International trends in 'bottom-end' inequality in adolescent physical activity and nutrition: HBSC study 2002-2014.

Background: In spite of many positive trends that have emerged in the health of young people, adolescents from more affluent groups continue to experience more favourable health outcomes. There are no groups that are more vulnerable than those who report very poor ('bottom-end') indicators of health behaviour. The present study investigated the role of socio-economic factors as potential determinants of bottom-end health behaviours pertaining to physical activity and diet.

Methods: Our analysis incorporated health data for some 700 000 15-year-old adolescents in 34 countries. The data source was four cycles of the Health Behaviour in School-aged Children (HBSC) study (2001/2002, 2005/2006, 2009/2010 and 2013/2014). As per UNICEF precedents, adolescents whose health behaviour scores were below the mean of the lower half of the distribution fell into the 'bottom-end' on this indicator.

Results: Adolescents from less affluent families were much more likely to report being in the bottom-end of the distribution of these health indicators. Large, persistent and widespread socio-economic gradients existed for physical activity and healthy eating, while the findings were mixed for unhealthy eating. Such socio-economic inequalities were largely stable or widened for physical activity and healthy eating, while inequalities in unhealthy eating narrowed.

Conclusion: Although it is important to continue monitoring average levels of adolescent health, national and international policies need to pay attention to the concentration of poor health outcomes among adolescents from less affluent families and to redress social inequalities in adolescent health behaviour.