Review Reports - Characteristics and Transition of Sleep–Wake Rhythm in Nursery School Children: The Importance of Nocturnal Sleep

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID:

Title: "Characteristics and transition of sleep-wake rhythm during nursey school children and sleep hygiene guidance"

The aim of this work was to describe the sleep-wake changes during nursey school. To this aim, more than 4000 participants were observed for two consecutive weeks by sleep log. Results are descriptive only.

The manuscript is interesting. The strengths are mainly two: the large sample size; having considered sleep from a circadian perspective and not only nighttime sleep.

I have only few suggestions.

I suggest using the term bedtime instead of sleep onset time. Sleep onset time refers to the sleep latency therefore is a little bit confusing.

Considering the descriptive feature of the work, the discussion section could be shortened.

I consider a bit risky to conclude by referring to maintaining balanced mental/physical development, because I don't think it has been measured.

It might be appropriate to discuss some limitations such as the fact that all the data are self-reported and, therefore, not objective.

Author Response

Point-by-point response to Comments and Suggestions for Authors

Comments 1: I suggest using the term bedtime instead of sleep onset time. Sleep onset time refers to the sleep latency therefore is a little bit confusing.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have changed sleep-onset time to bedtime.

Comments 2: Considering the descriptive feature of the work, the discussion section could be shortened.

Response 2: Agree. We have, accordingly worked to make the discussion part compact. We tried to shorten the discussion section, but it may have ended up being longer because we took into consideration the reviewers' opinions. This is due to our lack of ability. We apologize for that. Please comment again if insufficient, with the revised version.

Comments 3: I consider a bit risky to conclude by referring to maintaining balanced mental/physical development, because I don't think it has been measured.

Response 3: We have removed the word "balanced" from the text. The text states that a disruption in daily rhythms can cause imbalances in mental and physical development, and we believe that this is a proposal to bring children's mental and physical development closer to balance through lifestyle guidance.

Comments 4：It might be appropriate to discuss some limitations such as the fact that all the data are self-reported and, therefore, not objective.

Response 4: I have written the following sentences in the discussion (line 158-168). I don't have any other good excuses, so I hope this will be accepted.

“On the other hand, it was pointed out that sleep records of children reported by their guardians could be less accurate than the records by an actigraphy and the sleep time recoded by parents was longer (by 24 to 45 min) than that by an actigraphy [17-19]. However, in another study, sleep record tables were considered clinically useful enough with recognition of the shortcoming [20,21].Indeed, in our previous study, we observed that the actigraphy judged motionless subjects as sleeping and recorded longer sleep times than the actual sleep time. In Japan, it is common for guardians (mainly parents) to share a bedroom with their infants and young children, and it is estimated that such parental observations are relatively more accurate. According to these factors, it is conceived that the use of sleep record charts in clinical settings is meaningful enough at this time.”

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted article examines the sleep patterns of children in Tokyo, Japan using a self reported instrument administered to parents. While the data collected is interesting and extensive, the article should undergo major revisions to be considered for publication.

Major Revisions:

1) The introduction is written far to casually in style. Ex. "The nursery staffs recently concern that quite number of children attending nurseries 33 cannot easily start their daily routines,.." Is the author talking about a specific nursery staff or are their published surveys that can be referenced for these ideas. There should be editing of the writing to follow a more scientific formula, a review of the literature without personal anecdotes. Additionally, the final paragraph should include a synopsis of the hypothesis and the experiments conducted in the study in greater detail.

2) Methods: There needs to greater detail about the administration of the survey and the inclusion of an example of the documents provided to the parents. Some statistics about the number of individuals approached and the completion rates would provide feasibility for prospective other future studies. The authors complete a monumental amount of data collection and understanding how much was successfully completed should be beneficial.

3) In both the Results and Methods, the authors need to select one way to divide the sections, [TITLE], Numbers with parathesis (1)), and numbers followed by titles (2.2 TITLE) are all used though out the sections. There needs to be consistency.

4) In the results, there are redundancies that could be streamlined are tables and graphs needed. Consider box and whisker plots if there is an interesting difference that needs both graphs and ranges. The keys for the figures are also sometimes difficult to decern (ex. figure 2 the boxes are too small to see the patterns clearly). Also, why were no other comparisons made in terms of performance or other demographics. The data collected is so large even doing geospatial statistics with SES would be amazing. There is some interesting sleep and light pollution data examining a similar vein. A statistician should be consulted to make more robust investigations if possible.

Comments on the Quality of English Language

In terms of the English quality, while the sentences are understandable and the ideas communicated well on a layman level. The standards for science writing are higher and often too casual of language is used in the manuscript. One example from the introduction was included above in the general comments. Another example from the methods "We intended to study about all the young children aged from 2 months to 6 years and 7 months who were attending, in 2013, 2014 and 2016, the licensed nurseries, nurseries authorized by Tokyo Metropolitan Government, in-hospital childcare centers and corpo-467 rate nurseries operated by A-Childcare Corporation (ACC)." If you look at other sleep studies they are exact in their language about their participants-Markovic, A., Kaess, M., & Tarokh, L. (2020). Gender differences in adolescent sleep neurophysiology: a high-density sleep EEG study. Scientific reports, 10(1), 15935. , "Thirty-one girls (mean age = 12.13; SD = 1.67) and thirty boys (mean age = 12.83; SD = 0.75) between 9 and 14 years old (84% between 12 and 14 years) were recruited as part of a twin study examining the heritability of the sleep EEG."

Author Response

Response to Reviewer 2 Comments

Comment 1:The introduction is written far to casually in style. Ex. "The nursery staffs recently concern that quite number of children attending nurseries 33 cannot easily start their daily routines,.." Is the author talking about a specific nursery staff or are their published surveys that can be referenced for these ideas. There should be editing of the writing to follow a more scientific formula, a review of the literature without personal anecdotes. Additionally, the final paragraph should include a synopsis of the hypothesis and the experiments conducted in the study in greater detail.

Response 1: Thank you for pointing this out. I agree with this comment. Therefore, I have deleted the sentences, [Paragraph "The staff at the nursery school have recently become concerned that a significant number of children attending the nursery school are having difficulty starting their daily lives smoothly..."], and following sentences were added (line 35-52).

“It is widely recognized that adequate sleep is especially important for children.　There has been excellent report published about the appropriate duration of sleep per day for children need and the authors also emphasizes the importance of sleep on a regular basis, which is associated with better health outcomes including: improved attention, behavior, learning, memory, emotional regulation, quality of life, and mental and physical health. [1]. Generally, when discussing children's sleep problems, the main focus has been on "insufficient sleep" by focusing on the total sleep duration per day and there have been few reports that focus on nighttime sleep duration or chronobiological rhythms. However, it has been reported recently that nighttime sleep, among the total amount of sleep, has a significant impact on children's mental and physical development [2-4], which is expected to bring about a major advance in future research into children's sleep problems. Incidentally, reports on infants' nighttime sleep duration indicate that a continuous sleep rhythm of about 8 to 12 hours is established by the time they are 6 to 7 months of age [5,6]. One of the authors has also been continuing research into the importance of sleep-wake rhythms in the lives of infants and young children, and has reported that ensuring nighttime sleep duration (called Nighttime Basic Sleep Duration=NBSD) and regularity in daily rhythms are particularly important for children's mental and physical development [7].”

Comment 2:

Methods: There needs to greater detail about the administration of the survey and the inclusion of an example of the documents provided to the parents. Some statistics about the number of individuals approached and the completion rates would provide feasibility for prospective other future studies. The authors complete a monumental amount of data collection and understanding how much was successfully completed should be beneficial.

Response 2: The explanation for recipients is quite long and it would be difficult to post the entire thing or provide an excerpt, so we limited it to saying, "We explained that this information is important for supporting children's physical and mental development."

(Line 370-384)

“The significance of the sleep survey was explained to the guardian, and they were invited to participate voluntarily. The data of sleep wake state was obtained using a sleep log form in which cells representing every 30 minutes in 24 hours were filled out to record sleep time continuously for two weeks. The sleep log forms were handed to the guardians before starting the sleep measurement and they were asked to fill the form to record the sleep wake state of their children at home for two weeks. The sleep wake state of the children at nurseries were recorded by the staff and the record was transcribed to their sleep log forms after the sleep measurement period.

The birth dates of the subject children and the names of the nurseries where they were attending were recorded as the basic data. There were 7539 applicants, but records with insufficient information were excluded and data from 4881 children were analyzed.”

Comments 3: In both the Results and Methods, the authors need to select one way to divide the sections, [TITLE], Numbers with parathesis (1)), and numbers followed by titles (2.2 TITLE) are all used though out the sections. There needs to be consistency.

Response 3: We tried it clear. Please comment again, if necessary, with the revised version.

Comments 4-1: In the results, there are redundancies that could be streamlined are tables and graphs needed. Consider box and whisker plots if there is an interesting difference that needs both graphs and ranges. The keys for the figures are also sometimes difficult to decern (ex. figure 2 the boxes are too small to see the patterns clearly).

Response 4-1:

We created “a box and whisker plots” according to your suggestion. (Fig 1 and 2)

Comments 4-2:Also, why were no other comparisons made in terms of performance or other demographics. The data collected is so large even doing geospatial statistics with SES would be amazing. There is some interesting sleep and light pollution data examining a similar vein.

A statistician should be consulted to make more robust investigations if possible.

Response 4-2:

Regarding geospatial statistics and the relationship between sleep and light pollution, we need to collect additional data and it would be a large-scale study, so we will consider it as a topic for future study.

Comments 5: Comments on the Quality of English Language

Response 5: Thank you for your comments and advice regarding English composition.

Methods:　First paragraph “We intended to study about all the young children aged from 2 months to 6 years and 7 months who were attending, in 2013, 2014 and 2016, the licensed nurseries, nurseries authorized by Tokyo Metropolitan Government, in-hospital childcare centers and corpo-467 rate nurseries operated by A-Childcare Corporation (ACC)." was deleted. and replaced following : (line 367-377) “The study was conducted on infants aged 2 months to 6 years and 7 months who attended licensed daycare centers, Tokyo Metropolitan certified daycare centers, hospital daycare centers, and corporate daycare centers operated by A-Childcare Co., Ltd. (ACC) in 2013, 2014, and 2016. The significance of the sleep survey was explained to the guardian, and they were invited to participate voluntarily. The data of sleep wake state was obtained using a sleep log form in which cells representing every 30 minutes in 24 hours were filled out to record sleep time continuously for two weeks. The sleep log forms were handed to the guardians before starting the sleep measurement and they were asked to fill the form to record the sleep wake state of their children at home for two weeks. The sleep wake state of the children at nurseries were recorded by the staff and the record was transcribed to their sleep log forms after the sleep measurement period.”

(The manuscript was edited by MDPI Author Services.)

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

I think the article focuses on an interesting topic: the ontogeny of sleep, particularly of Japanese kids in modern society.

I have attached my comments, which will be addressed in rewriting process.

General comments:

In the results and Figure 3 there is taken into account only night-time duration of sleep and phase delaying of sleep. However, according to recommendations of the American Academy of Sleep Medicine (Paruthi et al., 2016), the data about total sleep (with daytime naps included along with the nighttime sleep duration) for children are substantial especially in early childhood when the daytime naps are present. Thereafter the nighttime sleep duration would not be the only factor for assessing sleep sufficiency during infancy.

I am not expert in field of the children sleep so I have a question why did you choose just a night-time sleep for assessing the sufficiency of the sleep in your study?

In my opinion, you have to add a figure with the total duration of sleep and discuss more the total sleep in the article.

I lack the information about number of naps during the day in all age groups. How does the number of naps change with age? It would be practical information for parents and / or caregivers of children.

In line with the previous comment, according to the article title I did not find sleep hygiene guidance in the article. Please, change the article title.

Introduction:

L48-50: Due to changes in lifestyle and excessive use of artificial lighting and/or personal devices it is known that sleep time onset in industrial societies is delayed. Is there some exact data about sleeping in Japan, especially children´s sleep in the 1960s, or other years (1970s or 1980s) before the excessive usage of electrical personal devices such as PC, tablets, etc. not only in the Japanese language? If yes, please add the reference.

Thereafter, you mention only the onset of the sleep in 1960s, but what was the waking up time in the 1960s, and consequently, night-time sleep duration? Do you have some exact information about night-time sleep and/or daytime naps duration shortening especially in kids up to 6 years?

Methods:

L494-506 Defining night sleep-onset time is not clear, please correct it.

Particularly, what does the point 2 refer to? If I understand well, point 1 refers to starting sleep at 24:30 or later.

L531-532 Due to cultural differences and for better clarity I suggest adding the definition of nighttime weekend sleep. The onset of weekend sleep started on Fridays or Saturday evenings? Tthe onset of weekday sleep starts on Sunday evenings?.

In the results there is the “Trend test” mentioned. Trend test was made within ANOVA or it was an independent test? Please clarify it in Methods, in “statistical analysis”.

Results:

Detailing the results in the text in lines L85-92, L108-114, L168-187 is a repeated/doubled presentation of the results, which are also shown in tables and graphs L85-92 (Table 1, Figure1), L108-114 (Table 1, Figure1), L168-176, 179-186 (Table 2, Figure 2). I recommend remove it from text and leave there just a description of the statistics.

10a: L101-103: there are mentioned significances between “sleep-onset time of weekdays 0 y old group and OTHER age groups”. It is not clear if “other” means “all other” groups or only these ones marked in Figure 1. If “other” means “all” groups, it is necessary to add significancies in Figure 1.

10b. In a similar way, please clarify L122-128.

11a: L105-107: please clarify the sentence: L 105-107 “The results also show a TENDENCY of significant difference in the night sleep-onset time between the 2-year-old group and three-year-old group (p<0.05)”. Particularly to what the word “tendency refers “(Tendency was done with trend test?). If needed add this (p<0.05) in Figure 1.

11b. Similarly, please clarify the sentence in L128-129. If needed add this (p<0.05) in Figure 1.

Lines 134-136: Please clarify the sentence: The difference in the average sleep-onset time between weekends and weekdays of each subject was calculated and the difference in sleep-onset time between ADJACENT age groups was confirmed” particularly what does it mean “adjacent” in this sentence?

In figure 1 there is “**p<0.01”, but in the graph there are no differences at this p-level. Please, remove it.

In the text there are significantly shorter daytime sleep duration at weekends than on weekdays. These differences are not marked in Figure 2. Please, add it to Figure 2.

L245-246 sleep deprivation group delayed all sleep phase or only waking time on weekends? So, if the sleep-deprived children came to the sleep-delayed group they have sufficient sleep during weekends?

Discussion:

L279-281 It is questionable if “the circadian rhythm formation s completed in 1,5 years”. The references are not appropriate for this statement.

The total sleep is little discussed and I lack the more information about total sleep length (see the comment 1).

Author Response

Response to Reviewer 3 Comments

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.　 I am not a native English speaker, so there may be some problems with the details of my expressions. I try to be careful not to use rude expressions, but there may be some problems due to the reasons mentioned above. I hope you will forgive me in that case.

Point-by-point response to Comments and Suggestions for Authors

Comment 1:

In the results and Figure 3 there is taken into account only night-time duration of sleep and phase delaying of sleep. However, according to recommendations of the American Academy of Sleep Medicine (Paruthi et al., 2016), the data about total sleep (with daytime naps included along with the nighttime sleep duration) for children are substantial especially in early childhood when the daytime naps are present. Thereafter the nighttime sleep duration would not be the only factor for assessing sleep sufficiency during infancy.

Response 1:

Thank you for your question. First, thank you for introducing the paper by Paruthi S et al. We are aware of this paper and use it as a guide for the appropriate total sleep time for children. I would like to add this paper to the references. What is a bit disappointing is that this paper also focuses on the appropriate total sleep time for each generation, and does not mention chronobiological issues such as the background of naps, daily school and social life. However, I think the important thing is that the authors encourage people to sleep " on a regular basis to promote optimal health ". If we evaluate the quantity and quality of sleep by the total duration of sleep per day, we will accept a dual rhythm of compensating for lack of sleep at night with daytime naps, which may lead to circadian rhythm disruption.

When considering a child's daily rhythm, it is necessary to consider the daily time period, including the total sleep time and nap time, as a circadian rhythm. We believe this is exactly what Parti et al. mean when they say " on a regular basis to promote optimal health."

Comments 2:

I have a question why did you choose just a night-time sleep for assessing the sufficiency of the sleep in your study?

Response 2:

We are not intending just talking about nighttime sleep, but that nighttime sleep is a pillar of the circadian rhythm that underpins daily life, especially in children. Naturally, lack of sleep at night leads to longer and/or irregular naps to compensate, and oversleeping on holiday mornings (finally social jet lag), which can lead to mental and physical discomfort and future difficulties in school and social life, if we cannot take nap time in school. We believe that regular, sufficient nighttime sleep helps establish circadian rhythms that promote optimal health. We don't just talk about "nighttime sleep" when talking about adult sleep, but we think "nighttime sleep" is just as important when talking about children's sleep. The importance of naps may apply to children who don't get enough sleep at night, but we don't think naps that are too long, compensating loss of night time sleep, are very healthy. Therefore, we think it is important to clearly communicate to children and parents that nighttime sleep is a pillar. When nighttime sleep is ensured regularly and clearly, naps will appear regularly as part of the circadian rhythm of life. This leads to appropriate nap times and frequency, and it is desirable for them to occur regularly.

Comments 3:

In my opinion, you have to add a figure with the total duration of sleep and discuss more the total sleep in the article.

Response 3：

The duration of sleep required per day is considered to be the sum of the nighttime basic sleep duration (NBSD) and the time spent napping. The total amount of sleep per day has been added to the discussion as a comparison with previous literature data (line 206-212).

Comments ４:

I lack the information about number of naps during the day in all age groups. How does the number of naps change with age? It would be practical information for parents and / or caregivers of children.

Response 4:

Your suggestion is an interesting one for me to consider for my next research. I would like to have the opportunity to report on the difference in the number and duration of naps between the group with a regular lifestyle and the group with an irregular lifestyle at the next opportunity. Please allow me to state the number of naps based on the　already reported papers (line 281-286: 22,32). Many of the papers on children's sleep reported so far have been written in a tone that it is enough if the total amount of sleep per day is secured, and I am concerned that a common sense has been created that insufficient nighttime sleep can be made up for by naps. I have thought that this way of thinking does not necessarily support children's lives correctly. From the research that the authors have conducted so far, the question has arisen as to whether the issue of how to secure the amount of nighttime sleep by the time of waking up is more important. In other words, it is a problem of life rhythm in school society. Therefore, this time I have avoided including too much information and reported on the importance of securing nighttime sleep and the issue of how to secure that continuous sleep by the fixed time of waking up in the morning. I believe that the formation of this regular life rhythm will lead to regular and appropriate number of naps and will regulate the daily life rhythm.

Ma, G.; Segawa, M.; Nomura, Y.; Kondo, Y.; Tanagitani, M.; Higurashi, M. The Development of Sleep-Wakefulness Rhythm in Normal Infants and Young Children. Tohoku J. Exp. Med. 1993, 171, 29-41.
Weissbluth, M. Naps in Children: 6 months-7 Years Sleep. 1995 Feb;18(2):82-87. [CrossRef] [PubMed]

Comment 5:

In line with the previous comment, according to the article title I did not find sleep hygiene guidance in the article. Please, change the article title.

Response 5:

According to your suggestion, we change the title below.

“Characteristics and transition of sleep-wake rhythm during nursery school children: The importance of nocturnal sleep”

Comment 6: Introduction:

L48-50: Due to changes in lifestyle and excessive use of artificial lighting and/or personal devices it is known that sleep time onset in industrial societies is delayed. Is there some exact data about sleeping in Japan, especially children´s sleep in the 1960s, or other years (1970s or 1980s) before the excessive usage of electrical personal devices such as PC, tablets, etc. not only in the Japanese language? If yes, please add the reference.

Response 6:

There are one or two comparative studies on adolescents, but I could not find any studies on infancy.

Comment 7

Thereafter, you mention only the onset of the sleep in 1960s, but what was the waking up time in the 1960s, and consequently, night-time sleep duration? Do you have some exact information about night-time sleep and/or daytime naps duration shortening especially in kids up to 6 years?

Response 7:

As you point out, this is important information, but the data from 1960 is fragmented and not detailed.　(line 62-68) Comparing the percentage of children who go to bed after 10pm in 1980, 1990 and 2000, there has been a marked increase: 25% → 38% → 55% for 18-month-olds, 29% → 41% → 59% for 2-year-olds, 22% → 36% → 52% for 3-year-olds, 13% → 23% → 39% for 4-year-olds, and 10% → 17% → 40% for 5-6-year-olds, showing that children's lifestyle rhythms are becoming more nocturnal each year.　Wake-up times on weekdays remain roughly between 6:50 and 7:00, with no major change.

9.Ishihara, K.; Doi, Y.; Uchiyama, M. Sleep and health from early childhood to preadolescence. J. Natl. Inst. Public Health, 2015, 64(1), 3-10.（in Japanese with English abstract）

Comment 8:

L494-506 Defining night sleep-onset time is not clear, please correct it.

Response 8:

I hope it has been improved and made easier to understand.(line 397-408)

The night bedtime was defined as a time after 18:00 when the child was sleeping continuously for 1.5 hours or more. However, if the bedtime was after 24:30 or later, the earlier of the two shown below was recorded as the night bedtime.

After 18:00 if children sleep for 0.5 hours, wake up for 0.5 hours or more, and then

sleep for 0.5 hours or more after that, the time children first fall asleep is considered bedtime.

A time when the children fell asleep after 18:00 and slept for at least one continuous hour.

If the children slept only for 30 minutes between 19:00 and 7:00 the following morning, the time when the children fell asleep was considered to be the night bedtime. If the time when the children fell asleep was later than midnight, 24 was added to the time. For example, if the time was 1:30 it was considered to be 25:30.

Comment 9:

Particularly, what does the point 2 refer to? If I understand well, point 1 refers to starting sleep at 24:30 or later.

Response 9:

I think that interpretation is fine.

Comment 10:

L531-532 Due to cultural differences and for better clarity I suggest adding the definition of nighttime weekend sleep. The onset of weekend sleep started on Fridays or Saturday evenings?

Response 10: (line 439-441)

Weekday sleep was defined as sleep from midnight (0 o'clock) on Monday to midnight (24 o'clock) on Friday, and weekend sleep was defined as sleep from midnight (0 o'clock) on Saturday to midnight (24 o'clock) on Sunday.

Comment 11:

In the results there is the “Trend test” mentioned. Trend test was made within ANOVA or it was an independent test? Please clarify it in Methods, in “statistical analysis”.

Response 11:

“The trend relationship of 0 year to 6 years of age with bedtime, waketime, sleep duration were tested by Jonckheere-Terpstra trend test.”

Is added in methods.(line 445-446)

Comment 12: Results:

Detailing the results in the text in lines L85-92, L108-114, L168-187 is a repeated/doubled presentation of the results, which are also shown in tables and graphs L85-92 (Table 1, Figure1), L108-114 (Table 1, Figure1), L168-176, 179-186 (Table 2, Figure 2). I recommend remove it from text and leave there just a description of the statistics.

Response 12:

We remove it from text and leave there just a description of the statistics.

Comment 1３:

10a: L101-103: there are mentioned significances between “sleep-onset time of weekdays 0 y old group and OTHER age groups”. It is not clear if “other” means “all other” groups or only these ones marked in Figure 1. If “other” means “all” groups, it is necessary to add significancies in Figure 1.

10b. In a similar way, please clarify L122-128.

Response 13:

I think creating a box plot solved it.

Comment 14:

Lines 134-136: Please clarify the sentence: The difference in the average sleep-onset time between weekends and weekdays of each subject was calculated and the difference in sleep-onset time between ADJACENT age groups was confirmed” particularly what does it mean “adjacent” in this sentence?

Response 14:

We deleted the word “Tebdency”.

Comment 15:

In figure 1 there is “**p<0.01”, but in the graph there are no differences at this p-level. Please, remove it.

In the text there are significantly shorter daytime sleep duration at weekends than on weekdays. These differences are not marked in Figure 2. Please, add it to Figure 2.

Response 15:

Both resolved by creating new Figures.?

Comment 16: Discussion:

L279-281 It is questionable if “the circadian rhythm formation s completed in 1,5 years”. The references are not appropriate for this statement.

Response 16:

I have rephrased it as circadian rhythm of sleep wake.

Reviewer 4 Report

Comments and Suggestions for Authors

This paper is based on a two-week observations of sleeping habits of (very) young citizens of Tokio, attending nursery institutions. It involved a large sample (over 4800 participants or the same number of their guardians) and provides robust data on the bedtimes and wake-up times of children on both weekdays and weekends. The most important conclusion of the study points to the necessity of recognizing the NBSD of children and postulates maintaining the same waking time on weekdays and weekends. To be honest, the conclusions go a bit further than the results of the study allow, but they are supported by knowledge from the relevant literature.

I particularly appreciated the Discussion section of the paper (especially intercultural comparisons). In my opinion it is worth sharing with readers worldwide :)

Remarks:

Abstract, line 26

sleep dept ? à sleep debt

Page 2, line 52

“Modern nocturnal lifestyle is widespread all over the world, involves children and forces them to sleep late/get up early to deteriorate their sleeping environment.”

Maybe it would be better like this: “A modern nocturnal lifestyle is widespread globally, affecting children and forcing them to sleep late and wake up early, which deteriorates their sleep environment.”

Page 2, lines 85-92

Page 3, lines 108-114

I was wondering if it might be better to present this in tables? Then I discovered it is indeed in Table 1 – but isn’t it redundant?

Page 5, Figure 1 – description (lines 151-157) redundant – it is easy to understand the figure after seeing the legend. Last three lines (158-162) should be included in the main text.

Pages 6-7, lines 168-192 – the same problem as above – information doubled – the same is in the text and in the table – and it makes no sense.

Page 7-8, lines 209-214

This comment should be moved from the figure’s description to the main text.

Page 9, line 277-278

“In this study, sleep onset time and wake up time gradually shifted after birth, becoming just over 30 and 20 minutes more later by age 2, respectively.” more later --> later

Page 13, lines 447-448

“Through this study, we would like to emphasize that the establishment of a daily rhythm centered on the time of daily life is an important factor for the mental and physical growth of children.”

Perhaps: “Through this study, we would like to highlight/emphasize that establishing a daily rhythm centered around consistent daily routines is a crucial factor for the mental and physical development of children.”

Author Response

Comments 1:

Abstract, line 26

sleep dept ? à sleep debt

Response 1:

Sleep debt. Is correct.

Comments 2:

Page 2, line 52

“Modern nocturnal lifestyle is widespread all over the world, involves children and forces them to sleep late/get up early to deteriorate their sleeping environment.”

Response 2:

Thank you very much. The sentence you advised me on is clear and concise.(line 69-71)

“A modern nocturnal lifestyle is widespread globally, affecting children and forcing them to sleep late and wake up early, which deteriorates their sleep environment.”

Comments 3:

Page 2, lines 85-92

Page 3, lines 108-114

I was wondering if it might be better to present this in tables? Then I discovered it is indeed in Table 1 – but isn’t it redundant?

Response 3:

I changed the chart to a "box plot" so that it could be shown in the figure.

Comments ４:

Page 5, Figure 1 – description (lines 151-157) redundant – it is easy to understand the figure after seeing the legend. Last three lines (158-162) should be included in the main text.

Response ４:

We deleted the following sentences.

The pairs of lines on the lower side represent the morning wake time of each age group where the left line of each pair represents the wake time on weekdays and the right line of each pair represents the wake time on weekends. The pairs of lines on the upper side represent the night sleep-onset time of each age group where the left line of each pair represents the sleep-onset time on weekdays and the right line of each pair represents the sleep-onset time on weekends. The time scale for the sleep-onset time is given on the left of the ordinate and that for the wake time is given on the right of the ordinate.

Comments ５:

Last three lines (158-162) should be included in the main text.

Response ５:

We agree with your point. This is shown in Figure 1-2.(Box plot)

Comments 6:

Pages 6-7, lines 168-192 – the same problem as above – information doubled – the same is in the text and in the table – and it makes no sense.

Response 6:

We agree with your point, so we decided to remove the table and show it as a box plot (Fig1-2).

Comments 7:

Page 7-8, lines 209-214

This comment should be moved from the figure’s description to the main text.

Response 7:

We agree with your point, so we decided to remove the table and show it as a box plot (Fig2).

Comments 8:

Page 9, line 277-278

“In this study, sleep onset time and wake up time gradually shifted after birth, becoming just over 30 and 20 minutes more later by age 2, respectively.” more later --> later

Response ８:

Changed "more later" to "later".　Thank you.

Comments ９:

Page 13, lines 447-448

“Through this study, we would like to emphasize that the establishment of a daily rhythm centered on the time of daily life is an important factor for the mental and physical growth of children.”

Response ９

This expression is exactly what we want to assert. Therefore, we have inserted it in the conclusion. Thank you very much for your advice.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for accepting my comments in new version of your article.

I have some reminds particularly to graphs and the description of statistics in them.

Graphs:

Figures 1 and 2: It is necessary to add description of box plot characteristics (not only x- mean, quartiles, what type of error bars).

Figures 1 and 2: I am confused about p-values in graphs: * usually means p<0.05, you have in your graph *p<0.01 (p<0.01 is usually **). But in original version of your article there are p-levels in the graphs with the same results signed as *** (p<0.001). Also, in original article the “cross symbol” means p<0.001 not p<0.01 as in revised version.

I don´t know if you changed the statistics or you have mistaken in your new version. Revise Figures 1 and 2 in term of proper p-values and their designation.

Graphs in Fig. 2, particularly, daytime sleep hours during weekdays cannot be in a present form. Box plots and error bars should be visible even if they are in negative numbers. Please, revise it.

Text:

1. Line 415: In revised version I can see 12:30 a.m. The time in this form is not properly expressed. Use 00:30 or 24:30. In scientific paper is better to use time from 00:00 - 24:00 as you use in all paper.

2. In your answer to comment 8 I cannot see the clarifying of the sentence, but in revised version I can see:

415 earlier of the two times listed below was recorded as the night bedtime:

The words “earlier of the two times listed below” clarify my comment 8. So, it is fine in this form.

Author Response

Dear reviewer

Once again, thank you for your appropriate comments. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. Thank you for taking the time to review this article.

Point-by-point response to Comments and Suggestions for Authors

Comment 1：

Graphs:

Figures 1 and 2: It is necessary to add description of box plot characteristics (not only x- mean, quartiles, what type of error bars).

Response　１: We have added a description of the characteristics of the box plot, in line with the reviewer's suggestion.

Comment ２：

I don´t know if you changed the statistics or you have mistaken in your new version. Revise Figures 1 and 2 in term of proper p-values and their designation.

Response　２: Thank you for pointing out this issue. We have carefully reviewed the analysis results and corrected the Figures.

Comment ３：

Graphs in Fig. 2, particularly, daytime sleep hours during weekdays cannot be in a present form. Box plots and error bars should be visible even if they are in negative numbers. Please, revise it.

Response３: In the box plot, the bottom and top edges of the boxes represent the 25th and 75th percentile of the data, respectively. The lines in the boxes represent the median of the data. The lower and upper ends of the error bars represent the minimum and maximum values, excluding outliers, respectively. The minimum value for daytime sleep duration is 0; therefore, in the box plots in Fig. 2, the box and the error bar are never negative number.

Comment ４：

Text:

Line 415: In revised version I can see 12:30 a.m. The time in this form is not properly expressed. Use 00:30 or 24:30. In scientific paper is better to use time from 00:00 - 24:00 as you use in all paper.

Response４:

In the revised version, 12:30 am has been changed to 00:30. (Line 418)

Comment 5：

In your answer to comment 8 I cannot see the clarifying of the sentence, but in revised version I can see:

415 earlier of the two times listed below was recorded as the night bedtime:

The words “earlier of the two times listed below” clarify my comment 8. So, it is fine in this form.

Response 5:

I understood. Thank you.