and MSLT between theand 20 students in the EDS group had scores ＞ 6

EDS and non-EDS groups. The percentages of sleep

points compared to only two students in the non-EDS

efficiency, stage N3, and stage REM on PSG weregroup. There were no significant differences in thesignificantly increased, while the percentages oflifestyle questionnaire results between the twostage wake and stage N1 on PSG were significantly

groups. Table 6 shows the results of J-SHI. The

decreased in the EDS group compared to the non-total scores and scores of item numbers 1, 2, 3, 6, 7,

EDS group. The mean sleep latency in MSLT was

8, 12, and 13 were significantly higher in the EDS

shorter and the frequency of SOREMP was higher

group than the non-EDS group. The items of ques-(both P ＜ 0.01) in the EDS group than the non-EDS

tions 1, 2, and 3 suggested that the students in thegroup.

EDS group had poor sleep habits, while the others

Ｂ Results of circadian rhythm, PSQI, lifestylesuggested poor sleep environments.

questionnaire, and J-SHI
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47

Suzuki・Fujimoto・Hazu et al.
Table 4Comparison of sleep diaries between EDS and non-EDS groups

Number
Bedtime (O’clock)SD for bedtime, minute
Wake-up time (O’clock)SD for wake-up time, minuteTotal sleep time (hours)
SD for total sleep time, minute

EDS

non-EDS

P-value33
0 : 58 ± 1 : 03
91 ± 35
7 : 56 ± 0 : 52
93 ± 38
6.98 ± 0.92
97 ± 3126
0 : 28 ± 0 : 34
40 ± 16
7 : 42 ± 0 : 53
55 ± 19
7.23 ± 0 : 85
51 ± 22

＜0.05
＜0.01
0.827
＜0.01
0.298
＜0.01

Values are means ± standard deviation (SD). EDS was identified based on Japanese Epworth
Sleepiness Scale (JESS) score ≥ 11 ; SD for bedtime, wake-up time, and total sleep time, mean valuesof standard deviation (SD) of bedtime, wake-up time, and total sleep time for 1 month in eachindividual subject.
Table 5 Comparison of PSQI score and Interviewed lifestyle questionnaire between EDS and non-EDS groups

NumberPSQI score
Interviewed Lifestyle questionnaire
Exercise habit/week, times
Drinking alcohol, times/week
Current smoker, nSkipping breakfast, times/week
Activities at night, times/week

EDS

non-EDS

P-value33
6.4 ± 2.026
2.8 ± 1.7

＜ 0.001

1.5 ± 1.3
0.5 ± 0.63
1.1 ± 2.2
2.5 ± 2.0

0.9 ± 1.2
0.6 ± 1.50
1.7 ± 2.9
1.5 ± 1.4

0.730
0.790
0.248
0.409
0.174

Values are means ± SD. Poor quality of sleep was identified based on PSQI score ≥ 6.
Abbreviations : EDS, excessive daytime sleepiness ; PSQI, Pittsburgh Sleep Quality Index.

Ⅳ Discussion

insomnia in 15.2 ％, IH in 9.1 ％, OSA in 3.0 ％, and
PLMD in 3.0 ％. On the other hand, the only sleeping

Medical students have been reported to show poor

disorder found in the non-EDS group was mild tosleep quality, EDS, and reduced academic perfor-

moderate OSA, which was seen in one student. Both

1）
-3）
14）
15）

. However, most surveys performed tonarcolepsy with cataplexy (type 1) and narcolepsy

date were based only on questionnaires, and PSG andwithout cataplexy had prevalence rates of 0.22 ％MSLT have not been used to evaluate sleep quality

among the about 1340 medical students included inand sleep disorders. The goal of this study was notthis study in contrast to the prevalence rates of

to determine the prevalence of EDS among medical

0.16 ％ (type 1) and 1 ％-3 ％ (type 2) in the general

students. As participants with and without EDS wereJapanese population (https://jssr.jp/files/guideline/

recruited using posters, the EDS group was larger

narcolepsy.pdf). Diagnosis of some sleep disorders

due to a higher level of concern about sleep quality inrequires PSG and MSLT, and we were able to clarify

these subjects. However, by using both PSG and

the accurate causes of EDS, including SAS, narcolep-

MSLT in addition to questionnaires, the precise

sy, etc. A cross-sectional survey using the SLEEP-50

causes of EDS in Japanese medical students whoquestionnaire in a population of medical students incomplained of EDS were elucidated. In the present

Jordan demonstrated that 30.7 ％ of the students

study, the most common sleep disorder responsible

were short sleepers and 66.2 ％ had at least one

for EDS was ISS, which was seen in 48.5 ％ of partic-

sleep disorder15）. The most common sleep disorders

ipants (Table 1), followed by narcolepsy in 18.2 ％,were hypersomnia (23.1 ％ ) and insomnia (18.3) fol-

mance

48

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EDS in medical students
Table 6

Results of J-SHI

EDS

non-EDS

P-values

Number33
26
1. I take daytime naps lasting two or more hours.
2.2 ± 1.0
1.0 ± 0.8
＜ 0.001
2. I go to bed at different times from day to day.
2.6 ± 0.9
1.4 ± 0.8
＜ 0.001
3. I get out of bed at different times from day to day.
2.5 ± 0.9
1.4 ± 0.9
＜ 0.001
4. I exercise to the point of sweating within 1 h of going to bed.
0.4 ± 0.6
0.3 ± 0.6
0.563
5. I stay in bed longer than I should two or three times a week.
1.9 ± 1.3
1.5 ± 1.2
0.269
6. I use alcohol, tobacco, or caffeine within 4 h of going to bed or after going to bed.
1.4 ± 1.2
0.6 ± 0.7
0.002
7. I do something that may wake me up before bedtime (e.g., play video games, use the internet, or clean)
3.3 ± 0.9
2.3 ± 1.2
0.002
8. I go to bed feeling stressed, angry, upset, or nervous.
1.3 ± 1.0
0.6 ± 0.7
0.005
9. I use my bed for things other than sleeping or sex (e.g., watch television, read, eat, or study).
2.1 ± 1.2
1.7 ± 1.4
0.382
10. I sleep on an uncomfortable bed (e.g., poor mattress or pillow, too many or not enough blankets).
0.3 ± 0.5
0.3 ± 0.4
0.794
11. I sleep in an uncomfortable bedroom (e.g., too bright, too stuffy, too hot, too cold, or too noisy).
1.1 ± 1.2
0.8 ± 0.9
0.362
12. I do important work before bedtime (e.g., pay bills, schedule, or study).
2.3 ± 1.0
1.2 ± 0.9
＜ 0.001
13. I think, plan, or worry when I am in bed.
2.1 ± 1.2
1.2 ± 0.9
0.003
Total score23.3 ± 5.2
14.4 ± 5.8＜0.001
Values are means ± SD.
Abbreviations : EDS, excessive daytime sleepiness ; J-SHI, Japanese version of Sleep Hygiene Index.

lowed by circadian rhythm disorder (13.3 ％ ), OSA

EDS cannot be obtained only by a questionnaire sur­

(12.1 ％), RLS/PLMD (10.4 ％), and narcolepsy (7.9 ％).

vey. Most studies concerning population-based sur­In the present study, narcolepsy and insomnia wereveys of sleep disorders used the SLEEP-50 question­

also important causes of EDS with prevalence rates

naire17）. It was demonstrated that the agreementof approximately one third that of ISS. In contrast to

between all clinical diagnoses and SLEEP-50-classi­

the study in Jordan, OSA and RLS/PLMD were only

fications was substantial (κ＝0.77), and the SLEEP-50

seen in one student each in the present study. Thereseems able to detect a variety of sleep disorders andmay be ethnic differences in the frequency of sleep

can aid in screening for common sleep disorders in

disorders

5）
15）
16）

. The purpose of the present study

the general population. In the present study, thewas not to determine the prevalence of sleep disor­causes of EDS could not be clarified without PSG andders among medical students. Therefore, the preva­

MSLT in more than 30 ％ of cases. Therefore, PSG

lence of causes of EDS could not be compared withand MSLT are needed to make an accurate diagnosis.

other population-based questionnaire surveys and

The sleep efficiency and the periods of stage N3

also the method used here was different from a ques­

and REM sleep on PSG were significantly increased

tionnaire survey. Accurate diagnosis of the causes ofand the mean sleep latency in MSLT was shorter in

No. 1, 2023

49

Suzuki・Fujimoto・Hazu et al.

the EDS group than the non-EDS group (Table 3).

and show a worse impact of poor sleep on the quali­

The largest proportion of participants in the EDS

ty of life compared to students of law and economics.

group without sleep disturbance during sleep andA systematic review of EDS in medical students

showing greater desire to sleep had ISS (48.5 ％) fol­suggested that the relationship between sleep dura­

lowed by narcolepsy (18.2 ％) and IH (9.1 ％) (Table 2).

tion and sleep quality may predict EDS22）. The times

Therefore, the EDS group showed higher sleep effi­

at which classes start and of bedside learning vary

ciency and shorter sleep latency than the non-EDS

from day to day, which may cause irregular sleeping

group. In addition, the reasons for the longer N3 andhabits. In the present study, J-SHI showed higher

REM periods were as shown in Table 3. A previous

scores in usage of alcohol, tobacco, or caffeine withinstudy showed that when sleep episodes were cur­4 h of going to bed or after going to bed, and feelings

tailed to 4 h for 4 nights, slow-wave sleep in non-of stress, anger, upset, or nervousness when going to

REM sleep was increased by approximately 20 ％ in

bed, which may contribute to the impairment of18）

the first night . Therefore, many students withsleep quality (Table 6). J-SHI also revealed that

EDS, especially ISS and insomnia, did not have suffi­

playing video games and use of social networks incient sleep periods in daily life, and so they had an

bed or before going to bed caused sleep deprivation

increased percentage of slow-wave sleep in the pres­and delayed bedtime in the EDS group. The results

ent study (Table 2). Moreover, the period of REMof the present study suggested the need for further

sleep was longer in the EDS group, especially among

longitudinal studies of the benefits of using a sleep

those with ISS and NA, compared to the non-EDS

diary for students complaining of EDS to guide im­group. It has been demonstrated that the percentage

provement of their lifestyle and sleep hygiene. In

of REM sleep is significantly decreased during thecases in which EDS does not improve, PSG andearly period of sleep deprivation, but rebounds in the

MSLT should be performed.

two recovery nights, especially in the first recovery
night, compared with baseline levels19）.

The present study had two limitations. First, somestudents, especially those with ISS, showed SOREMPIn this study, PSQI scores were higher in the EDS

once or twice during MSLT. NT2 was diagnosed bygroup (Table 5), and 20 students had scores ＞ 6

more than two SOREMPs and shorter sleep latency

points compared to only two in the non-EDS group,＜ 8 minutes on MSLT. There are difficulties in dis­suggesting that 60.6 ％ of participants in the EDS

tinguishing NT2 without cataplexy from ISS andgroup showed poor quality of sleep (data not shown).

IH23）. MSLT must be repeated at regular intervals to

Medical students must get up early to attend classes

confirm stable hypersomnia and allow accurate diag­in the morning, and 52.0 ％ of students sleep for lessnosis of NT2 and IH24）. In the present study, mostthan 7 h per night20） (Table 4). In the present study,

students who showed EDS had inadequate sleep

the mean bedtime was significantly later in the EDS

hygiene. MSLT should be performed after a suffi­group and the total sleep time was shorter althoughcient time to correct inadequate sleep hygiene andthe differences were not significant. However, theshould be repeated. Three students in the EDS group

SDs of bedtime, wake-up time, and total sleep time

who slept over 7 h almost every night, who showed

were significantly greater in the EDS group, sug­no problems on PSG, and had less than two SOREMPs

gesting irregularity of sleep habits, and poor sleep

were diagnosed with IH. However, if they slept morehygiene corresponding to the results of J-SHI (Table 6,

and their EDS recovered, they would not have been

Item No. 2, 3). Some of the students diagnosed withdiagnosed with IH but with ISS. In addition, we didnarcolepsy, SAS, PLMD, insomnia, and IH showed

not measure orexin in cerebrospinal fluid. Second,poor sleep hygiene, which may cause further exag­

the study was cross-sectional rather than longitudi­

21）suggested

nal in design, and so it was not possible to clarify

that medical students have poorer quality of sleepchanges in diagnosis over time. However, in thegeration of EDS. Preišegolavičiūtė et al.

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EDS in medical students

students who complained of EDS, not only a ques­

EDS was ISS, affecting half of the participants, fol­tionnaire survey but also PSG and MSLT are re­lowed by narcolepsy, IN, IH, OSA, DSWPD, andquired to obtain an accurate diagnosis. In the present

PLMD, and the major characteristic of the students

study, over 30 ％ of the medical students had sleep

with EDS was poor sleep hygiene.

disorders that could be diagnosed by PSG and MSLT.
Ⅴ Conclusion

Ⅵ Acknowledgments
We thank the polysomnography technicians andThis survey including PSG and MSLT among medi­
cal students revealed that the most common cause of

medical students who participated in the present
study.

References
1） El Hangouche AJ, Jniene A, Aboudrar S, et al : Relationship between poor quality sleep, excessive daytime sleepinessand low academic performance in medical students Adv Med Educ Pract 9 : 631-638, 2018
2） Zailinawati AH, Teng CL, Chung YC, Teow TL, Lee PN, Jagmohni KS : Daytime sleepiness and sleep quality among
Malaysian medical students. Med J Malaysia 64 : 108-110, 2009
3） Ahmed N, Sadat M, Cukor D : Sleep knowledge and behaviors in medical students : results of a single center survey.
Acad Psychiatry 41 : 674-678, 20174） Kunikata K, Inoue F : Factors affecting dozing during class in university students. School Health Studies (Jap J
School Health, abstract in English) 54 : 62-71, 2012 (in Japanese)5） Gaultney JF : The prevalence of sleep disorders in college students : impact on academic performance. J Am Coll
Health 59 : 91-97, 2010
6） Takegami M, Suzukamo Y, Wakita T, et al : Development of a Japanese version of the Epworth Sleepiness Scale(JESS) based on item response theory. Sleep Med 10 : 556-565, 2009
7） Doi Y, Minowa M, Uchiyama M, et al : Psychometric assessment of subjective sleep quality using the Japaneseversion of the Pittsburgh Sleep Quality Index (PSQI-J) in psychiatric disordered and control subjects. Psychiatry
Res 97 : 165-172, 2000
8） Hara S, Nonaka S, Ishii M, Ogawa Y, Yang CM, Okajima I : Validation of the Japanese version of the Sleep Hygiene
Practice Scale. Sleep Med 80 : 204-209, 2021
9） American Academy of Sleep Medicine. International Classification of Sleep Disorders. 3rd ed. Academy of Sleep
Medicine, Darien, 201410） Mastin DF, Bryson J, Corwyn R : Assessment of sleep hygiene using the Sleep Hygiene Index. J Behav Med
29 : 223-227, 2006
11） American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events, Version
2.1. American Academy of Sleep Medicine, Darien, 201412） Iber C, Ancoli-Israel S, Chesson AL, Quan SF : The American academy sleep medicine manual for the scoring of
sleep and associated events, rules, terminology and technical specifications. Westchester, IL : American Academy
Sleep Medicine ; 2007
13） The Japanese Society of Sleep Research (2010) Narcolepsy Guideline. The Japanese Society of Sleep Research Web.
http://jssr.jp/data/pdf/narcolepsy.pdf (in Japanese). Accessed 8 January 201914） Wang L, Qin P, Zhao Y, et al : Prevalence and risk factors of poor sleep quality among Inner Mongolia Medical
University students : A cross-sectional survey. Psychiatry Research 244 : 243-248, 201615） Yassin A, Al-Mistarehi AH, Beni Yonis O, Aleshawi AJ, Momany SM, Khassawneh BY : Prevalence of sleep
disorders among medical students and their association with poor academic performance : A cross-sectional study.
Ann Med Surg (Lond) 58 : 124-129, 2020
No. 1, 2023

51

Suzuki・Fujimoto・Hazu et al.
16） Kerkhof GA : Epidemiology of sleep and sleep disorders in The Netherlands. Sleep Med 30 : 229-239, 201717） Spoormaker VI, Verbeek I, van den Bout I, Klip EC : Initial validation of the SLEEP-50 questionnaire. Behav Sleep
Med 3 : 227-46, 200518） Jahrami H, Alshomili H, Almannai N, et al : Predictors of excessive daytime sleepiness in medical students. A metaregression. Clocks Sleep 11 : 209-219, 201919） Matsushita M, Koyama A, Ushijima H, et al : Sleep duration and its association with sleepiness and depression in“ronin-sei” preparatory school students. Asian J Psychiatry 9 : 61-66, 201420） Tamura H, Nishida T, Tsuji A, Sakakibara H : Association between excessive use of mobile phone and insomnia anddepression among Japanese adolescents. Int J Environ Res Public Health 14 : 701-711, 201721） Preišegolavičiūtė E, Leskauskas D, Adomaitienė V : Associations of quality of sleep with lifestyle factors and profileof studies among Lithuanian students. Medicina (Kaunas) 46 : 482-189, 201022） Lee J : Sleep duration’s association with diet, physical activity, mental status, and weight among Korean high school
students. Asia Pac J Clin Nutr 26 : 906-913, 201723） Marti I, Valko PO, Khatami R, Bassetti CL, Baumann CR : Multiple sleep latency measures in narcolepsy andbehaviourally induced insufficient sleep syndrome. Sleep Med 10 : 1146-50, 200924） Lopez R, Doukkali A, Barateau L, et al : Test-retest reliability of the multiple sleep latency test in central disordersof hypersomnolence. Sleep. 2017 ; 40. doi : 10.1093/sleep/zsx164（2022. 2. 14 received ; 2022. 9. 12 accepted）

52

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