Are the Sleep–Wake Cycle and Sleep Duration Ethnically Determined? A Comparison of Tibetan and Japanese Children’s Sleep

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is very interesting and relevant to pediatric sleep medicine. However I found a few major and minor flaws:

1. Authors have to improve the study reporting. Authors have to use the STROBE Statement. Please use the STROBE checklist for your type of observational study.

2. Authors have to clarify the aim of the study at the end of Introduction.

3. Authors have to describe in details the process of the survey distribution and administration.

4. Authors have to provide detail inclusion and exclusion criteria for study participants.

5. Authors cited a lot of very old literature (older than 10 years). The sleep medicine field is changing very fast and Authors should mainly to present the latest literature. Therefore I strongly recommend to present in Introduction or Discussion three very important and latest articles related to pediatric sleep medicine:

doi: 10.1016/j.sleepx.2021.100035 The study showed that Prevalence of possible SB was 35% and screen-time was available for 92.9% of the children. Mean screen-time was 2.1 h/day. Parents reported 73% of the children (n = 319) to consume added sugar once a day every day and 20% more than once every day. Correlations of possible SB were statistically significant with screen-time (Rho = 0.8; p = 0.002) and sugar-consumption (Rho = 0.7; p = 0.03). Associations were found between possible SB and increase-to-increase screen-time and sugar-consumption (OR > 2).

doi:10.17219/dmp/150615 The study showed that among sleeping habits, bedtime resistance was found to be significantly associated with sleep bruxism and temporomandibular disorders (TMD) symptoms in children. Sleep behavior problems were also found to be related to TMD. Untreated dental caries was significantly associated with sleep fragmentation.

doi:10.17219/dmp/167411 The study showed that the group with inappropriate sleep patterns had significantly lower pH and buffering capacity (p < 0.001) and significantly higher colony counts of Lactobacillus and S. mutans (p < 0.001 and p = 0.012, respectively). There was no association between C. albicans and sleep patterns (p = 0.121).

The above mentioned studies showed that sufficient sleep in children is very important for general health, oral health and development of pediatric population.

6. Authors have to provide a legend of used abbreviations below each table.

Author Response

1. Responses to Reviewer 1

   1. Authors have to improve the study reporting. Authors have to use the STROBE Statement. Please use the STROBE checklist for your type of observational study.

    

   Thank you for your valuable comments. We used STROBE and changed/added the following words:

    

   Abstract

   We conducted a community-based cross-sectional study using the Chinese version of the Japanese Sleep Questionnaire for Preschoolers (JSQ-P-C) and compared the results with previous data on Japanese children. (line 12-14)

    

   4.1. Participants

   Exclusion criteria were the cases where consent could not be obtained and the cases with a medical diagnosis of sleep disorders. (line 218-220)

    

   Institutional Review Board Statement:

   The study protocol and questionnaires were approved by the Human Research Ethics Committee of the Institutional Review Board of Osaka University Hospital (#19007) on June 24th, 2019. (line 271-273)

    

   2. Authors have to clarify the aim of the study at the end of Introduction.

   Thank you for your valuable comments. We have added a sentence at the end of the Introduction section.

    

   Using demographic data from the JSQ-P and JSQ-P-C, we compared the sleep and sleep-related habits of preschoolers in Tibet and Japan to determine whether sleep changes with the environment. (line 79-81)

    

   3. Authors have to describe in details the process of the survey distribution and administration.

   Thank you for your comments. Details of the process are given in Section 4.1. Participants. The text has been moved to the Measurement section and is described in more detail.

    

   4.1. Participants

   The survey was administered in kindergartens, where the principals agreed to distribute the questionnaires in the classroom. Questionnaires, such as JSQ-P-C and socioeconomic status, were distributed after explanation by the researchers (PS and IM). The caregivers of the children were informed that participation was free of charge; they were asked to complete the questionnaire anonymously and return it two days later. Submission of the questionnaire was considered consent for participation. Exclusion criteria were the cases where consent could not be obtained and the cases with a medical diagnosis of sleep disorders. (line 213-220)

    

   4. Authors have to provide detail inclusion and exclusion criteria for study participants.

   As you pointed out, we did not provide inclusion criteria for study participants. We have added the following inclusion criteria for participants:

    

   4.1. Participants

   Exclusion criteria were the cases where consent could not be obtained and the cases with a medical diagnosis of sleep disorders. (line 218-220)

    

   5. Authors cited a lot of very old literature (older than 10 years). The sleep medicine field is changing very fast and Authors should mainly to present the latest literature. Therefore I strongly recommend to present in Introduction or Discussion three very important and latest articles related to pediatric sleep medicine:

   doi: 10.1016/j.sleepx.2021.100035 The study showed that Prevalence of possible SB was 35% and screen-time was available for 92.9% of the children. Mean screen-time was 2.1 h/day. Parents reported 73% of the children (n = 319) to consume added sugar once a day every day and 20% more than once every day. Correlations of possible SB were statistically significant with screen-time (Rho = 0.8; p = 0.002) and sugar-consumption (Rho = 0.7; p = 0.03). Associations were found between possible SB and increase-to-increase screen-time and sugar-consumption (OR > 2).

   doi:10.17219/dmp/150615 The study showed that among sleeping habits, bedtime resistance was found to be significantly associated with sleep bruxism and temporomandibular disorders (TMD) symptoms in children. Sleep behavior problems were also found to be related to TMD. Untreated dental caries was significantly associated with sleep fragmentation.

   doi:10.17219/dmp/167411 The study showed that the group with inappropriate sleep patterns had significantly lower pH and buffering capacity (p < 0.001) and significantly higher colony counts of Lactobacillus and S. mutans (p < 0.001 and p = 0.012, respectively). There was no association between C. albicans and sleep patterns (p = 0.121).

   The above mentioned studies showed that sufficient sleep in children is very important for general health, oral health and development of pediatric population.

    

   Thank you for your valuable comments. We did not adopt this perspective. Sleep bruxism, temporomandibular disorders (TMD) symptoms are very important factor for children’s sleep, and oral health also big issue. However, mentioning these may not make the theme of this paper clear. These points will be analyzed further and reported in a forthcoming paper.

    

   Authors have to provide a legend of used abbreviations below each table.

    

   Thank you for pointing this out. We are sorry, but the test method for Table 1 was incorrect. When we double-checked, we used the Kruskal-Wallis test rather than Fisher's least significant difference test　because the data were non-normally distributed. We have corrected the text and added legends for the abbreviations below each table as follows:

    

   4.3. Statistical Analysis

   The Kruskal-Wallis test compared the sleep habits of three age groups of children in Qinghai: 3 years old, 4 years old and >5 years old. (line 248-249)

    

   Table 1

   Median and interquartile range of sleep-related habits of children in Qinghai province. Kruskal-Wallis test. (line 122)

    

   Table 2

   Means and SD of sleep time and sleep-related habits of children in Qinghai province and Japan. Mann–Whitney U test. (line 138)

   Table 3

   Geographic data on altitude, time of sunrise and sunset, and the population of each district. (line 229)

Reviewer 2 Report

Comments and Suggestions for Authors

Review; Is sleep-wake cycle and sleep duration genetically determined? Comparison of Tibetan and Japanese children's Sleep.

Summary.              

The authors try to determine underlying reasons for different sleep and wake times in two different community samples.

Major

-          The title is misleading. It seems to suggest that the authors are looking at genetic factors contributing to sleep-wake differences when in reality, you are looking at habits. This can have a genetic component but also cultural/environmental causes

-          The overall relevance is hard to determine. According to the authors, a lot is already known about sleep and sleep habits in these populations, so what was the goal of this study? This makes it hard to assess the relevance of the presented manuscript.

 

Results

-          “The background data, such as age, educational level of the caregivers, and monthly family income of the four regions, were previously reported. “ à please add a reference. Also briefly outline the populations, as this is essential background information

 

Discussion

-          It would be nice if the authors could first provide a brief summary of the study and study goal before delving into a discussion of the results.

Limitations.

-          I think another limitation is that all data is based on self-report, and no objective measurements were used. There is always some bias in self-report, and this has to be acknowledged.

Materials & Methods

-          As the sample is unbalanced (n=312 Tibetan children, n=2,553 Japanese), is Fisher’s test robust enough to handle this imbalance?

-          It’s unclear how the authors assessed statistical differences among the three groups. If something is statistically significant, does that imply differences between all three groups, or just between two? If it’s the latter, which two groups? Also, did the authors conduct any post-hoc testing?

-          The authors state that they used Cohen’s D, but in the text, they report Eta squared, which is a different metric of effect size.

Conclusion

 

-          The authors cannot state that it is “probably due to genetic factors” as there are other confounding factors that could have contributed to these differences. Moreover, the authors did not actually measure genetic polymorphisms, so this is highly speculative. 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Although the sentence structure is strong, the overall organization of the manuscript could benefit from some restructuring to improve its logical flow

Author Response

Responses to Reviewer 2

 

Major

-          The title is misleading. It seems to suggest that the authors are looking at genetic factors contributing to sleep-wake differences when in reality, you are looking at habits. This can have a genetic component but also cultural/environmental causes

 

Thank you for your comments. We have revised the title of our manuscript as follows:

 

Title

Is sleep-wake cycle and sleep duration ethnically determined? Comparison of Tibetan and Japanese children's Sleep.

 

Discussion

We deleted the sentence “These findings may suggest that late bedtime in Asian children may be genetically regulated.”

 

Considering that Tibetan children also show late bedtime patterns despite not having busy schedules, like Japanese children, there might be a genetic relationship with bedtime. (line 187-189)

 

-          The overall relevance is hard to determine. According to the authors, a lot is already known about sleep and sleep habits in these populations, so what was the goal of this study? This makes it hard to assess the relevance of the presented manuscript.

 

Thank you for your comments. Environmental factors strongly influence sleep. In Japan, media use is becoming increasingly younger, with television programs available 24 h a day. To investigate whether children's short sleep duration in Japan is affected by these environments, a comparison was made with children in Tibet, where TV programs and video games are less common than in Japan. As sleep circumstances also have a significant impact on sleep, we hypothesized that a comparison with Tibet, where co-sleeping is the norm during childhood, would be meaningful.

We added some sentences to clarify the purpose of this paper.

 

Introduction

 Qinghai Province is located in the eastern hinterland of the Qinghai-Tibet Plateau in western China at 2,000 meters above sea level (masl). The main industries in Qinghai are sheep and yak farming. In 2016, Qianhai’s gross domestic product was $378.45 billion (7.6% of Japan’s), and per capital income was $6.400 (16% of Japan’s). Electric appliances, such as mobile phones and video games, are less common among children in Qinghai than in Japan. Television (TV) programs for children are much less popular, with only one program, “QRTV-5,” compared to Japan, where TV programs are available 24 h a day. As Tibet and Japan have the same sleeping habits of co-sleeping but very different environments in terms of media use, it was considered useful to study children's sleep in both countries.

Using demographic data from the JSQ-P and JSQ-P-C, we compared the sleep and sleep-related habits of preschoolers in Tibet and Japan to determine whether sleep changes with the environment. (line 69-81)

 

Results

-          “The background data, such as age, educational level of the caregivers, and monthly family income of the four regions, were previously reported. “ à please add a reference. Also briefly outline the populations, as this is essential background information.

 

We apologize; however, the previous report was just accepted in High Altitude medicine & Biology.

We have added background information to the Results section and cited that article.

 

The mean age of the participants was 4.9 ± 0.4 years and 50.9% were boys. The ages of the father and mother were 34.6 ± 6.1 and 32.3 ± 5.7 years, respectively. Regarding the educational level of caregivers, the ratio of junior high school and lower was 49.0% of the fathers and 49.3% of the mothers. Family income below CNY 4,000 is 46.4% [23]. (line 92-95)

 

Discussion

-          It would be nice if the authors could first provide a brief summary of the study and study goal before delving into a discussion of the results.

 

Thank you for your suggestion. We have added the following sentence to provide a brief summary of the study and its goals.

 

Discussion

This study examined the sleep of children in Tibet, a region where TV and video games are less common, and compared the sleep of children in two regions, Tibet and Japan, which have similar sleep habits but very different environments, to investigate the effects of the environment on sleep. (line 141-144)

 

Limitations.

-          I think another limitation is that all data is based on self-report, and no objective measurements were used. There is always some bias in self-report, and this has to be acknowledged.

 

Thank you for pointing this out. This is a very important point. We added a sentence in the Limitations section as the following.

 

There could have been parental and retrospective bias in the responses to the items because parents completed the questionnaires based on recollection. (line 202-204)

 

 

Materials & Methods

-          As the sample is unbalanced (n=312 Tibetan children, n=2,553 Japanese), is Fisher’s test robust enough to handle this imbalance?

 

It is our mistake. The statistical method used for Table 1 was Kruskal-Wallis test and Table 2 was the Mann–Whitney U test. We rewrite the section of Statistical Analysis and added a legend to each table to clarify the statistical methods used.

 

4.3. Statistical Analysis

The Kruskal-Wallis test compared the sleep habits of three age groups of children in Qinghai: 3 years old, 4 years old and >5 years old. (line 248-249)

 

Table 1

Median and interquartile range of sleep-related habits of children in Qinghai province. Kruskal-Wallis test. (line 122)

 

Table 2

Means and SD of sleep time and sleep-related habits of children in Qinghai province and Japan. Mann–Whitney U test. (line 138)

 

-          It’s unclear how the authors assessed statistical differences among the three groups. If something is statistically significant, does that imply differences between all three groups, or just between two? If it’s the latter, which two groups? Also, did the authors conduct any post-hoc testing?

 

Thank you for your critical reading.

Significant differences were observed among the three groups. We have added additional words to clarify this.

 

No significant differences were observed between the three groups. (line 103-104)

 

We did not conduct any post-hoc testing. The median value is not big different. We think the significant due to the large number of people.

 

 

-          The authors state that they used Cohen’s D, but in the text, they report Eta squared, which is a different metric of effect size.

 

We are sorry, it is our mistake. The statistical method used for Table 1 was Kruskal-Wallis test and Table 2 was the Mann–Whitney U test. We corrected the table and manuscript.

 

4.3. Statistical Analysis

The Kruskal-Wallis test compared the sleep habits of three age groups of children in Qinghai: 3 years old, 4 years old and >5 years old. For international comparison, we used data from Tibetan children (n=312) and Japanese children (n = 2,553) at the age of 3 years as previously reported [11], using Mann–Whitney U test. Effect sizes (Cohen’s d) were calculated for the variables with significant differences. (line 248-252)

 

Table 1

Median and interquartile range of sleep-related habits of children in Qinghai province. Kruskal-Wallis test. (line 122)

 

Table 2

Means and SD of sleep time and sleep-related habits of children in Qinghai province and Japan. Mann–Whitney U test. (line 138)

 

Conclusion

 

-          The authors cannot state that it is “probably due to genetic factors” as there are other confounding factors that could have contributed to these differences. Moreover, the authors did not actually measure genetic polymorphisms, so this is highly speculative. 

 

Thank you for your comments. As you have mentioned, we did not examine these genes. We have revised the title and other words in the Discussion section.

 

Title

Is sleep-wake cycle and sleep duration ethnically determined? Comparison of Tibetan and Japanese children's Sleep.

 

Discussion

We deleted the sentence “These findings may suggest that late bedtime in Asian children may be genetically regulated.”

 

Considering that Tibetan children also show late bedtime patterns despite not having busy schedules, like Japanese children, there might be a genetic relationship with bedtime. (line 187-189)

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been correctly revised. I don't have further comments.

Author Response

Responses to Reviewer 1

5. Authors cited a lot of very old literature (older than 10 years). The sleep medicine field is changing very fast and Authors should mainly to present the latest literature. Therefore I strongly recommend to present in Introduction or Discussion three very important and latest articles related to pediatric sleep medicine:

doi: 10.1016/j.sleepx.2021.100035 The study showed that Prevalence of possible SB was 35% and screen-time was available for 92.9% of the children. Mean screen-time was 2.1 h/day. Parents reported 73% of the children (n = 319) to consume added sugar once a day every day and 20% more than once every day. Correlations of possible SB were statistically significant with screen-time (Rho = 0.8; p = 0.002) and sugar-consumption (Rho = 0.7; p = 0.03). Associations were found between possible SB and increase-to-increase screen-time and sugar-consumption (OR > 2).

doi:10.17219/dmp/150615 The study showed that among sleeping habits, bedtime resistance was found to be significantly associated with sleep bruxism and temporomandibular disorders (TMD) symptoms in children. Sleep behavior problems were also found to be related to TMD. Untreated dental caries was significantly associated with sleep fragmentation.

doi:10.17219/dmp/167411 The study showed that the group with inappropriate sleep patterns had significantly lower pH and buffering capacity (p < 0.001) and significantly higher colony counts of Lactobacillus and S. mutans (p < 0.001 and p = 0.012, respectively). There was no association between C. albicans and sleep patterns (p = 0.121).

The above mentioned studies showed that sufficient sleep in children is very important for general health, oral health and development of pediatric population.

Thank you for your valuable comments. We did not adopt this perspective. Sleep bruxism, temporomandibular disorders (TMD) symptoms are very important factor for children’s sleep, and oral health also big issue. However, mentioning these may not make the theme of this paper clear. These points will be analyzed further and reported in a forthcoming paper.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I thank the authors for addressing my comments and concerns. 

I have one concern left concerning the title. While I appreciate that "genetic" has been removed,  I am not sure if "ethnically" is the right term to replace it with. Probably "culturally" would be more appropriate.

Comments on the Quality of English Language

The introduction misses some focus; it talks a lot about the importance of sleep (two paragraphs), but that is not what the article is about - as no health outcomes ar being tested. 

Author Response

Responses to Reviewer 2  second round

I thank the authors for addressing my comments and concerns. 

I have one concern left concerning the title. While I appreciate that "genetic" has been removed,  I am not sure if "ethnically" is the right term to replace it with. Probably "culturally" would be more appropriate.

Thank you for your nice suggestion. It seems better for us.

We changed  the title as below:

Is sleep-wake cycle and sleep duration culturally determined? Comparison of Tibetan and Japanese children's Sleep

Comments on the Quality of English Language

The introduction misses some focus; it talks a lot about the importance of sleep (two paragraphs), but that is not what the article is about - as no health outcomes ar being tested. 

Thank you for your comment. As you point out, mentioning health may not make the point of this article clear. We have deleted the sentences and returned to the original text.

Recently, the importance of sleep in brain development has been reported. The pruning of excess synapses for learning and memory consolidation occurs during sleep [1-3]. Synaptogenesis and pruning are most active during early childhood [4]. European large birth cohort studies suggest that sleep problems in infancy, such as short sleep duration, frequent awakenings after sleep onset, late bedtimes, and irregularity of sleep patterns, are risk factors for high scores on attention deficit hyperactivity disorder and lower language acquisition at age 5-6 years, as well as depressive and psychotic symptoms in adolescence [5-7]. Getting enough and good quality sleep is especially important in the early years of childhood. (line 28-36)