Pediatrics

Sleep Duration and Adiposity During Adolescence

Joana Araújo, Milton Severo and Elisabete Ramos

Pediatrics 2012;130;e1146; originally published online October 1, 2012; DOI: 10.1542/peds.2011-1116

The online version of this article, along with updated information and services, is located on the World Wide Web at: http://pediatrics.aappublications.org/content/130/5/e1146.full.html

PEDIATRICS is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1948. PEDIATRICS is owned, published, and trademarked by the American Academy of Pediatrics, 141 Northwest Point Boulevard, Elk Grove Village, Illinois, 60007. Copyright © 2012 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275.

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Sleep Duration and Adiposity During Adolescence

WHAT’S KNOWN ON THIS SUBJECT: Some epidemiologic evidence suggests an inverse association between sleep duration and obesity in various age groups. However, in the case of adolescents, inconsistent results have been reported, which can be partly explained by methodologic options.

WHAT THIS STUDY ADDS: Our study supports an effect of sleep duration in adiposity during adolescence and found gender differences in this association. The results are consistent by using either the traditional longitudinal approach or cross-lagged modeling.

abstract

BACKGROUND AND OBJECTIVE: The association between sleep and obesity has been described in different age groups. However, there are not sufficient data to clarify the inconsistent results reported in adolescents. Our objective was to study the associations between sleep duration and adiposity at 13 and at 17 years of age, with both cross-sectional and longitudinal approaches.

METHODS: We evaluated, as part of an urban population-based cohort (EPITeen), 1171 adolescents at both 13 and 17 years of age. Sleep duration was estimated by self-reported bedtimes and wake-up times. Age- and gender-specific BMI z scores were calculated based on Centers for Disease Control and Prevention references. Body fat percentage (BF%) was assessed by bioelectrical impedance. Regression coefficients (b) and respective 95% confidence intervals (CIs) were used to estimate the association between sleep and BMI z scores and BF%. Additionally, a cross-lagged analysis was performed to investigate the causal relations.

RESULTS: In the cross-sectional analysis, at 13 years, sleep duration was inversely associated with BMI z score only in boys (b = 2 0.155, 95% CI: 20.267 to 20.043); at 17 years, a positive association was found among girls but was only significant for BF% (b = 0.510, 95% CI: 0.061–0.958). In the longitudinal approach, sleep duration at age 13 was inversely associated with BMI z score (b = 20.123, 95% CI: 20.233 to 20.012) and BF% (b = 20.731, 95% CI: 21.380 to 20.081) at 17 years only in boys. These significant associations disappeared after adjustment for adiposity at 13 years. These results were corroborated by those from cross-lagged analysis.

CONCLUSIONS: Our results showed an effect of sleep duration in ad- iposity at younger ages of adolescence and suggested gender differ- ences in this association. Pediatrics 2012;130:e1146–e1154

AUTHORS: Joana Araújo, MPH, Milton Severo, MSC, PhD, and Elisabete Ramos, MPH, PhD

Department of Clinical Epidemiology, Predictive Medicine and Public Health, and Cardiovascular Research & Development Unity, University of Porto Medical School, Porto, Portugal; and Institute of Public Health, University of Porto, Porto, Portugal

KEY WORDS

sleep, BMI, body fat, obesity, longitudinal, adolescence

ABBREVIATIONS

BF%—body fat percentage

CI—confidence interval

FFQ—food frequency questionnaire

KIDMED—Mediterranean Diet Quality Index for children and ado- lescents

Ms Araújo drafted the first version of the manuscript, performed statistical analyses, and contributed to the interpretation of the results; Mr Severo performed statistical analyses and contributed to the interpretation of the results; and Dr Ramos conceived and designed the study and contributed to the interpretation and discussion of the data.

www.pediatrics.org/cgi/doi/10.1542/peds.2011-1116 doi:10.1542/peds.2011-1116

Accepted for publication Jul 3, 2012

Address correspondence to Joana Araújo, MPH, Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Alameda Prof. Hernâni Monteiro 4200-319 Porto, Portugal. E-mail: jfaraujo@med.up.pt

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275). Copyright © 2012 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

FUNDING: Supported by Fundação para a Ciência e a Tecnologia (grants POCTI/SAU-ESP/62399/2004, PTDC/SAU-EPI/115254/2009, and SFRH/BD/78153/2011).

e1146 ARAÚJO et al

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ARTICLE

Overweight is a major public health issue with high prevalence in both adulthood and childhood1–4 and nega- tive health consequences in children and adolescents5,6 and in adulthood.5,7 Apart from direct health conse- quences, overweight also has social and economic repercussions.

From the standpoint of public health, modifiable risk factors, such as envi- ronmental and behavioral factors, are those most promising in terms of pre- vention and control of the obesity epi- demic. Therefore, several studies have focused their research on the role of food intake and physical activity in overweight. However, in recent years, the role of other factors, such as sleep duration, has gained attention.8,9 Sleep deprivation could influence the energy balance and consequently weight gain through various pathways, such as in- terfering in the regulation mechanisms of leptin, ghrelin, cortisol, and glucose or promoting patterns of behavior that cause weight gain (eating behavior and physical inactivity).10

In children, a consistent association was found between short sleep dura- tion and increased risk of obesity.11,12 In adolescents, fewer studies are avail- able,13–17 and their results are not as consistent as in younger children. Al- though some of them found an inverse association,15,16,18 others, which used nationally representative surveys, re- ported inconsistent associations.13,17,19 The reasons for these differences among studies have not been clarified, making it necessary to produce new data that help us to understand the relation between sleep duration and weight gain in adolescents.

The importance of the effect of short sleep duration on weight gain has gained attention because there is evidence that sleep duration appears to have declined in recent decades.20 The analysis of 3 birth cohorts (1974, 1979, and 1986) from Switzerland showed a decreasing

PEDIATRICS Volume 130, Number 5, November 2012

trend of the mean total sleep duration across cohorts due to progressively later bedtime and unchanged wake-up time across decades.20

Adolescence is also characterized by great changes in body composition21 that may not be detectable by BMI. Thus, if we intend to understand the effect of sleep on adiposity, other parameters such as body fat need to be examined. We therefore aimed to study the associations between sleep dura- tion and adiposity (BMI and body fat) during adolescence by using both a cross-sectional and longitudinal ap- proach.

METHODS

Participants

The study population consisted of urban adolescents, members of the EPITeen cohort. As previously reported,22 ado- lescents born in 1990 and enrolled at public and private schools in Porto during 2003–2004 were invited to par- ticipate. The evaluation included self- administered questionnaires and a physical examination, performed by a trained team.

The second evaluation took place in the 2007–2008 school year, and adoles- cents were evaluated by using the same procedures.

At baseline, 2160 adolescents agreed to participate (77.5% of participation rate). Among these, 1716 (79.4%) par- ticipated in the second evaluation of the cohort. Of the 1716 participants reevaluated, we excluded those par- ticipants who did not have complete information in both evaluations re- garding weight or height (n = 95), body fat percentage (BF%; n = 10), and sleep duration (n = 197). We also excluded those with missing values in potential confounders: parental education (n = 3), age at menarche (n = 9), and diet (n = 231), resulting in a final sample of 1171 participants.

We compared the 1171 participants included in this analysis with those not included (considering exclusions and losses of follow-up). Those not included tended to be more frequently from public schools (82.3% vs 71.4%, P , .001) and had less educated parents (parental education ,6 years: 37.3% vs 19.8%). No significant differences were found according to gender and BMI at baseline.

Variables

Participants were asked to report usual bedtimes and wake-up times on week- days. Sleep duration was estimated by the difference between self-reported bedtimes and wake-up times.

Parental education level was measured as the number of successfully com- pleted years of formal schooling, and a new variable was created considering the information of the parent with the higher education level. The variable was used as continuous.

The questions used

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