title: Changes in physical activity and screen time related to psychological well-being in early adolescence: findings from longitudinal study ELANA.
abstract: Psychological well-being influences health behaviours differently in adolescent boys and girls. We evaluated the role of psychological well-being in early adolescence in the onset and persistence of insufficient physical activity and exceeding recommended screen time, depending on gender.
  
  
  
  This work derives from a cohort study called Longitudinal Study of Adolescent Nutritional Assessment conducted among elementary school students from two public and four private schools in Rio de Janeiro, Brazil from 2010-2013. We analysed data from 2010 and 2012 from 526 adolescents. Physical activity was evaluated using the International Physical Activity Questionnaire. Those who performed less than 60 min per day of moderate to vigorous physical activity (MVPA) were classified as insufficiently active. Screen time was evaluated based on daily time spent in front of television, video games, and computers. Those who had 4 h or more screen time per day were classified as exceeding the recommended time. Psychological well-being was assessed using the psychological domain of the KIDSCREEN 27 questionnaire. Linear regression was used to estimate coefficient (β) and r (2) values for continuous variables. Relative risks (RR) and confidence intervals (95 % CI) for onset and persistence of insufficient activity and exceeding recommended screen time were estimated with Poisson regression models.
  
  
  
  Among girls, linear regression analyses showed a significant inverse association between psychological well-being and screen minutes per day at T2 (r (2) = 0.049/β = -3.81 (95 % CI -7.0, -0.9)), as well as an association between poor psychological well-being and onset of exceeding recommended screen time in categorical analyses (RR crude: 1.3; CI 95 % 1.1, 1.7; RR adjusted: 1.3; CI 95 % 1.0, 1.6). For boys, an association was found between psychological well-being and onset of insufficient activity 2 years later (RR crude: 1.3; CI 95 % 1.2, 1.4; RR adjusted: 1.2; CI 95 % 1.1, 1.4).
  
  
  
  Adolescence is crucial for the development of unhealthy behaviours related to psychological well-being status in the context of a middle-income country. Gender differences are important because poor psychological well-being seems to affect sedentary behaviour in girls more than in boys, and predicts insufficient activity among boys.
authors.affiliation: Department of Epidemiology, State University of Rio de Janeiro (UERJ), Rio de Janeiro, Brazil. vica_s@hotmail.com.
authors.forename: Viviane S
authors.initials: VS
authors.lastname: Straatmann
authors.affiliation: Laboratory of Social Dimensions Applied to Physical Activity and Sport (LABSAFE), UFRRJ, Seropédica, Brazil.
authors.forename: Aldair J
authors.initials: AJ
authors.lastname: Oliveira
authors.affiliation: Center for Health and Equity Studies (CHESS), Stockholm, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Rostila
authors.affiliation: Department of Epidemiology, State University of Rio de Janeiro (UERJ), Rio de Janeiro, Brazil.
authors.forename: Claudia S
authors.initials: CS
authors.lastname: Lopes
mesh_terms: D000293:Adolescent; D001938:Brazil; D003201:Computers / Q000706:statistics & numerical data*; D015444:Exercise / Q000523:psychology*; D005260:Female; D015438:Health Behavior; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D012306:Risk; D012574:Schools; D057185:Sedentary Behavior; D012737:Sex Factors; D013334:Students / Q000523:psychology / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires; D013690:Television / Q000706:statistics & numerical data*; D013997:Time Factors; D018910:Video Games / Q000706:statistics & numerical data*
keywords: Adolescents; Longitudinal study; Physical activity; Psychological well- being; Screen time