Peer Review Article on How Can Adolescents Improve Their Sleep

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Open Access

Peer-reviewed

Inquiry Article

Total Sleep Time Severely Drops during Adolescence

• Damien Leger,
• François Beck,
• Jean-Baptiste Richard,
• Emmanuelle Godeau

10

• Published: October 17, 2012
• https://doi.org/10.1371/journal.pone.0045204

Figures

Abstract

Restricted sleep elapsing amongst immature adults and adolescents has been shown to increment the take a chance of morbidities such as obesity, diabetes or accidents. All the same there are few epidemiological studies on normal full sleep time (TST) in representative groups of teen-agers which let to get normative data.

Purpose

To explore perceived total sleep time on schooldays (TSTS) and not schooldays (TSTN) and the prevalence of sleep initiating indisposition amid a nationally representative sample of teenagers.

Methods

Data from 9,251 children anile 11 to 15 years-old, 50.7% of which were boys, equally part of the cross-national study 2011 HBSC were analyzed. Self-completion questionnaires were administered in classrooms. An estimate of TSTS and TSTN (calendar week-ends and vacations) was calculated based on specifically designed sleep habits study. Sleep deprivation was estimated past a TSTN – TSTS divergence >ii hours. Sleep initiating nsomnia was assessed according to International nomenclature of slumber disorders (ICSD 2). Children who reported sleeping 7 hours or less per night were considered as brusk sleepers.

Results

A serious driblet of TST was observed between 11 yo and fifteen yo, both during the schooldays (9 hours 26 minutes vs. 7 h 55 min.; p<0.001) and at a lesser extent during week-ends (10 h 17 min. vs. nine h 44 min.; p<0.001). Sleep deprivation concerned sixteen.0% of chidren aged of 11 yo vs. xl.5% of those of 15 yo (p<0.001). Too short sleep was reported by two.six% of the eleven yo vs. 24.half-dozen% of the 15 yo (p<0.001).

Conclusion

Despite the obvious demand for sleep in adolescence, TST drastically decreases with historic period among children from 11 to 15 yo which creates meaning sleep debt increasing with age.

Citation: Leger D, Beck F, Richard J-B, Godeau East (2012) Total Sleep Time Severely Drops during Boyhood. PLoS I 7(ten): e45204. https://doi.org/10.1371/journal.pone.0045204

Editor: Namni Goel, University of Pennsylvania School of Medicine, Us of America

Received: January 31, 2012; Accepted: August 17, 2012; Published: October 17, 2012

Copyright: © Leger et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted employ, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This study was supported by INPES (Institut National de Prévention et d'éducation cascade la Santé) (French national Institute of prevention and wellness instruction) and INSERM. Internationally, it was supported past the WHO (Worl Health Arrangement). The funders had no role in study pattern, data collection and assay, decision to publish, or preparation of the manuscript.

Competing interests: The authors accept alleged that no competing interests be.

Introduction

Sleep is recognized equally a major contributing cistron to physical and mental health in humans, particularly in young adults. Although the precise functions of slumber are not entirely understood, crucial studies have demonstrated its critical function in many of import somatic, cerebral, and psychological processes. For example, it is believed that sleep is benign for energy conservation, neuronal recuperation, and brain plasticity [one]–[four]. Sleep has been shown to play a major office in the metabolic, cardiovascular, respiratory, immune and thermoregulatory processes which contribute to daytime brain functioning and body homeostasis. Slumber is likewise essential for growth, as growth hormone is selectively secreted during ho-hum moving ridge sleep [1]–[2], [4]–[5]. Beside these metabolic functions, sleep is mainly involved in cerebral and psychological processes, including learning and memory consolidation, as well as emotional memory and processing [6]–[eleven].

Acute and chronic slumber deprivation studies have reinforced the belief that sleep is essential to good concrete and mental wellness. Chronic sleep deprivation, (defined as sleeping 50%–75% of a normal 8 h nighttime'due south sleep for several successive nights) alters vigilance, cognition and mood, causes anxiety and increases the adventure of accidents [12]–[xiv]. Chronic 'too brusk sleep' (less than 6 hours per 24 hours in adults) is associated with an elevated risk of diabetes, overweight, and cardiovascular diseases [xv]–[17]. Acute sleep deprivation (defined every bit sleeping 25–fifty% of a normal 8 h night'southward sleep) contributes to increased inflammation and disturbs the immunological response [18]–[20]. As adolescence is considered a specially vulnerable menses during which physiological, psychological and cerebral processes undergo maturation, it could be hypothesised that curt sleep and sleep impecuniousness would accept a worse effect in this group than in young adults both in the brusk and in the long terms.

Even so, there are several studies, generally made in urban settings, showing that teens have ofttimes a too short amount of sleep during calendar week-days: In Taiwan, 1939 adolescent aged from 12 to 16 years old have been interviewed at schools in the Lin-Kou district [21]. Their mean (SD) sleep elapsing on weekdays was 7.35 (ane.23) hours and ix.38 (i.62) hours on weekends. Weekday's night slumber decreased significantly when school grade increased (6.87 hours (ane.xiv) for high school seniors). In Iceland, a group of 668 adolescents (aged 11, 13, and 15) were followed longitudinally three times, every 5 years. Iceland teens had delayed bedtimes and shorter nocturnal sleep during the week increasing with age [22]. The HELENA study also interviewed adolescents from x European cities in Austria, Belgium, France, Germany, Greece, Hungary, Italia, Spain and Sweden about their sleep duration. It institute a rather low averaged total sleep time effectually 8 hours per twenty-four hour period [23]. In Korea, a 2638 sample of urban high school students, aged from 14 to 17 years old (yo), self-reported sleep schedules and habits during weekdays and week-ends and performed attending tasks [24]. Their hateful (SD) slumber duration on weekdays was 5 hours 42 minutes (1 hour 0 minutes) per twenty-four hour period and on weekends: 8 hours 24 minutes (1 hour 36 minutes) per twenty-four hours. In Brazil, brusk sleep elapsing was also found increased with historic period in a 4452 adolescents grouping of Pelotas (anile x–12 years) participating in a prospective nascency cohort [25]. Using less than vi hours to define short sleep, a longitudinal 1 yr survey of iv,175 adolescents aged from 11 to 17years erstwhile living in Texas, establish an impressive charge per unit of twenty% of short sleepers [26]. Conversely, a Canadian longitudinal sleep study testing the link between body mass index (BMI) and full fourth dimension spent in bed (according to female parent's testimony), found a rather college time spent in bed, in the 10 yo children [27]. They were estimated to stay in bed a mean (SD) time of x.2 (0.6) hours at 10 yo and 9.ix (0.6) hours at 13 yo.

All these studies showed that curt sleep was mutual in adolescents in many parts of the globe. Notwithstanding defining brusque sleep or sleep deprivation in adolescents is fabricated difficult by the limited number of studies which focus on normative data in nationally representative groups of adolescents. One meta-analysis of objective quantitative sleep parameters, from childhood to old age in healthy individuals, has calculated based on 18 studies including a total of 1360 children full sleep time, assessed by polysomnography (the gold standard physiological measure out of sleep) [28]. The authors showed that total slumber fourth dimension varied widely amidst the studies: from 8 to 9 hours and 30 minutes at the historic period of 11; and from 7 to eight hours and twoscore minutes at xv. These studies, even so, were examining slightly unlike age groups using dissimilar measurement techniques in unlike countries, all of which could contribute to differences in result. A nationally representative survey, the American Sleep University Task Strength, America poll in 2006 has constitute that teenagers aged 12 and thirteen yo (vii^th and 8^th course) were reporting an average of 8 hours total sleep fourth dimension on school nights and 15 yo were reporting 7.25 hours. They also showed that sleep during not school days was longer and did non vary much from xi to 15 yo (over 9 hours of sleep). This study may help to better understand what are normative values of sleep in adolescents in the USA [29].

However, to prevent sleep deprivation in adolescents more extensive knowledge is required well-nigh their existent sleeping habits in unlike countries.. These normative information are however essential if nosotros want to define "too short sleep" or "sleep impecuniousness" and their association with co-morbidities. The aim of this study was therefore to obtain normative information on full sleep time, sleep habits and insomnia in adolescents anile eleven to fifteen in French republic, in a large and nationally representative sample of subjects.

Methods

Sampling Design

Analyses were based on a nationally representative, cross-sectional sample of students from France, collected within the cantankerous-national health behaviour in schoolhouse-aged children survey (HBSC) and conducted under the auspices of the World Health Organisation. By 2010, 42 European and Northern American countries and regions were included [xxx]–[32]. A mutual HBSC report protocol standardizes instrumentation, sampling methods, and data collection procedures in each country, with information cleaning and data set up construction performed centrally.

Every bit the student sample is clustered into schools and classrooms, it is necessary to take into business relationship the effects of clustering on the potential homogeneity of data within selected schools and classrooms. Students aged 11, 13, and 15 years were targeted (mean ages: 11.5, 13.5, and 15.5 years) broadly covering the onset and the middle years of adolescence, when controlling begins [xxx].

In guild to reaching the international requirement to obtain a 95% conviction interval for a proportion of 50% by age grouping, and under the hypothesis of an reply rate of fourscore% a full of 367 schools were randomly sampled at national level, and 347 were included in the French 2010 HBSC sample. This sample was stratified according to three criteria: the urbanity level of the metropolis where the school was located, the class academic level and the private/public status of the school. It was therefore congenital to stand for the socio-demographic characteristics of the French national population of this age group [30]–[32].Data were collected using standardized self-completion questionnaires administered in classes during Spring 2010.

Ethics

Participation was anonymous and voluntary; consent was obtained from both parents and students. The study protocol was approved past the Ministry of Didactics ethical national review board for surveys involving people and data management (Comité d'éthique du Minsitère de 50'Education Nationale) and the French National Commission on It and Liberties (Committee Nationale Informatique et Libertés (CNIL)).

A personal letter was sent to each parent (carer) to explain the study and become their approval. If they consent they did not have to answer (passive consent). If they did not consent they had to complete a written document and send it to their kid'south school with prepaid mail. Ethics committees approved this consent process.

Children had also to give their written consent, putting their signature on a name list which was provided by the teachers. This process allowed confidentiality of the questionnaires. If they did not consent, they were allowed to do other school activities in a separate room from children participating to the written report to manage silence and self concentration. Ethics committees approved this consent process.

Measurements

Sections investigating sleep habits were introduced in the French HBSC for the first fourth dimension in 2010. From previous studies [30]–[32] specific sleep investigations were tested and piloted in France along with the standard HBSC questionnaire on health, health behaviour and their determinants and broader context. These slumber-specific measurements were inspired from validated tools recommended for the assessment of sleep in adolescence such as enquiring specifically about and separating sleep on school nights to sleep on weekends and using diaries to keep a log of slumber hours [33]–[34]. As our survey was designed to be fabricated on a unmarried day, we used single particular sleep habit reports to appraise full slumber time. The following information was collected:

1. An judge of the total slumber fourth dimension (TST) during the schooldays (TSTS) and during non schooldays (week-ends or non school days) (TSTN) was based on the post-obit questions:
   
   1. 'When you have/don't have class the following day, at what time practice y'all commonly go to bed?' with 13 possible answers for each question: "non after 9 p.m.", around ix.thirty p.yard., around 10 p.m., around x.xxx p.m.; effectually 11 p.g., around 11.30 p.chiliad., around midnight, around 12.xxx a.m., effectually 1 a.one thousand., effectually 1.xxx a.m., around 2 a.m., effectually two.30 a.m., "3 a.chiliad. or later". When the subjects ticked off "not after 9 p.m.": we entered 9 in our calculation and when they ticked off "three a.m. or later": we entered three.
   2. 'When yous take/don't accept grade the following twenty-four hour period, at what time practice you usually wake up?' with xv possible answers for each question "non later 5 a.m. around 5.30 a.m., around 6 a.yard., around six.30 a.m., around vii a.m., effectually 7.30 a.grand., around eight a.m., around 8.thirty a.k., effectually 9 a.m., around 9.30 a.thousand., around ten a.m., around 10.30 a.thou., around xi a.grand., around 11.30 a.m., apex or after noon". When the subjects ticked off "non subsequently 5 p.chiliad.": we entered five in our calculation and when they ticked off "noon of after noon": we entered 12.
   3. 'Unremarkably how long does information technology take for you to fall comatose?' with 5 possible answers: "less than 10 minutes", "from eleven to 20 minutes", "from 21 to 30 minutes", "from 31 to xl minutes", "more than twoscore minutes". When a subject ticked off "less than 10 minutes" nosotros entered 10, "from xi to 20 minutes" we entered 15, "from 21 to xxx minutes" we entered 25, "from 31 to forty minutes" nosotros entered 35, "more twoscore minutes" we entered 40.
   TST was divers as the deviation between the time at which the participant went to bed and the fourth dimension of the day they wake up, discounting the time needed to fall asleep.

1. Sleep problems were defined equally follows:
   1. "Sleep initiating problems": There is a lack of consensual definition of indisposition in children. In early on childhood it is important to take account of and utilize parents every bit witnesses [35]. Notwithstanding teenagers are more than probable to answer to the same definition than adults, which was proposed past international consensus groups [36]–[37]. Based on these we considered that our subject had "sleep initiating bug" when they answered "every night" or "several times per calendar week" to the question "Have yous had trouble falling asleep during the last half dozen months?" They were considered to have daytime consequences of poor slumber when they answered "more than 4 times a calendar week" or "2 or three times a calendar week" to the question: "Do yous feel tired when you wake upwardly on days you have form?".
   2. "Sleep debt": Despite the absence of a consensual definition for sleep debt in adolescents, most authors and the National sleep Foundation in the United states consider that a "ii hours debt" was sufficient enough to evoke slumber debt in teenagers [38]–[41]. We therefore defined sleep debt in our subjects every bit a difference between TSTN and TSTS for over 2 hours.
   3. 'Also short slumber': In adults, subjects sleeping less than 6 hours during the weekdays are ordinarily considered "short sleepers" and may potentially be at college risk of developing co morbidities [17]. In teenagers, based on previous recommendations and observations, we considered that sleeping 7 hours or less was "too short" [21]–[28], [38].

Statistical Analysis

Information nerveless were weighted using national data concerning sex, age and student academic levels distribution, in order to being representative of the French pupil teenager population. Analysis Data management and statistical analysis were performed using the R software (version two.12.1). Reported differences were meaning at the 0.01 level or less. The Holm-Bonferroni method has not been used for multiple comparisons. Nerveless data were analyzed in the total population and separately for boys and girls, equally significant associations were initially found betwixt gender and TST. An Analysis of Variance (ANOVA) was performed to test the deviation betwixt the mean outcome scores across the different age groups. Comparisons between groups of full slumber time were too made using student ANOVA for continuous data and chi-squared test for categorical data.

Results

Response rates at school were 93.five%. Out of 9251 students (4643 boys and 4608 girls participated to the study), students' non response was due to parental refusal (7.7%), student refusal (1.2%) and absence of the student the twenty-four hour period of the survey (seven.3%). Non respondents were not significantly unlike from respondents for age and sexual practice. They were significantly different regarding socio-demographic profiles. Those figures are in line with those observed in other European countries in such school surveys. Due to the design of the study, this sample was representative of the full general group of adolescents of France.

Full sleep fourth dimension (Tabular array ane)

TSTS decreased continuously and significantly from an average of nine hours (h) 26 minutes (min) (3 min) among 11 twelvemonth-olds to an average 7 h 55 min (three min) amid 15 year-olds (p<0.001). Tabular array 1 shows that, in both genders, TSTS decreased with an boilerplate of 20 min per year and a total difference mean of ane h 31 min betwixt ages 11 and fifteen (p<0.001).

TSTN also significantly declined in the total group of students, from x h 17 min (4 min) at historic period 11 to nine h 44 min (4 min) at age 15 (p<0.001). The pass up is not as steep as TSTS, but significant.

The average TSTN was greater in girls (10 h 12 min (2 min) vs. ix h 50 min (2 min) in boys, p<0.001).

Slumber initiating issues

Sleep initiating issues were reported by a significantly higher percentage of young subjects of the total group when age increased: 16.5% of the 11 yo, vs. 20.viii% of the 15 yo (p<0.001 among age groups). In boys no significant departure was still plant among ages. In girls the difference was highly significant (18.3% of the 11 yo, vs. 25.5% of the 15 yo; p<0.001 among age groups).

Sleep debt and too curt sleep

Slumber debt, which was defined by a TSTN –TSTS divergence greater than ii hours increased significantly and steadily between xi and 15, concerning 16.0% of 11 yo and up to 40.5% of those aged 15 yo (p<0.001). Slumber debt was higher in girls in each historic period group and globally (31.9% of girls vs. 22.one% of boys, p<0.001).

'Too brusk sleep' (TSTS<vii h) also increased gradually and significantly as information technology was reported past 24.6% of the xv yo vs. ii.6% of the 11 yo (p<0.001). This occurred in both genders (23.7% of the fifteen yo vs. three.0% of the 11 yo boys (p<0.001) and respectively 25.4% and 2.1% among girls (p<0.001)).

Discussion

Despite increasing evidence that sleep debt is a mutual behaviour in adolescents and several epidemiological studies made across the planet on adolescents sleep debt and recovery [21]–[27], there were, to our knowledge, except one important call survey made in 2006, in the Usa [28], very few epidemiological surveys producing normative data on sleep length in a national representative group of teenagers and none in France. Such data would be a helpful tool in helping parents and kids carers on health education and prevention rules for preserving sleep in adolescents. Recommendations currently given to caregivers apropos sleep requirements in adolescence have increased the awareness of public health authorities in the field of education and children's health [38]–[xl]. According to the US National Institute of Health, sleep requirements for teenagers and preteens are estimated to exist between x hours for 12 yo and viii.5 hours for xviii yo [xl]. Co-ordinate to the World Wellness Organisation function in Europe, adolescents need betwixt ix and 10 hours of slumber per mean solar day [41]. One major finding of our written report is that teenagers are ordinarily sleeping less than is expected. We found that children at 12 yo are more likely to sleep 9 hours and those of 15 yo; 8 hours. An even more severe reduction of TST in teenagers was previously reported past written report of the American Sleep University Task Force, America poll in 2006 [29]. Children were interviewed by telephone (in the presence of their caregivers who were as well interviewed) [42]. Information technology was found that teenagers aged 12 and xiii yo (7^th and 8^th grade) were reporting an average of 8 h of total sleep time on schoolhouse nights and xv yo were reporting 7.25 h. They also showed that slumber during non schoolhouse days was longer and did not vary much from eleven to 15 yo (over nine h of sleep). Our study confirms, in an epidemiological setting, that total sleep time decreased severely during boyhood. Several authors take previously reported and reviewed this slumber reduction as information technology seems contradictory considering adolescents' high sleep requirements at this crucial period of their lives [21]–[27], [42]. This sleep reduction was indeed found in different cultures like Korea (with a mean sleep duration on weekdays of v h 42 min (1 h 0 min) per day and on weekends of eight h 24 min (1 h 36 min) per twenty-four hours) [24]. We already reported the aforementioned kind of results in Brazil, in Texas (with twenty% of kids sleeping less than 6 h during schooldays), in Taipei and in Iceland [21]–[22], [25]–[26]. Sleep loss through adolescence is indeed not driven past a reduction in sleep requirements only arises from a convergence of biologic, psychological, and socio-cultural influences [43].

Another stiff point of this study is the collaboration with the HBSC which covered a representative sample of students and delivered confidential questionnaires to the students. Parents' testimonies are well known to not reverberate the real sleep habits of teenagers. Endmost the bedroom door and saying "goodnight" does not ensure that the kid falls comatose immediately [44]–[45]. The older children become, the less parents accurately capture night time habits [45]. It was the strength of our written report: to straight and confidentially interview children (without the presence of their parents) on their sleep and sleep problems. Moreover nosotros carefully designed and piloted questions that had not been previously extensively used in this population to capture authentic times for going to sleep and enkindling as well as sleep latency, on schooldays and non schooldays evenings. Interviewing students rather than their parents may explain the differences found between our results and those published in other recent studies, which based on parents' reports. In a representative sample of 1916 Canadian preadolescents, authors found, based on weekly assessments over six months that the development of weekday time in bed (TIB) decreased from a hateful of 10 h and 29 min (32 min) per 24-hour interval at x yo to ix h and 29 min (37 min) per day at 13 yo. They therefore considered as short sleepers participants who slept less than 10 hours per day [27]. In the Sleep in America survey on Teens, parents curiously reported an increment in TIB from 11 yo (9 h50 min), to xv yo (10 h 43 min), which reflects the discrepancy between parents and adolescents perceptions of fourth dimension in bed and slumber time [42]. Equally mentioned by several authors the bulk of parents are unaware of their adolescents' sleeping patterns [44]–[45].

In this study we besides attempted to clarify how sleep debt or too short slumber may be divers in adolescents. Chronic sleep deprivation in adults is known to be associated with poor vigilance, cognition and mood besides as promotes anxiety and a college run a risk of accidents [12]–[xiv]. Chronic 'as well short sleep' (less than 6 hours per 24 hours) leads to an increased risk of diabetes, raised BMI and cardiovascular diseases [16]–[21]. In adolescents several contempo studies showed like links: 'also brusk sleep' was associated with raised BMI, diabetes, depression, fatigue and suicidal thoughts [23]–[27], [42], [46]–[49]. Notwithstanding these final studies failed to concord on consensual definitions of 'too brusque slumber' and 'sleep debt' in adolescents. In our report, we proposed a definition for 'sleep debt' in adolescents (defined past a TSTN –TSTS difference greater than two hours) and 'also brusque sleep' (TSTS<7 hours)) based on naturalistic and non clinical databases. We also considered that sleeping less than vii hours may be considered as "too short sleep". The data revealed an impressive increased in students concerned past these ii problems: slumber debt concerned 16% of the 11 yo group and 40.5% of the fifteen yo whereas 'also short slumber' was complained of by two.six% of the 11 yo and 24.half dozen% of the 15 yo. Even so we sympathise that the cutoff of 7 hours may be controversial. Thus, boosted rationale for the use of this cutoff in this population is warranted. Laboratory studies data regarding sleep extension, grades, assesment of sleepiness by objective tests such every bit Multiple sleep latency test (MSLT) would be helpful to validate this cutoff.

All the same we acknowledge that at that place are several limitations to our study. This study is a not longitudinal, cross sectional survey. Sleep was assessed once during the year and could not exist considered as representative of slumber habits over the year. Moreover we used subjective questionnaires to assess sleep and acknowledge that polysomnography is the only objective gold standard method to assess sleep quality and quantity [37]. Several studies carried out in adolescents used actigraphy as well as questionnaires. Nevertheless several of these studies showed that the sleep logs and questionnaires used to assess sleep patterns in adolescents used in our study are also validated tools to accurately gauge sleep duration in teenagers [22], [43]–[45]. We recognize that nosotros only focussed on total slumber fourth dimension with no consideration for physical or psychological diseases which could influence private and collective slumber. This was not the aim of this study every bit we prioritised collecting normal data on sleep patterns in a representative sample of the adolescents. However futurity studies should aim to focus on the determinants and correlates which may influence full sleep time in this crucial period of the life.

Author Contributions

Conceived and designed the experiments: DL FB JBR EG. Performed the experiments: FB EG. Analyzed the data: DL FB JBR EG. Contributed reagents/materials/analysis tools: DL FB JBR EG. Wrote the paper: DL FB JBR EG.

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