青森保健医療福祉研究5（1）; 1-10: 2023

Original article

https://doi.org/10.24552/00002211   ©青森県立保健大学

Relationship of preschoolers’ chronotype withparental sleep habits and considerationof sleep behavior
1）

2）

Mitsuko Iwabuchi , Terumi Kogawa

1 ）School of Nursing, Iwate Medical University2 ）Aomori University of Health and Welfare Graduate School of Health Sciences
ABSTRACT［Objective］Chronotypes reflect individual differences in circadian rhythm phases. Studies on children’s
chronotypes, health, and behavior exist; however, the relationship between children’s chronotypes andparental sleep habits remains unknown. Therefore, we aimed to investigate the relationship between thechronotypes of preschool children and their parents’ sleep habits.
［Methods］From October 2020 to November 2020, we conducted a survey on the sleep habits and sleepconscious behaviors of preschool children and their parents in Iwate Prefecture. We used the Japaneseversion of the children’s chronotype questionnaire to investigate morning, intermediate, and evening chronotypes in parents of preschoolers aged 3-5 years. A sleep quality index evaluation sheet was used toassess parents’ sleep patterns. We compared parental sleep habits and sleep-conscious behaviors among
the three chronotypes.
［Results］The morning, intermediate, and evening chronotypes accounted for 24.8％ , 58.6％ , and 16.6％of the children’s chronotypes, respectively. The weekday bedtime, sleep onset time, sleep center time, andweekend wake-up time of parents were related to the central sleep duration on weekends. Parents ofevening-chronotype children demonstrated a post-phase sleep-wake rhythm. They experienced difficulties
in maintaining the motivation necessary to accomplish tasks Moreover, these parents practiced poor
sleeping habits, such as “opening the curtain and permitting light in the morning,” “no television in the
bedroom,” “not excited before bedtime at night,” and “fixed return time while going out with children” inensuring good sleep for their children.
［Conclusions］Medical staff should consider children’s chronotypes and parental lifestyles while providing
health guidance on optimizing sleep and reducing sleep problems in parents and children.

《 Key Words》 c hronotype, preschool children, parent-child relationship, parental sleep habits,
consideration of sleep behavior

Ⅰ．Background
Chronotypes refer to individual differences in thephases of circadian rhythms. Preschool children
tend strongly towards the morning chronotype,which changes to the evening chronotype duringpuberty. The evening chronotype peaks at approxCorresponding author, Dr Mitsuko Iwabuchi（E-mail: iwabuchi@iwate-med.ac.jp）
School of Nursing, Iwate Medical University
1-1-1, Idaidori, Yahabacho, Shiwa-gun, Iwate 028-3694, Japan
Tel: +81-19-651-5110 ext 5416
（Recieved December 21, 2022; Accepted May 31, 2023）

imately 21 years and 19.5 years for boys and girls,
respectively, and subsequently changes to the1）morning chronotype . Therefore, chronotypes
change with age and differ by sex. In modern society, social time and artificial lighting modify sleep
habits, including bedtime and wake-up time on
weekdays and weekends. Following a short sleep
on weekdays, delayed wake-up time on weekends
without social restrictions causes a change in thecircadian rhythm phase of sleep time on weekdays.
Accordingly, in a previous study that used theMunich chronotype questionnaire, chronotype
assessment was based on mid-sleep time on free2）days without social constraints . Late mid-sleep
1

青森保健医療福祉研究5（1）; 1-10: 2023

time on free days indicates the evening chronotype. Social jet lag（SJL）is a condition characterized by a malfunction due to a mismatch between
3）social time and the biological clock . Extreme evenings have been associated with an increased incidence of depression in adults according to previous
4）
5）
studies . A thorough review by Taillard et al.
found a strong association between chronotype andattention-deficit/hyperactivity disorder in adults.
Preschool children with the evening chronotype
manifest greater sleep problems than their morning and intermediate chronotype counterparts, suggesting that chronotype may play a role in early6）
childhood sleep disorders . The evening chronotype is associated with behavioral abnormalities,
such as behavioral problems, which affects peer
7）
relationships in preschool children . Furthermore,antisocial behaviors during childhood and adolescence were more prominent in individuals with theevening chronotype than in those with the morning
8）
chronotype . Researchers have reported a consistent association between short sleep duration in
9）early childhood and obesity . Circadian rhythm
preferences of mothers are associated with thedevelopment of infant circadian rhythms and may
be a potential risk factor for the development of
10）
sleep problems during early childhood . Infants
with different chronotypes have dissimilar bedtime
11）
routines and daily schedules . Parents who know
their children’s sleep patterns are more likely to12）have healthy sleep habits . In addition, parents
with low health literacy may place a television（TV）in the room where their baby sleeps, leading
13）
to poor sleep at night . The evening chronotype isassociated with delayed onset of dim-light melato14）
nin. Moreover, bright nights affect bedtime . The
evening chronotype, associated with sleep deprivation, was observed in 10.0％ of preschool children
15）
in Japan . Small population areas, long TV viewing times, prolonged work schedule for mothers,
and attending kindergarten reduced the total sleep
16）
duration in 4.5-year-old children in Japan . Thesefindings warrant evaluating the lifestyles of children and parents to improve their sleep habits.
Studies have been conducted on children’s chronotypes, sleep problems, behavioral problems, maternal chronotypes, and circadian rhythm development. However, reports on preschool children’s
chronotypes, parental sleep habits, and parental
sleep-conscious behaviors are limited.
Therefore, we aimed to clarify the relationshipbetween preschool children’s chronotype, parental
sleep habits, and parental sleep-conscious behaviors
to close the gap between chronotype and social
2time and ensure appropriate sleep habits.

Ⅱ．Methods
1 ．Participants and data collection
We conducted the research survey at a childcare
center in the suburbs of Japan（Iwate prefecture,N39）. Six childcare center directors, randomly
selected from 72 childcare centers in City A contributed to this study. The participants included
354 parents with primary parenting roles for children aged 3-5 years who were attending six daycare centers. We distributed anonymous, selfadministered questionnaires between October 2020
and November 2020. Consent was obtained from214 participants（recovery rate: 60.5％）.
2 ．Survey items2.1）Attributes
Questions about attributes, including parental
age, parental sex （father or mother）, parental
work status（regular or part-time staff）, child’s age,child’s sex（boy or girl）, child’s birth order, child’sdevelopmental difficulties（yes or no）, and family
structure（nuclear family or extended family）.
2.2）Children’s chronotypes and sleep habits
The children’s chronotype questionnaire（CCTQ）
was used to evaluate differences in phases of circadian rhythms in early childhood and school-goingchildren. The questionnaire comprised 16, 10, andone items related to sleep/wakefulness, morning/
evening type, and chronotype, respectively. For the
sleep/wakefulness-related items, we recorded sleep
habits on scheduled and free days. Questions on
the morning/evening type comprised the degree ofdifficulty in getting up and approximately 30 min
after getting up, the best rhythm（four points）,
and the time when they felt tired and very sleepy.
Answers were provided in three to five stages
with a complete awakening latency. In addition to
the responses on questions related to sleep/wakefulness, answers were provided to questions
related to morning/evening chronotype. Each item
was assigned 1-5 or 1-3 points according to the
CCTQ score calculation method, and the total
score range was 10 – 48 points. The chronotypes
were considered “morning,” “intermediate,” and“evening” for ≦23 points, 24-32 points, and ≧33
points, respectively. The reliability and validity of
17,18）
this scale was confirmed.
19）
Doi et al. developed a Japanese version of the
CCTQ. The Cronbach’s alpha coefficient was set at
0.76 to confirm the reliability and validity of this20）
scale . Correlations were observed among thesleep-wake parameters measured using the JapaneseRelationship of preschoolers’ chronotype with parental sleep habits and consideration of sleep behavior
20）

version of the CCTQ and an actigraph . The
Japanese version of the CCTQ is a self-administered questionnaire that allows for the subjective
assessment of chronotypes in preschool children.
The difference between central sleep times on
21）
weekdays and weekends was defined as SJL .
2.3）Parents’ sleep habits and quality of sleep
The Pittsburgh Sleep Quality Index（PSQI）is a
widely used standardized measure for assessing
subjective sleep quality. We used the Japanese version of the PSQI（PSQI-J）to assess parents’ sleep
22）
quality . PSQI-J is a self-administered questionnaire comprising 18 questions. Self-rated items
were used to generate seven component scores（range of subscale scores: 0-3）for the following
parameters: sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances,use of sleeping medications, and daytime dysfunction. The sum of these scores yielded one global
score for subjective sleep quality（range, 0-21）,
with higher scores representing poorer subjective
sleep quality. The cut-off value was set at 5.5
points, and a score ≧5.5 points indicated poor
sleep. The Cronbach’s alpha factor was set at 0.77
to confirm the reliability and validity of the scoresaccording to a study that compared psychiatric23）
patients and healthy individuals . PSQI-J allows forthe subjective assessment of sleep quality. Furthermore, differences in sleep time on weekdays andweekends were assessed using a question with
Yes/No answer. When the answer was “Yes”, werequested the participants respond to “weekend
wake-up time,” “weekend bedtime,” and “weekend
sleep onset time.” SJL referred to the median sleep
time zone and median sleep time, and was calculated as the difference between the central sleep
time on weekdays and weekends. In addition, werequested that the parents answered Yes/No ifthey experienced sleep habits different from that of
their infants.
2.4）Children sleep-habit conscious behavior
The items for behaviors that affected children’s
sleep were created with reference to the original
13,24）
25）and environmental factors
lifestyle-related
that affect sleep. Factors affecting sleep included
breakfast, caffeine intake, and media use as lifestylefactors, and light and bedroom environments asenvironmental factors. The participants wererequested to answer Yes/No for the following
items: “regular breakfast consumption,” “fixed place
to sleep at night,” “fixed wake-up time,” “opening
the curtains and permitting light in the morning,”,“spending the day in a bright place,” “fixed return
time while going out with children,” “fixed dinnertime,” “not consuming caffeinated beverages（carbonated drinks and coffee）3 h before bedtime,”“no smartphone or tablet use within 1 h before
bedtime,” “not excited before bedtime at night,”“fixed place to sleep at night,” “dark bedroom,” “noTV in the bedroom,” and “staying awake until thechild falls asleep.”
3 ．Statistical analysis
Based on the CCTQ classification of children, we
compared the chronotypes using three groups asfollows: morning, intermediate, and evening. Parents’ insomnia, use of sleeping pills, and obstacles
to daily life were compared between the “none”
and other groups. Parental sleep quality was classified as “good” or “bad.” We performed Fisher’s
2
exact and χ tests to assess parental sleep difficulties, use of sleeping pills, disturbances in daily life,
sleep quality, and discrepancies in sleep habits
between children and parents.
We performed residual analysis to determine
significant differences between the three chronotypes. Regarding the sleep habits of the children andtheir parents, we performed the Kruskal – Wallis test
and one-way analysis of variance （ANOVA） for
variables with and without confirmed normality,
respectively. To determine significant differences in
the one-way ANOVA, we conducted multiple comparisons（Bonferroni-Dunn method, Tukey’s method）.
To compare sleep time on weekdays and weekends, t-test and Wilcoxon signed-rank test were
performed for variables with and without normality, respectively. IBM SPSS Statistics ver.27.0 for
Windows（IBM, Tokyo, Japan）was used for statistical analysis, and the significance level was set
at ＜5 ％（two-sided test）.
4 ．Ethical considerations
Participants were provided with written explanations concerning the purpose of the study, theirright to withdraw from participation, an assuranceof anonymity, and publication of the results. The
participants were advised that they were notobliged to answer any questions they felt uncomfortable answering, as they may have been preoccupied with their parental responsibilities during
the survey period. Written and verbal requests
were made to the directors of the daycare facilities
to ensure that there was no children participation
without parental consent. This research procedure
was approved by the research ethics committee ofthe Aomori University of Health and Welfare（approval number: 20001）.

3青森保健医療福祉研究5（1）; 1-10: 2023

Child’s sex

Boy
Girl

76
81

48.4
51.6

Birth orderFirst（non-sibling）
First
Other than first

44
41
72

28.0
26.1
45.9

Anxiety in children

Yes
No

11
146

7.0
93.0

Family structure

Nuclear family
Extended family
Others

131
23
   3

83.4
14.6
1.9

4

＊＊
＊＊

M＜I

M＜E

＊＊

I＜E

＊

I＜E

＊＊

M＜I

M＜E

＊＊

＊

I＜E
＊＊
I＜E

＊＊
＊＊

M＜I
M＜E
＊＊
＊＊
M＜I
M＜E

＊＊

＜.001
＊＊
＜.001
.286
＊＊
＜.001
.778
＊＊
＜.001
.284
1：11
1：06
0：12
1：10
1：28
0：55
0：21
8：00
22：00
0：12
22：22
9：20
2：53
0：19
0：45
0：46
0：23
0：54
0：57
0：40
0：17
8：00
21：57
0：22
22：25
9：23
3：07
0：19
1：00
0：45
0：20
0：44
0：51
0：31
0：20
7：30
21：30
0：19
22：00
9：25
2：37
0：15
0：37
0：34
0：14
0：34
0：44
0：24
0：13
7：31
21：15
0：20
21：54
9：24
2：36
0：18

＊＊
＊＊

M＜I

M＜E

＊＊

I＜E

＊

I＜E

＊＊

M＜I

M＜E

＊＊

＊＊
＊＊
＊＊

M＜I
M＜E
＊＊
＊＊
M＜I
M＜E

＊＊

＜.001
＊＊
＜.001
.166
＊＊
＜.001
.772
＊＊
＜.001
0：40
1：18
0：10
1：00
1：01
0：38
7：15
21：50
0：15
22：20
9：07
2：53
0：28
0：46
0：23
0：51
0：51
0：33
7：13
21：48
0：21
22：21
9：06
2：54
0：35
0：30
0：20
0：30
0：48
0：28
6：45
21：10
0：20
21：54
9：11
2：23
0：29
0：28
0：14
0：28
0：36
0：22
6：47
21：18
0：22
21：50
9：06
2：24

Post hoc p-value
p-value
Evening chronotype（n＝26）
MeanSD
medianIQR

SD: Standard deviation; IQR: Interquartile range; SJL: Social jet lag; M: Morning chronotype; I: Intermediate chronotype; E: Evening chronotype.
†
Kruskal – Wallis test（Multiple comparison: Bonferroni-Dunn method）; : ANOVA（Multiple comparison: Tukey method）.
＊＊＊: p＜.05, : p＜.01.

19.1
53.5
27.4

1：00
1：00
0：13
0：40
1：05
0：50
0：24

30
84
43

7：00
21：00
0：15
21：30
9：10
2：02
0：09

3 years
4 years
5 years

0：41
0：41
0：09
0：39
0：45
0：34
0：14

Child’s age

6：53
20：59
0：15
21：21
9：18
2：01
0：15

59.2
31.8
8.9

0：40
0：45
0：20
0：40
0：50
0：34

93
50
14

6：30
21：00
0：15
21：20
9：10
1：55

RegularNon-regular
Others

0：30
0：36
0：10
0：34
0：34
0：26

Employment

6：25
20：53
0：18
21：16
9：12
1：52

％

Weekday
Wake up time
BedtimeSleep latency
Sleep onset†
Sleep period†
Midsleep point
Weekend
Wake up time
BedtimeSleep latency
Sleep onset†
Sleep period
Midsleep pointSJLnIntermediate chronotype（n＝92）
MeanSD
MedianIQR

Table 1. Participants’ characteristics

Morning chronotype（n＝39）
MeanSD
MedianIQR

2 ．Children’s chronotypes
There were 39 （24.8％）, 92 （58.6％）, and 26（16.6％）CCTQ-classified morning, intermediate,
and evening chronotypes, respectively. Table 2
summarizes the sleep habits of children according
to their chronotypes. There were significant differ-

Table 2. Child sleep-wake rhythm according to the chronotypes

1 ．Parent and child characteristics
Data of 157 parent and child dyads were analyzed without missing values（valid response rate:
45.8％）. Table 1 presents an outline of the participants’ characteristics. Parents who responded
comprised 156 mothers （99.4％） and one father（0.6％）, with an average age of 35.6 years（SD＝4.8 years）. The working conditions included 93（59.2％）, 50 （31.9％）, and 14 （8.9％） full-time,
part-time, and other employees, respectively. Others
were self-employed, unemployed, or on childcare
leave. The children included 76 boys（48.4％）and
81 girls（51.6％）. The average age of the children
was 4.6 years（SD＝0.6 years）, with 30（19.1％）,
84（53.5％）, and 43（27.4％）children aged 3, 4,
and 5 years, respectively. The birth order was
44 （28.0％）, 41 （26.1％）, and 72 （45.9％） for
children without siblings, younger brothers andsisters, and second and subsequent children, respectively. Eleven（7.0％）children developed anxiety.
The family structure comprised 131 （83.4％）,
23（14.6％）, and three（1.9％）nuclear families,
extended families, and single-parent households,
respectively.

I＜E
＊＊
I＜E

Ⅲ．Results

＊

M＜E

＊

M＜E

＊

.044
.155
.155
.115
.876
＊
.013
.773
.060
1：48
1：07
0：20
1：11
2：13
1：07
0：45
3
7：30
23：30
0：20
23：47
7：47
3：35
0：39
6.0
1：09
1：16
0：18
1：16
1：10
1：03
0：37
2.7
7：16
23：21
0：23
23：45
7：30
3：30
0：42
6.35
1：30
2：00
0：20
2：00
1：59
1：18
1：13
4
7：00
23：00
0：26
23：17
7：27
3：14
0：36
5.0
0：58
1：14
0：24
1：11
1：14
0：54
0：41
3.0
6：57
22：59
0：27
23：26
7：30
3：11
0：42
5.64
1：19
2：30
0：20
2：05
1：39
1：32
1：05
4
1：00
1：18
0：24
1：18
1：16
0：59
0：35
3.0
6：37
22：37
0：22
22：59
7：38
2：48
0：36
4.82

7：00
23：00
0：15
23：10
7：45
2：50
0：30
5.0

.080
＊
＊
＊
.038
M＜E
I＜E
.367
＊
＊＊
＊
M＜E
I＜E
.030
.349
＊＊
＊＊
＊
.008
M＜E
I＜E
0：30
1：52
0：20
1：25
1：01
0：37
6：15
23：00
0：20
23：30
6：47
2：51
0：33
1：07
0：16
1：04
1：07
0：38
6：10
23：01
0：22
23：24
6：46
2：47
1：00
1：00
0：20
1：22
1：18
0：53
6：00
22：30
0：20
23：00
7：04
2：30
0：44
1：04
0：18
1：01
1：08
0：41
6：04
22：33
0：25
22：59
7：05
2：31
0：45
1：40
0：20
1：35
1：45
0：57
6：00
22：00
0：15
22：55
7：04
2：17
0：38
1：08
0：22
1：07
1：05
0：44
5：50
22：17
0：22
22：39
7：10
2：15

Weekday
Wake up time
BedtimeSleep latency
Sleep onset†
Sleep period
Midsleep point
Weekend
Wake up time
BedtimeSleep latency
Sleep onset
Sleep period†
Midsleep point
SJl
PSQI

p-value
Evening chronotype（n＝26）
MeanSD
medianIQRIntermediate chronotype（n＝92）
MeanSD
MedianIQR

SD: Standard deviation; IQR: Interquartile range; SJL: Social jet lag; PSQI: Pittsburgh Sleep Quality Index; M: Morning chronotype; I: Intermediate chronotype; E: Evening chronotype.
†
Kruskal – Wallis test（Multiple comparison: Bonferroni-Dunn method）; : ANOVA（Multiple comparison: Tukey method）.
＊＊＊: p＜.05, : p＜.01.

4 ．Children sleep-habit consciousness behavior
Table 5 summarizes the sleep-conscious behav-

Morning chronotype（n＝39）
MeanSD
MedianIQR

3 ．Children’s chronotype and parental sleep quality
Table 4 summarizes parental sleep problems
according to their children’s chronotype. Approximately 80.8％ of the parents of evening-chronotype children had a high percentage of problems
related to adequate enthusiasm（p＝.008）. There
were no significant differences in sleep difficulty,
use of sleeping pills, drowsiness, sleep quality, or
PSQI-J scores. Approximately 15.4％, 18.5％, and34.5％ of parents experienced differences in their
sleep habits and those of their children for themorning, intermediate, and evening chronotypes,
respectively, without significant differences（p＝.132）.

Table 3. Parental sleep-wake rhythm according to children’s chronotype

ences in weekday wake-up time（p＜.001）, weekday bedtime（p＜.001）, weekday sleep onset time
（p＜.001）, weekday central sleep time（p＜.001）,
weekend-day bedtime（p＜.001）, weekend-day sleep
onset time（p＜.001）, and weekend-day mid-sleeptime（p＜.001）. In particular, the mid-sleep timewas 2:54 on weekdays, which was later than thatof the morning and intermediate types（1:52 and
2:24, respectively; p＜.001）. There were no significant differences between the time taken to fallasleep on weekdays and that to fall asleep on
weekends. Similar results were obtained for sleep
time and SJL.
Table 3 summarizes the sleep habits of theparents according to their chronotypes. For parents, weekday bedtime（p＝.038）, weekday sleep
onset time（p＝.030）, weekday sleep central time
（p＝.008）, weekend wake-up time（p＝.044）, andweekend sleep central time（p＝.013）were significantly different as parental weekend day was 3:30
for evening-time children. This was significantly
slower than that of the morning chronotype of 2:48
（p＝.027）.
A chronotype-based comparison of the sleeping
hours of children and their parents on weekdays
and weekends revealed that the sleeping hours ofchildren with intermediate chronotype were 9:06
and 9:24 on weekdays and weekends, respectively,
which differed significantly （p＜.001）. However,there was no significant difference in sleep duration between children with morning and evening
chronotypes（p＝.267 and p＝.070, respectively）. We
observed a significant difference in parental sleep
time between weekdays and weekends （morning
chronotype, p＝.029; intermediate chronotype, p＜.001;
and evening chronotype, p＝.009）.

Post hoc p-value

Relationship of preschoolers’ chronotype with parental sleep habits and consideration of sleep behavior

5青森保健医療福祉研究5（1）; 1-10: 2023

Table 4. Parental sleep problems†

Cannot fall asleep within 30 min
Wake up in the middle of the night or early morning
Wake up to use the bathroom†
Cannot breathe comfortably†
Cough or snore loudly†
Feel extremely cold†
Feel extremely hot
Had bad dreams†
Experience pain†
Consume sleeping pills
Have trouble staying awake††
Have adequate enthusiasm†††
Overall sleep quality§
PSQI score

Morning
chronotype（n＝39）

Intermediatechronotype（n＝92）

Evening
chronotype（n＝26）

n

％

n

％

n

％

16
24
17
3
4
5
2
8
6
0
8
17
12
16

41.0
61.5
43.6
7.7
10.3
12.8
16.7
20.5
15.4
0.0
20.5
43.6
30.8
41.0

49
57
38
2
4
14
8
15
8
4
30
46
36
42

53.3
62.0
41.3
2.2
4.3
15.2
66.7
16.3
8.7
4.3
32.6
50.0
39.1
45.7

14
15
12
0
2
2
2
4
2
1
11
21
12
18

53.8
57.7
46.2
0.0
7.7
7.7
16.7
15.4
7.7
3.8
42.3
80.8
46.2
69.2

p-value

.408
.924
.899
.161
.390
.605
.914
.814
.468
.450
.161
＊＊
.008
.440
.059

†

: Answer choices; past month, ＜once a week, once or twice a week, ≦thrice a week.
: Answer choices; moderate problem, somewhat a problem, big problem.
†††: Answer; fairly good, fairly bad, very bad.
§: ＞5.52**: p＜.01（Fisher’s exact test, χ test）††

Table 5. Parental sleep-conscious behaviors according to children’s chronotypes＊

Regular breakfast consumption＊
Fixed place to sleep at night＊
Dark bedroom
Spend the day in a bright place
Staying until the child falls asleep
Opening the curtains and permitting light in the morning
Fixed dinner time
Fixed wakeup time
No television in the bedroom
Not consuming caffeinated beverage 3 h before bedtime
Taking a nap on holidays
No media use within 1 h before bedtime
Not excited before bedtime at night
Fixed return time while going out with children＊: p＜.05;＊＊

Intermediatechronotype（n＝92）

Evening
chronotype（n＝26）

n

％

n

％

n

％

39
39
36
33
34
34
29
26
29
20
28
18
22
16

100.0
100.0
92.3
84.6
87.2
87.2
74.4
66.7
74.4
51.3
71.8
46.2
56.4
41.0

88
88
88
81
78
78
65
64
64
65
38
49
46
24

95.7
95.7
95.7
88.0
84.8
84.8
70.7
69.6
69.6
70.7
41.3
53.3
50.0
26.1

24
23
22
18
20
17
20
14
12
13
11
7
6
3

92.3
88.5
84.6
69.2
76.9
65.4
76.9
53.8
46.2
50.0
42.3
26.9
23.1
11.5

p-value

.192
.055
.125
.068
.520
＊
.047
.786
.326
＊
.042
＊
.040
＊＊
.005
.059
＊
.021
＊
.030

2

: p＜.01（χ test, Fisher’s exact test.）iors of parents according to their children’s chronotypes. In the evening chronotype, the percentage of“Yes” responses for “opening the curtains and permitting light in the morning,” “no TV in the bedroom,” “not excited before bedtime at night,” and“fixed return time while going out with children” was
65.4％（p＝.047）, 46.2％（p＝.042）, 23.1％（p＝.021）,
and 11.5％（p＝.030）, respectively. The intermedi6

Morning
chronotype（n＝39）

ate chronotype demonstrated a high percentage（75.7％ , p＝.040）of those who stopped consuming
caffeinated beverages（carbonated beverages andcoffee）within 3 h of bedtime. There were no significant differences in regular breakfast consumption, fixed supper time, smartphone and tablet
screens turned off within 1 h before bedtime, fixed
wake-up time, spending time in a bright place dur-

Relationship of preschoolers’ chronotype with parental sleep habits and consideration of sleep behavior

ing the day, or fixed sleeping place at night. There
was no significant difference in the percentage of
respondents who kept their bedrooms dark andquiet and were on their sides until they fell asleep.

Ⅳ．Discussion
In this study, we investigated the relationshipbetween parental sleep habits and sleep-conscious
behavior according to their children’s chronotypes.
Sleep habits and sleep-conscious behaviors differedamong parents depending on their children’s chronotypes. Parents of evening-chronotype children
showed late central sleep time on weekdays andweekends, in addition to late bedtime, sleep on
weekdays, and waking up on weekends. Thus, thesleep habits of evening-chronotype children andtheir parents were related, suggesting a regressedcircadian rhythm phase. There were 24.8％,
58.6％, and 16.6％ morning, intermediate, andevening-chronotypes children, respectively. The
proportion of children with the evening chronotype
tended to be slightly higher than that reported by15）
Doi （10.0％）. In a study involving Japanese participants（aged 20-79 years）, there was no clear
seasonal variation in sleep onset time; however,there was seasonal variation in waking time, with26）
the most recent peak recorded in winter . Sleep
duration was found to be the longest in the winter27）
and shortest in the summer（age 15-79 years） .
This present study was conducted during the latefall period. Therefore, the late sleep-wake rhythmof parents and their children with evening chronotypes may have regressed.
Late sleep by parents and “going out after 20:00”
28）
affect children’s bedtime . Moreover, children’s
bedtimes have been shown to be positively related
to their mother’s return from work and dinner
29）
16）
times . Ikeda et al. reported the association
between children’s bedtime and their mothers’ long
working hours. The participants in this study were
employed and their children attended childcare
15）
centers. However, Doi et al. included kindergarten and childcare center children, and higher evening-chronotype children in this study were supposedly affected by their mothers’ working hours.
The evening chronotype has been associated3）with substantial SJL . However, in the present
study, there was no difference in the sleeping hoursof parents on weekdays and weekends among themorning, intermediate, and evening chronotypes. In
addition, the SJL of the parents was 30, 36, and 39
min for the morning, intermediate, and evening
chronotypes, respectively, with no significant difference. This difference is believed to be attributed tothe children’s adjustment to their parents’ sleep
patterns. Parents of children with an eveningchronotype tend to prioritize securing sufficient sleep
time by going to bed and waking up late. Parents ofevening-chronotype children indicated that their
sleep-wake rhythms were in the post-phase. Thismay have caused problems in sustaining the drive
required to accomplish tasks. Thus, sleep-conscious
behaviors that can be improved through evening
chronotype sleep habits should be advocated.
For sleep-conscious behavior, the rate of bedroom darkening was high for all chronotypes, with
non-significant differences. However, for the evening chronotype, the rate of “not placing a TV in
the bedroom” was 46.2％（p＝.042）, that of “notexcited before going to bed” was 23.1％（p＝.021）,
and that of “fixed return time while going out withchildren” was as low as 11.5％（p＝.030）. There
was no significant difference in the percentage ofparticipants who stopped utilizing multimedia
devices before going to bed, although this percent16）
age was as low as 26.9％. Ikeda et al. reported
that long game and TV viewing times promoted
29）
late bedtime in children. Hattori et al. reported
that the bedtime of a child is related to their TV
or video viewing time from dinner to bedtime.
Melatonin secretion has been shown to be suppressed in children who receive light stimulation at30）
31）
night . Other studies have suggested that melatonin secretion, which is more sensitive to light, issuppressed more by night light in elementary
school children than in adults. Our findings revealed
that the circadian rhythm was in the late phasebecause of habitual night light and stimulation.
Furthermore, the proportion of those involved inbrightening of the room in the morning was as low
as 65.4％ among those with the evening chronotype（p＝.047）. Moreover, their median wake-up times（median）was 7:15（p＜.001）and 8:00（p＜.001）onweekdays and weekends, respectively. Exposure tostrong light in the morning has been shown to32）
accelerate the onset of melatonin secretion . Considering the cross-sectional design of this study, thedetailed causal relationship is unknown. However,the findings indicate that children’s chronotypes
may be determined by their parents’ sleep consideration. Therefore, parents should be aware of
their children’s sleep habits.
Sleep habits on free days without time constraints reflect an individual’s body clock and should
be adapted to the individual’s chronotype as much3）
as possible . The development of individual differences in adolescent circadian rhythms begins in
33）
34）
mid-childhood . In secondary schools in Singapore
7青森保健医療福祉研究5（1）; 1-10: 2023
35）

and in high schools in the United States , efforts
are being made to delay school start times andreduce SJL to ensure sufficient sleep on weekdays.
This in turn secured children’s sleep time andimproved their drowsiness and health conditions.
Such efforts are being proposed in early childhood
to minimize the gap between the chronotype andsocial clock; therefore, sleep habits should be
adjusted to a sleep-wake phase（morning type）, in
addition to moderate adjustment in social clock36）（going to kindergarten considerably late） . In ourstudy, 34.5％ of parents experienced different
sleep habits compared to their children（evening
chronotype）. Parents of evening-chronotype children are likely to face difficulties falling asleep andwaking up. These findings warrant supporting parents to adjust the light environment in the morning and evening for their children and recognize
the need to advance the sleep-wake phase of thecircadian rhythm.
Our study had some limitations. First, this was across-sectional study that could not determine any
effects between the variables. Second, the prevalence of the coronavirus disease 2019 supposedly
caused changes in family life patterns, such as
parental work styles and school closures. Third, thestudy’s sample size was limited, necessitating careful consideration of its generalization. However, as
there are few reports on parental sleep habits andsleep-conscious behaviors according to the CCTQbased chronotype classification of children, thisstudy is significant because its findings will facilitate the accumulation of such data.

Ⅴ．Conclusions
The sleep habits of parents of evening-chronotype children were slower than those of morningand intermediate-type children. Second, they demonstrated a post-phase circadian rhythm. Third, it
was difficult to continuously motivate them. Finally,
they did not practice the habit of ensuring good
sleep for their children. These findings prompt forthe consideration of the chronotype of children andthe social time of their parents.

Conflict of Interest Statement
The authors declare that they have no conflict ofinterests.

Sources of Funding
This study was supported by Grant-in-Aid for
Scientific Research（C）（Grant No.20K10999）.

8

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青森保健医療福祉研究5（1）; 1-10: 2023

原著論文

幼児のクロノタイプと親の睡眠習慣，睡眠配慮行動との関連
1）

岩渕光子 ，古川照美

2）1）岩手医科大学看護学部
2）青森県立保健大学大学院健康科学研究科（2022年12月21日受付：2023年 3 月31日受理）

抄録〔目的〕 クロノタイプは，概日リズムの位相の個人差を表している。これまで幼児のクロノタイプと幼児の健康や行動に関連する研究は報告されているが，親の睡眠習慣との関連についてはよくわかっていない。
本研究では，幼児のクロノタイプと親の睡眠習慣の関連について調査することを目的とした。
〔方法〕 2020年10月～11月にかけて，岩手県の幼児とその親の睡眠習慣と睡眠に配慮した行動に関する調査を実施した。3～5歳児の親を対象に，子どもの朝型―夜型質問票日本語版（CCTQ）を用い朝型，中間型，夜型のクロノタイプを調べた。睡眠の質評価票を用いて，親の睡眠状態を評価した。3つのクロノタイプ間で，親の睡眠習慣，睡眠に配慮した行動を比較した。
〔結果〕 未就学児の朝型，中間型，夜型はそれぞれ24.8％，58.6％，16.6％を占めた。親の平日就床時刻，
平日入眠時刻，平日睡眠中央時刻，週末起床時刻，週末中央睡眠時間は未就学児のクロノタイプと関連がみられた。夜型児の親の睡眠相は後退していた。また，物事をやり遂げるために必要な意欲を維持するのが困難であった。さらに，未就学児の良い睡眠を確保するための，朝はカーテンを開ける，寝室にはテレビを置かない，夜寝る前は興奮させない，外出時は帰宅時刻を決めていることなどの睡眠習慣の実践が不十分であった。
〔結論〕 専門家は幼児のクロノタイプと親のライフスタイルを考慮しながら，親子で最適な睡眠を確保し，睡眠問題の軽減のための保健指導をすることが必要である。
Aomori J. Health Welfare, 5（1）; 1-10: 2023
Key words: クロノタイプ，幼児，親子関係，親の睡眠習慣，睡眠配慮行動
連絡先
岩渕光子（E-mail: iwabuchi@iwate-med.ac.jp）
岩手医科大学看護学部
岩手県紫波郡矢巾町医大通1-1-1
Tel: 019-651-5110（内線5416）

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