ABSTRACT:

Objective:

This study aimed to investigate the association between sleep duration and excess weight in Brazilian adolescents.

Methods:

This is a cross-sectional study conducted with 65,837 adolescents, aged 12 to 17 years, enrolled in the Study of Cardiovascular Risks in Adolescents (ERICA). Sleep duration was assessed by means of a questionnaire focusing on weekday and weekend hours of sleep. Nutritional status was assessed based on body mass index, and participants were classified according to age and gender. The statistical analysis was performed with the Stata 13 software, using the survey command. Poisson regression was used to determine the association of excess weight with sleep duration categories.

Results:

A decline in sleep duration was associated with advancing age. The prevalence of short and long-term sleep among adolescents was 17.9 and 3.6%, respectively, while overweight was diagnosed in 25.5% of the sample. Adolescents who reported having short sleep had 10% (PR = 1.10; 95%CI 1.06 – 1.15) more overweight, while those who reported sleeping more than 11 hours had approximately 12% (PR = 0.88; 95%CI 0.78 – 0.99) less excess weight.

Conclusion:

Our findings reinforce the assumption that insufficient sleep poses health risks, and encouraging regular and sufficient sleep may be a cost-effective intervention for the prevention of overweight in adolescence.

Keywords:
Sleep; Overweight; Obesity; Adolescent; Body mass index

INTRODUCTION

Overweight in childhood and adolescence has recently reached alarming proportions¹1. Afshin A, Forouzanfar MH, Reitsma MB, Sur P, Estep K, Lee A, et al. Health effects of overweight and obesity in 195 countries over 25 years. N Engl J Med 2017; 377(1): 13-27. https://doi.org/10.1056/nejmoa1614362
https://doi.org/10.1056/nejmoa1614362... and became a major public health challenge worldwide²2. World Health Organization. Consideration of the evidence on childhood obesity for the Commission on Ending Childhood Obesity: report of the Ad hoc Working Group on Science and Evidence for Ending Childhood Obesity. Genebra: World Health Organization; 2016.. High prevalences have been confirmed in international³3. Ng M, Fleming T, Robinson M, Thomson B, Graetz N, Margono C, et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2014; 384(9945): 766-81. https://doi.org/10.1016/s0140-6736(14)60460-8
https://doi.org/10.1016/s0140-6736(14)60... and national⁴4. Leal MABF, Paiva SSC, Sousa SSL, Lima CEB, Silva ARV, Nascimento FF, et al. Fatores sociodemográficos e comportamentais associados ao excesso de peso em adolescentes brasileiros – 2015. Adolesc Saúde 2019; 16(2): 16-26. studies, which demonstrates the need for action by several protagonists to expand programs that encourage the prevention of the problem as well as interventions.

Known as a nutritional disorder of multifactorial origin⁵5. Hebebrand J, Hinney A. Environmental and genetic risk factors in obesity. Child Adolesc Psychiatr Clin N Am 2009; 18(1): 83-94. https://doi.org/10.1016/j.chc.2008.07.006
https://doi.org/10.1016/j.chc.2008.07.00... , whose interactions between potential determining factors — with emphasis on social, environmental and behavioral domains — impact health directly, leading to relevant increases in chronic non-transmissible diseases, especially in adulthood⁶6. He F, Rodriguez-Colon S, Fernandez-Mendoza J, Vgontzas AN, Bixler EO, Berg A, et al. Abdominal obesity and metabolic syndrome burden in adolescents - Penn State Children Cohort study. J Clin Densitom 2015; 18(1): 30-6. https://doi.org/10.1016/j.jocd.2014.07.009
https://doi.org/10.1016/j.jocd.2014.07.0... .

Short sleep duration — a modifiable risk factor — has been identified as one of these factors proven to have an association with the increased prevalence of overweight in adolescence⁷7. Ruan H, Xun P, Cai W, He K, Tang Q. Habitual Sleep Duration and Risk of Childhood Obesity: Systematic Review and Dose-response Meta-analysis of Prospective Cohort Studies. Sci Rep 2015; 5: 16160. https://dx.doi.org/10.1038%2Fsrep16160
https://dx.doi.org/10.1038%2Fsrep16160... .

This can be explained by the change in the production and release of several hormones such as leptin, insulin, cortisol, ghrelin and growth hormones, which play an important role in signaling the hypothalamic centers that regulate food intake and energy balance⁸8. Taheri S. The link between short sleep duration and obesity: we should recommend more sleep to prevent obesity. Arch Dis Child 2006; 91(11): 881-4. https://dx.doi.org/10.1136%2Fadc.2005.093013
https://dx.doi.org/10.1136%2Fadc.2005.09... ^,99. Leproult R, Van Cauter E. Role of Sleep and Sleep Loss in Hormonal Release and Metabolism. Endocr Dev 2010; 17: 11-21. https://doi.org/10.1159/000262524
https://doi.org/10.1159/000262524... . In addition, daytime sleepiness and fatigue as a result of short sleep duration can alter eating behaviors and physical activity, potentially leading to weight gain⁸8. Taheri S. The link between short sleep duration and obesity: we should recommend more sleep to prevent obesity. Arch Dis Child 2006; 91(11): 881-4. https://dx.doi.org/10.1136%2Fadc.2005.093013
https://dx.doi.org/10.1136%2Fadc.2005.09... . It could also lead to weight gain simply because people who stay awake longer would have more opportunities to eat, which makes the maintenance of a healthy lifestyle more difficult⁸8. Taheri S. The link between short sleep duration and obesity: we should recommend more sleep to prevent obesity. Arch Dis Child 2006; 91(11): 881-4. https://dx.doi.org/10.1136%2Fadc.2005.093013
https://dx.doi.org/10.1136%2Fadc.2005.09... ^,1010. Chaput JP, Tremblay A. Insufficient sleep as a contributor to weight gain: an update. Curr Obes Rep 2012; 1: 245-56. https://doi.org/10.1007/s13679-012-0026-7
https://doi.org/10.1007/s13679-012-0026-... .

A recent meta-analysis on data from more than 56 thousand children and adolescents up to 16 years of age pointed out that participants who had shorter sleep time were 76% more likely to be diagnosed with overweight compared to those with longer sleep time, in addition to showing greater gain body mass index (BMI). However, an increase of one hour in daily sleep was capable of reducing the risk of overweight and obesity by 21%⁷7. Ruan H, Xun P, Cai W, He K, Tang Q. Habitual Sleep Duration and Risk of Childhood Obesity: Systematic Review and Dose-response Meta-analysis of Prospective Cohort Studies. Sci Rep 2015; 5: 16160. https://dx.doi.org/10.1038%2Fsrep16160
https://dx.doi.org/10.1038%2Fsrep16160... .

A longitudinal Brazilian study conducted by Halal et al.¹¹11. Halal CS, Matijasevich A, Howe LD, Santos IS, Barros FC, Nunes ML. Short sleep duration in the first years of life and obesity/overweight at age 4 years: a birth cohort study. J Pediatr 2016; 168: 99-103.e3. https://doi.org/10.1016/j.jpeds.2015.09.074
https://doi.org/10.1016/j.jpeds.2015.09.... showed that the prevalence of short sleep duration in any follow-up from the first to the fourth year of age was 10.1% and, at 4 years of age, 5.3% of children were diagnosed with obesity and 8% were overweight among those who slept little, with a prevalence ratio for overweight after adjustment for maternal and infant characteristics was 1.32.

The association between short sleep duration and weight gain has been the subject of several studies, initially with the adult population, but nowadays it was also extended to younger age groups. However, in Brazil, a population-based study that would investigate sleep duration as a health risk condition was not conducted yet.

Given the above, this study aimed to investigate the association between short sleep duration and excess weight in a representative portion of Brazilian adolescents enrolled in schools.

METHODS

This study used data from the nationwide epidemiological survey with cross-sectional design entitled “Study of Cardiovascular Risks in Adolescents” (ERICA, in the Portuguese acronym), conducted in 2013 and 2014. The sample was composed of adolescents aged 12 to 17 years enrolled in public and private schools in Brazilian municipalities with more than 100 thousand inhabitants.

Schools were selected with probability directly proportional to their size and inversely proportional to the distance from the capital. In each school previously drawn, the groups were selected based on a combination of period (morning and afternoon) and eligible years (seventh, eighth and ninth years of elementary school and first, second and third years of high school), with one class from each combination of period and year selected with equiprobability¹²12. Vasconcellos MTL, Silva PLN, Szklo M, Kuschnir MCC, Klein CH, Abreu GA, et al. Sampling design for the Study of Cardiovascular Risks in Adolescents (ERICA). Cad Saúde Pública 2015; 31(5): 921-30. https://doi.org/10.1590/0102-311X00043214
https://doi.org/10.1590/0102-311X0004321... .

Of the selected classes, all students aged 12 to 17 years old were invited to participate, except adolescents with any physical disability that would prevent anthropometric assessment, mental disability and pregnant girls.

Data collection was conducted using standardized techniques by a previously trained team of evaluators, in which anthropometric measurements, blood pressure, 24-hour food recall and laboratory blood tests were performed. The other information was collected by means of a questionnaire, applied to students in the classroom, by means of an electronic collector named personal digital assistant (PDA). The complete study protocol is described by Bloch et al.¹³13. Bloch KV, Szklo M, Kuschnir MC, Abreu GA, Barufaldi LA, Klein CH, et al. The Study of Cardiovascular Risk in Adolescents-ERICA: rationale, design and sample characteristics of a national survey examining cardiovascular risk factor profile in Brazilian adolescents. BMC Public Health 2015; 15: 94. https://doi.org/10.1186/s12889-015-1442-x
https://doi.org/10.1186/s12889-015-1442-... .

The outcome of overweight was assessed by calculating BMI (weight/height²2. World Health Organization. Consideration of the evidence on childhood obesity for the Commission on Ending Childhood Obesity: report of the Ad hoc Working Group on Science and Evidence for Ending Childhood Obesity. Genebra: World Health Organization; 2016.) and the classification of nutritional status was established according to recommendations by the World Health Organization (WHO)¹⁴14. de Onis M, Onyango AW, Borgi E, Siyan A, Nishida C, Siekmann J. Development of a WHO growth reference for school-aged children and adolescents. Bull World Health Organ 2007; 85(9): 660-7. https://doi.org/10.2471/blt.07.043497
https://doi.org/10.2471/blt.07.043497... , with cut-off points specific to sex and age. The adolescents classified as very low weight and low weight were put in the group “Low Weight”, and those diagnosed with overweight and obesity, were allocated in the group “Excess Weight”.

Sociodemographic and school-related variables were used to adjust the analyses: sex (girls and boys), age group (12–14; 15–17 years), self-reported race/color (white, black and mixed race/yellow/indigenous), mother’s educational level in years of study (<8 or ≥8), type of school (public and private), study period (morning and afternoon) and school region (urban and rural).

The level of physical activity was determined using a questionnaire in a validated version for Brazilian adolescents¹⁵15. Sallis JF, Strikmiller PK, Harsha DW, Feldman HA, Ehlinger S, Store EJ, et al. Validation of interviewer-and self-administered physical activity checklists for fifth grade students. Med Sci Sports Exerc 1996; 28(7): 840-51. https://doi.org/10.1097/00005768-199607000-00011
https://doi.org/10.1097/00005768-1996070... . The instrument consists of a list of 24 types of activities, in which the adolescents should choose the frequency in days and the time in hours and minutes that they had practiced that activity in the last week. Adolescents who did not accumulate at least 300 min/week of physical activity were considered inactive, as indicated by WHO¹⁶16. World Health Organization. Global recommendations on physical activity for health. Genebra: World Health Organization; 2010..

According to the criteria proposed by Marshall and Tanner¹⁷17. Marshall WA, Tanner JM. Variations in pattern of pubertal changes in girls. Arch Dis Child 1969; 44(235): 291-303. https://dx.doi.org/10.1136%2Fadc.44.235.291
https://dx.doi.org/10.1136%2Fadc.44.235.... ^,1818. Marshall WA, Tanner JM. Variations in the Pattern of Pubertal Changes in Boys. Arch Dis Child 1970; 45(239): 13-23. https://dx.doi.org/10.1136%2Fadc.45.239.13
https://dx.doi.org/10.1136%2Fadc.45.239.... , the stage of sexual maturation was self-assessed through visualization and selection of illustrative figures arranged in the PDA, according to the sex of the adolescent. The stages were classified into: stage 1 for pre-pubertal development; stages 2, 3 and 4, which correspond to the progression of puberty; and stage 5, complete maturation.

Sleep duration was investigated by four questions about the time the teenager used to go to sleep and wake up on a typical weekday and during weekends, with 24 response options. The inconsistencies in the response patterns were analyzed and corrected based on the most frequent times and the student’s study period, as described in a previous publication¹⁹19. Abreu GA, Silva TLN, Teixeira LR, Block KV. Análise da qualidade da informação autorreferida sobre duração do sono de escolares do Estudo de Riscos Cardiovasculares em Adolescentes (ERICA). Cad Saúde Pública 2019; 35(10): e00152918. https://doi.org/10.1590/0102-311x00152918
https://doi.org/10.1590/0102-311x0015291... . The variable sleep duration (hours) was obtained by the difference between usual bedtime and wake-up time, considering common weekdays and weekends. A weighted average of the duration of sleep per week was calculated using the formula: (sleep during the week × 5 + sleep at the weekend × 2)/720. As recommended by the National Sleep Foundation²¹21. Hirshkowitz M, Whiton K, Albert SM, Alessi C, Bruni O, DonCarlos L, et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health 2015; 1(1): 40-3. https://doi.org/10.1016/j.sleh.2014.12.010
https://doi.org/10.1016/j.sleh.2014.12.0... , a short sleep duration was considered <7 hours and long sleep duration >11 hours. Therefore, the duration of inconsistent sleep was disregarded from the analysis when, during the week and the weekend, the adolescents reported sleeping <4 hours and >14 hours, maximum limits of what is considered appropriate for the age group¹⁹19. Abreu GA, Silva TLN, Teixeira LR, Block KV. Análise da qualidade da informação autorreferida sobre duração do sono de escolares do Estudo de Riscos Cardiovasculares em Adolescentes (ERICA). Cad Saúde Pública 2019; 35(10): e00152918. https://doi.org/10.1590/0102-311x00152918
https://doi.org/10.1590/0102-311x0015291... .

The data were analyzed in the statistical package Stata, version 13.0, whose survey mode was applied due to the complex design of the sample. The prevalence estimates were presented in proportions (%), with respective 95% confidence intervals (95%CI). The χ²2. World Health Organization. Consideration of the evidence on childhood obesity for the Commission on Ending Childhood Obesity: report of the Ad hoc Working Group on Science and Evidence for Ending Childhood Obesity. Genebra: World Health Organization; 2016. test was used to assess the difference between the prevalence of sleep duration accordingly and the other variables in overweight adolescents.

The association between excess weight and sleep duration was analyzed using regression models in two stages: first, bivariate regressions of the independent variables in relation to the outcome, with results p<0,20 in the χ²2. World Health Organization. Consideration of the evidence on childhood obesity for the Commission on Ending Childhood Obesity: report of the Ad hoc Working Group on Science and Evidence for Ending Childhood Obesity. Genebra: World Health Organization; 2016. test being selected for the multivariate model. Then, models were used to obtain the prevalence rates of excess weight for each category of sleep duration, using the group of adolescents from 7 to 11 hours of sleep as a reference. The Poisson regression was used to calculate crude and adjusted prevalence ratios (PR) and respective 95%CI. The adjusted analyses verified the association between excess weight and the categories of sleep duration, with control of the confounding variables, and the Wald test was used to assess the significance of the variable in the model. In all statistical analyses, the level of significance probability was set at 5%.

ERICA was approved by the Research Ethics Committee (REC) of each of the 27 participating institutions, one in each unit of the Brazilian federation, and of the institutions that participated in the pilot study. The adolescents signed an informed consent form and, when required by the local REC, brought the free and informed consent form signed by their parents/guardians.

RESULTS

In this study, 65,837 adolescents from the ERICA study population were considered to have complete data on the variables relating to nutritional status (BMI) and hours of sleep. Short sleep duration had a prevalence of 17.9% (95%CI 17 – 18.8) among adolescents, while long duration was observed in 3.6% (95%CI 3 – 4.3) of the sample, with no gender differences (p = 0.146).

The descriptive analyses showed that most of the adolescents who composed the sample were females (56.6%) and aged 15 to 17 years (54.9%). There was also a higher proportion of participants with sedentary behavior when characterized in the final stages of sexual maturation, race/skin color as brown, yellow and indigenous, who were students from public schools in urban areas, who studied in the morning period and whose mothers had more than 8 years of study (Table 1).

The prevalence of overweight in adolescents who reported short sleep duration was 32% of adolescents aged 12 to 14 years, being significantly higher among adolescents in the stage of complete sexual maturation (31.2%), among students from private schools (34.5%) and whose mothers’ education was over 8 years of study (31.3%). Lower prevalence of overweight was reported in adolescents whose sleep duration was greater than 11 hours, for all variables being studied, except stage 5, of sexual maturation (Table 1).

A downwards trend in sleep duration as age advances was observed among the adolescents (Figure 1). The average hours of sleep for the 12-year-old age group was 8.66 ± 1.35 hours for girls and 8.73 ± 1.38 hours for boys. However, at 17 years of age, these averages are 7.81 ± 1.30 and 7.67 ± 1.31 for girls and boys, respectively, with a reduction of almost one hour of sleep per day. Until the age of 14, boys had a longer average sleep duration than girls; however, from the age of 15 on, they begin to show a more pronounced decline.

The most prevalent nutritional disorder among ERICA adolescents was overweight, found in more than 1/4 of the population (25.5%). The prevalence of overweight among adolescents with short sleep duration was significantly higher than among adolescents with long sleep duration, with values of 26.9 (95%CI 25.3 – 28.7) and 20.5% (95CI % 16.9 – 24.7), respectively (Table 2).

We found a higher prevalence ratio for excess weight in the category of short sleep duration when compared with long sleep duration, both in crude and adjusted analyses, as observed in Table 3. When adjusted for potential confounding factors such as age, sexual maturation stage, race/skin color, type and region of the school, both short and long sleep durations remained associated with overweight. Using the sleep duration of 7 to 11 hours a day as a reference for the analyses, we found that adolescents who reported sleeping less than 7 hours have about 10% (PR = 1.10; 95%CI 1.06 – 1.15) more overweight than adolescents with adequate sleep time; however, adolescents who reported sleeping more than 11 hours had about 12% (PR = 0.88; 95%CI 0.78 – 0.99) less excess weight when compared with those who reported adequate sleep time, which suggests that sleep duration in adolescence is an important component in the prevalence of this nutritional disorder.

DISCUSSION

Studies on the association between sleep duration and excess weight in a representative sample of Brazilian children and adolescents are still scarce¹¹11. Halal CS, Matijasevich A, Howe LD, Santos IS, Barros FC, Nunes ML. Short sleep duration in the first years of life and obesity/overweight at age 4 years: a birth cohort study. J Pediatr 2016; 168: 99-103.e3. https://doi.org/10.1016/j.jpeds.2015.09.074
https://doi.org/10.1016/j.jpeds.2015.09.... ^,2222. Schäfer AA, Domingues MR, Dahly DL, Meller FO, Gonçalves H, Wehrmeister FC, et al. Sleep Duration Trajectories and Body Composition in Adolescents: Prospective Birth Cohort Study. Plos One 2016; 11(3): e0152348. https://doi.org/10.1371/journal.pone.0152348
https://doi.org/10.1371/journal.pone.015... . In this sense, the results presented here are of great relevance and will contribute substantially to epidemiological research and to preventive and intervention measures, as being overweight is a relevant health problem that generates physical, emotional and social damage²³23. Enes CC, Slater E. Obesidade na adolescência e seus principais fatores determinantes. Rev Bras Epidemiol 2010; 13(1): 163-71. https://doi.org/10.1590/S1415-790X2010000100015
https://doi.org/10.1590/S1415-790X201000... , often irreparable, with a consequent reduction in the quality of life of a large portion of the affected population²⁴24. Zeller MH, Modi AC. Predictors of health-related quality of life in obese youth. Obesity 2006; 14(1): 122-30. https://doi.org/10.1038/oby.2006.15
https://doi.org/10.1038/oby.2006.15... ^,2525. Al-Akour NA, Khader YS, Khassawnhe MY, Bawadi H. Health-related quality of life of adolescents with overweight or obesity in the north of Jordan. Child Care Health Dev 2012; 38(2): 237-43. https://doi.org/10.1111/j.1365-2214.2011.01248.x
https://doi.org/10.1111/j.1365-2214.2011... .

Our results show a higher prevalence of overweight among adolescents with short sleep duration. This association remained independent even after adjusting the analyses, thus confirming the hypothesis that Brazilian students who maintain a sleep habit of less than 7 hours on a daily basis are more likely to gain weight. Adolescents who reported having short sleep had 10% (PR = 1.10; 95%CI 1.06 – 1.15) more overweight, while those who reported sleeping more than 11 hours had approximately 12% (PR = 0.88; 95%CI 0.78 – 0.99) less excess weight, corroborating other studies of great epidemiological relevance that also pointed the relationship between sleep duration and weight gain in the most diverse ages and in different countries¹¹11. Halal CS, Matijasevich A, Howe LD, Santos IS, Barros FC, Nunes ML. Short sleep duration in the first years of life and obesity/overweight at age 4 years: a birth cohort study. J Pediatr 2016; 168: 99-103.e3. https://doi.org/10.1016/j.jpeds.2015.09.074
https://doi.org/10.1016/j.jpeds.2015.09.... ^,2222. Schäfer AA, Domingues MR, Dahly DL, Meller FO, Gonçalves H, Wehrmeister FC, et al. Sleep Duration Trajectories and Body Composition in Adolescents: Prospective Birth Cohort Study. Plos One 2016; 11(3): e0152348. https://doi.org/10.1371/journal.pone.0152348
https://doi.org/10.1371/journal.pone.015... ^,2626. Mitchell JA, Rodriguez D, Schmitz KH, Audrain-McGovern J. Sleep duration and adolescent obesity. Pediatrics 2013; 131(5): e1428-34. https://dx.doi.org/10.1542%2Fpeds.2012-2368
https://dx.doi.org/10.1542%2Fpeds.2012-2... .

The prevalence of short sleep duration among adolescents was higher (17.9% 95%CI 17 – 18.8), when compared to the habit of sleeping approximately 11 hours daily (3.6% 95%CI 3 – 4.3). A representative study with 11,830 Chinese children ratifies the prevalence found here, using as a cut-off point for short sleep duration less than 7 hours per day²⁷27. Cao M, Zhu Y, He B, Yang W, Chen Y, Ma J, et al. Association between sleep duration and obesity is age- and gender-dependent in Chinese urban children aged 6–18 years: a cross-sectional study. BMC Public Health 2015; 15: 1029. https://dx.doi.org/10.1186%2Fs12889-015-2359-0
https://dx.doi.org/10.1186%2Fs12889-015-... . Sleep duration among Australian, European, American and Asian adolescents was studied by Olds et al.²⁸28. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... , who reported a significant difference in sleep duration between cultures. Young Asians sleep less, and their prevalence for short sleep duration is similar to those found here²⁸28. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... .

Lund et al. state that short sleep duration in adolescence is associated with numerous unfavorable health outcomes, including metabolic and cognitive problems²⁹29. Lund HG, Reider BD, Whiting AB, Prichard JR. Sleep patterns and predictors of disturbed sleep in a large population of college students. J Adolesc Health 2010; 46(2): 124-32. https://doi.org/10.1016/j.jadohealth.2009.06.016
https://doi.org/10.1016/j.jadohealth.200... .

According to recommendations, it is possible that young people need to sleep, on average, 8 hours a night²⁶26. Mitchell JA, Rodriguez D, Schmitz KH, Audrain-McGovern J. Sleep duration and adolescent obesity. Pediatrics 2013; 131(5): e1428-34. https://dx.doi.org/10.1542%2Fpeds.2012-2368
https://dx.doi.org/10.1542%2Fpeds.2012-2... ; however, there is no consensus in the literature regarding the ideal amount of sleep for adolescence, which makes it difficult to compare studies. Our demonstrate that adolescents sleep, on average, 8 hours or more until they are 15 years old. However, as age advance, the averages drop considerably in older students and in the final stages of sexual maturation.

Similar results can be observed in national²²22. Schäfer AA, Domingues MR, Dahly DL, Meller FO, Gonçalves H, Wehrmeister FC, et al. Sleep Duration Trajectories and Body Composition in Adolescents: Prospective Birth Cohort Study. Plos One 2016; 11(3): e0152348. https://doi.org/10.1371/journal.pone.0152348
https://doi.org/10.1371/journal.pone.015... ^,3030. Felden EPG, Filipin D, Barbosa DG, Andrade RD, Meyer C, Louzada FM. Factors associated with short sleep duration in adolescents. Rev Paul Pediatr 2016; 34(1): 64-70. https://doi.org/10.1016/j.rppede.2015.10.007
https://doi.org/10.1016/j.rppede.2015.10... and international²⁷27. Cao M, Zhu Y, He B, Yang W, Chen Y, Ma J, et al. Association between sleep duration and obesity is age- and gender-dependent in Chinese urban children aged 6–18 years: a cross-sectional study. BMC Public Health 2015; 15: 1029. https://dx.doi.org/10.1186%2Fs12889-015-2359-0
https://dx.doi.org/10.1186%2Fs12889-015-... ^,2828. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... studies that report a downwards trend in sleep duration in the course of adolescence explained by maturation factors, in which slower melatonin secretion, especially in the late stages of puberty, leads to a delay in the sleep phase, characterized by later bedtime and waking up³¹31. Carskadon MA, Acebo C, Jenni OG. Regulation of adolescent sleep: implications for behavior. Ann N Y Acad Sci 2004; 1021: 276-91. https://doi.org/10.1196/annals.1308.032
https://doi.org/10.1196/annals.1308.032... . The increase of work activities among older adolescents and the greater availability of computers, televisions and video games in their bedrooms contribute to exacerbating this trend³²32. Owens J, the Adolescent Sleep Working Group, Committee on Adolescence. Insufficient sleep in adolescents and young adults: an update on causes and consequences. Pediatrics 2014: 134(3): e921-32. https://doi.org/10.1542/peds.2014-1696
https://doi.org/10.1542/peds.2014-1696... .

A study suggested that girls sleep more than boys²⁸28. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... , but our results show no significant difference between genders (p = 0.146), despite the tendency for boys to sleep less after the age of 15. This difference may be associated with the phase change induced by testosterone in boys³¹31. Carskadon MA, Acebo C, Jenni OG. Regulation of adolescent sleep: implications for behavior. Ann N Y Acad Sci 2004; 1021: 276-91. https://doi.org/10.1196/annals.1308.032
https://doi.org/10.1196/annals.1308.032... , whose hormonal environment would be leading them to stay awake until later. However, the reasons for general sexual differences in sleep time are not yet clear²⁸28. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... .

Morning shift students had a higher prevalence of short sleep duration (23.5% 95%CI 21.9 – 25.2), compared to afternoon shift students (6.3% 95%CI 5.6 – 7.1), confirming previous findings that state that the time to start classes contributes to short sleep²⁸28. Olds T, Bluden S, Petkov J, Forchino F. The relationships between sex, age, geography and time in bed in adolescents: A meta-analysis of data from 23 countries. Sleep Med Rev 2010; 14(6): 371-8. https://doi.org/10.1016/j.smrv.2009.12.002
https://doi.org/10.1016/j.smrv.2009.12.0... ^,3030. Felden EPG, Filipin D, Barbosa DG, Andrade RD, Meyer C, Louzada FM. Factors associated with short sleep duration in adolescents. Rev Paul Pediatr 2016; 34(1): 64-70. https://doi.org/10.1016/j.rppede.2015.10.007
https://doi.org/10.1016/j.rppede.2015.10... . The delay in sleep onset, added to the commitment to wake up early, conflicts with the biological needs of adolescents, further reducing sleep time³²32. Owens J, the Adolescent Sleep Working Group, Committee on Adolescence. Insufficient sleep in adolescents and young adults: an update on causes and consequences. Pediatrics 2014: 134(3): e921-32. https://doi.org/10.1542/peds.2014-1696
https://doi.org/10.1542/peds.2014-1696... ; for this reason, the American Academy of Pediatrics, in view of the potential benefits for students with regard to physical and mental health, safety and academic performance, recommends that the start time of classes be late³³33. American Academy of Pediatrics. Committee on Public Education. Children, adolescents, and television. Pediatrics 2001; 107(2): 423-6. https://doi.org/10.1542/peds.107.2.423
https://doi.org/10.1542/peds.107.2.423... .

In this study, a higher prevalence of short and long-term sleep among black adolescents can be observed, an end-to-end variation in the usual sleep time. A study with adolescents, in a birth cohort representing racial minorities, evaluated the duration of sleep using actigraphy and observed a shorter sleep duration among African-American participants³⁴34. Javaheri S, Storfer-Isser A, Rosen CL, Redline S. Association of short and long sleep durations with insulin sensitivity in adolescents. J Pediatr 2011; 158(4): 617-23. https://doi.org/10.1016/j.jpeds.2010.09.080
https://doi.org/10.1016/j.jpeds.2010.09.... . Although this relationship is not yet well understood, it is believed to be linked to genetic, biological and psychosocial factors³⁵35. Adenekan B, Pandey S, McKenzie F, Zizi F, Casimir G, Jean-Louis G. Sleep in America: Role of racial/ethnic diferences. Sleep Med Rev 2013; 17(4): 255-62. https://doi.org/10.1016/j.smrv.2012.07.002
https://doi.org/10.1016/j.smrv.2012.07.0... , but there is little evidence about this relationship among adolescents.

Our study consolidates the high prevalence of overweight and obesity in Brazilian adolescents, as recent research accounts for more than ¼ of this population diagnosed with overweight⁴4. Leal MABF, Paiva SSC, Sousa SSL, Lima CEB, Silva ARV, Nascimento FF, et al. Fatores sociodemográficos e comportamentais associados ao excesso de peso em adolescentes brasileiros – 2015. Adolesc Saúde 2019; 16(2): 16-26.^,3636. Schommer VA, Barbiero SM, Cesa CC, Oliveira R, Silva AD, Pellanda LC. Excesso de peso, variáveis antropométricas e pressão arterial em escolares de 10 a 18 Anos. Arq Bras Cardiol 2014; 102(4): 312-8. https://doi.org/10.5935/abc.20140038
https://doi.org/10.5935/abc.20140038... . From the perspective of sleep duration, more than 26% of the population affected by a deficit in sleep duration has this nutritional disorder and a drop of around 6% in the prevalence of excess weight is seen when adolescents have a longer sleep duration, confirming previously published findings¹¹11. Halal CS, Matijasevich A, Howe LD, Santos IS, Barros FC, Nunes ML. Short sleep duration in the first years of life and obesity/overweight at age 4 years: a birth cohort study. J Pediatr 2016; 168: 99-103.e3. https://doi.org/10.1016/j.jpeds.2015.09.074
https://doi.org/10.1016/j.jpeds.2015.09.... ^,2222. Schäfer AA, Domingues MR, Dahly DL, Meller FO, Gonçalves H, Wehrmeister FC, et al. Sleep Duration Trajectories and Body Composition in Adolescents: Prospective Birth Cohort Study. Plos One 2016; 11(3): e0152348. https://doi.org/10.1371/journal.pone.0152348
https://doi.org/10.1371/journal.pone.015... .

The average sleep time duration was associated with changes in the distribution of BMI in a representative sample of adolescents in eight study waves, in which the authors reported little sleep as associated with a higher BMI from 14 to 18 years old. These data support the recommendation that adolescents should sleep between 8.5 and 10.5 hours a day, as it would have a significant impact on preventing overweight²⁶26. Mitchell JA, Rodriguez D, Schmitz KH, Audrain-McGovern J. Sleep duration and adolescent obesity. Pediatrics 2013; 131(5): e1428-34. https://dx.doi.org/10.1542%2Fpeds.2012-2368
https://dx.doi.org/10.1542%2Fpeds.2012-2... .

Among the limitations of this study, the study design should be considered, since ERICA is a cross-sectional study and it prevents analysis of causal relationship. In addition, it should be noted that the sleep duration and physical activity assessments were self-reported by adolescents, which may result in error; however, the self-reported sleep duration is widely and worldwide used and indicated for measuring sleep hours of teenagers³⁷37. Wolfson AR, Carskadon MA, Acebo C, Seifer R, Fallone G, Labyak SE, et al. Evidence for the validity of a sleep habits survey for adolescents. Sleep 2003; 26(2): 213-6. https://doi.org/10.1093/sleep/26.2.213
https://doi.org/10.1093/sleep/26.2.213... . Another important limitation is related to the loss of data due to inconsistencies in responses of the sleep variable, although a careful analysis of the distribution of responses in ERICA has allowed an important percentage to be corrected and used (reduction from 18.67 to 10.64% losses), the final sample remaining representative¹⁹19. Abreu GA, Silva TLN, Teixeira LR, Block KV. Análise da qualidade da informação autorreferida sobre duração do sono de escolares do Estudo de Riscos Cardiovasculares em Adolescentes (ERICA). Cad Saúde Pública 2019; 35(10): e00152918. https://doi.org/10.1590/0102-311x00152918
https://doi.org/10.1590/0102-311x0015291... . In addition, the sleep duration reported after corrections is similar to that found in another study³⁰30. Felden EPG, Filipin D, Barbosa DG, Andrade RD, Meyer C, Louzada FM. Factors associated with short sleep duration in adolescents. Rev Paul Pediatr 2016; 34(1): 64-70. https://doi.org/10.1016/j.rppede.2015.10.007
https://doi.org/10.1016/j.rppede.2015.10... . Finally, the duration of sleep can influence not only the health of individuals, but also the quality of sleep³⁸38. Paiva T, Gaspar T, Matos MG. Sleep deprivation in adolescents: correlations with health complaints and health-related quality of life. Sleep Med 2015; 16(4): 521-7. https://doi.org/10.1016/j.sleep.2014.10.010
https://doi.org/10.1016/j.sleep.2014.10.... , data that were not assessed in the ERICA study.

Based on the results presented here, we conclude that short sleep duration is associated with an increase in the prevalence of overweight among adolescents, adding to the growing body of evidence that supports this relationship. Encouraging children and adolescents to sleep regularly and sufficiently can be a cost-effective intervention for the prevention of excess weight in this age group. Public health policies, with regard to adequate hours of sleep, can be significant for the promotion of health and the prevention of this problem of great relevance to health. Therefore, we encourage the inclusion of the variable sleep duration in the routine of services and in the planning of health actions as a measure to prevent diseases and non-communicable comorbidities.

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