Sleep and body mass index in adolescence: results from a large population-based study of Norwegian adolescents aged 16 to 19 years

BMC Pediatrics Sleep and body mass index in adolescence: results from a large population-based study of Norwegian adolescents aged 16 to 19 years Brge Sivertsen 0 1 Stle Pallesen Liv Sand Mari Hysing 0 Uni Health, Uni Research Bergen , P.O. Box 7810, Bergen N-5020 , Norway 1 Division of Mental Health, Norwegian Institute of Public Health , Kalfarveien 31, Bergen 5018 , Norway Background: The aim of this study was to examine the association between body mass index (BMI) and sleep duration, insomnia and symptoms of obstructive sleep apnea (OSA) in adolescents. Methods: Data were taken from a large population based study of 9,875 Norwegian adolescents aged 16-19. BMI was calculated from the self-reported body weight and categorized according to recommended age and gender specific cut offs for underweight, overweight and obesity. Detailed sleep parameters (sleep duration, insomnia, and OSA symptoms) were reported separately for weekdays and weekends. Data were analyzed using Pearson's chi-squared test and ANOVAs for simple categorical and continuous comparisons, and multinomial logistic regressions for analyses adjusting for known confounders. Results: There was evidence for a curvilinear relationship between BMI and both sleep duration and insomnia for girls, whereas the relationship was linear for boys. Compared to the average weekday sleep duration among adolescents in the normal weight range (6 hrs 29 min), both underweight (5 hrs 48 min), overweight (6 hrs 13 min) and obese (5 hrs 57 min) adolescents had shorter sleep duration. OSA symptoms were linearly associated with BMI. Controlling for demographical factors as well as physical activity did not attenuate the associations. Additional adjustment for depression reduced the association between insomnia and obesity to a non-significant level. The evidence for a link between both underweight and overweight/obesity, and short sleep duration and OSA symptoms remained in the fully adjusted analyses. The associations were generally stronger for girls. Conclusions: This is one of the first population-based studies to investigate the relationship between sleep and BMI in adolescents while simultaneously controlling for important confounding factors. These findings require further research to investigate the temporal association between weights and sleep problems. Body mass index; Obesity; Overweight; Underweight; Sleep; Sleep duration; Insomnia; Adolescence; Epidemiology - Background Both sleep problems and obesity in adolescence are growing public health concerns. The prevalence of obesity among adolescents in the US population has increased more than 3-fold over the past four decades (from 5% to 18%) [1,2]. Parallel to this epidemic of obesity, which has enormous health and economic consequences [3], there has been a similar decrease in the amount of time spent sleeping. US surveys have shown a decline in self-reported sleep duration over the past 50 years by 1.5 to 2 hours [4], and a similar decrease has been observed among adolescents [5], although the findings in children are mixed [6]. The prevalence of insomnia symptoms has shown a parallel increase in Norwegian adolescents over the last two decades [7]. Several studies have investigated the association between sleep and obesity across different age cohorts, primarily with sleep duration as the variable of interest. In a meta-analysis from 2008 covering 11 studies on children aged 220 years, seven of 11 studies reported a significant association between short sleep duration and obesity [8]. Four longitudinal studies have also examined this link, but the results were inconsistent regarding short sleep duration as an independent risk factor for later obesity among adolescents [9-12]. In a more recent meta-analysis [13], reviewing 15 studies on adolescents (1019 years) investigating the effect of short sleep duration on overweight and obesity, it was concluded that the current evidence was inconclusive as to whether sleep duration was related to adolescent overweight, mainly due to methodological concerns. In addition to the link between obesity and sleep duration, there is ample evidence for obesity as a risk factor for sleep disordered breathing in clinical samples [14]. So far, insomnia (difficulty initiating and maintaining sleep) has received very little attention in relation to body mass index (BMI) in the literature, but has been associated with BMI in young females [15]. Extending on these methodological limitations, the authors of the aforementioned meta-analysis [13] emphasized the following recommendations for future research; 1) to use multiple, detailed and validated measures of sleep; 2) investigate if gender interacts with sleep duration and obesity; 3) adjust for the confounding effects of depression and physical activity; 4) provide separate analyses for both weekday and weekends; and 5) use a prospective design. Against this background, addressing first four of the five recommendations by Guidolin and Gradisar [13], the aims of the current study were: 1) to examine the relationship between multiple and detailed sleep parameters (including sleep duration, insomnia and symptoms of obstructive sleep apnea (OSA)) and body mass index (BMI) in a large population-based sample of 16 to 19year-old adolescents; 2) to investigate girls and boys separately and to examine potential gender differences in the associations between sleep and BMI; 3) to adjust for potential confounding factors, including physical activity and depression; and 4) to provide separate analyses for weekdays and weekends, due to the large observed differences in sleep duration on weekend nights versus school nights [16]. Methods In this population-based study, we used data from the youth@hordaland survey of adolescents in the county of Hordaland in Western Norway. The youth@hordaland survey is the fourth wave of the Bergen Child study, where children born 19931995 are followed from elementary to upper secondary school age. All adolescents and students attending secondary education during spring 2012 were invited to participate. The main aim of the survey was to assess the prevalence of mental health problems and service use in adolescents. Data were collected during spring 2012. Adolescents in upper secondary education received information via their official school e-mail address, and one classroom school hour was allocated for them to complete the questionnaire. The questionnaire was web-based and covered a broad range of mental health issues, daily life functioning, use of health care and social services, demographics, as well as a request for permission to obtain school data, and to link the information with national health registries. Uni Health collaborated with Hordaland County Council to conduct the study. The study was approved by The Regional Committee for Medical and Health Research Ethics in Western Norway. After complete description of the study to the subjects, written (...truncated)