Nutrition, health and schoolchildren : Nutrition, health and schoolchildren

The prevalence and severity of obesity have increased in recent years, likely the result of complex interactions between genes, dietary intake, physical activity, and the environment. The expression of genes favoring the storage of excess calories as fat, which have been selected for over many millennia and are relatively static, has become maladaptive in a rapidly changing environment that minimizes opportunities for energy expenditure and maximizes opportunities for energy intake. The consequences of childhood and adolescent obesity include earlier puberty and menarche in girls, type 2 diabetes and increased incidence of the metabolic syndrome in youth and adults, and obesity in adulthood. These changes are associated with cardiovascular disease as well as with several cancers in adults, likely through insulin resistance and production of inflammatory cytokines. Although concerns have arisen regarding environmental exposures, there have been no formal expert recommendations. Currently, the most important factors underlying the obesity epidemic are the current opportunities for energy intake coupled with limited energy expenditure.

We provide a wide-ranging review of health-related physical activity in children and adolescents using a behavioural epidemiology framework. In contrast to many other reviews, we highlight issues associated with true sedentary behaviours alongside physically active behaviours. Specifically, we review the evidence concerning the links between physical activity and cardiovascular disease, overweight and obesity, psychosocial measures, type II diabetes, and skeletal health. Although the evidence is unconvincing at times, several factors lead to the conclusion that promoting physical activity in youth is desirable. A review of the prevalence of physical activity and sedentary behaviours shows that many young people are active, but this declines with age. A substantial number are not adequately active for health benefits and current trends in juvenile obesity are a cause for concern. Prevalence data on sedentary behaviours are less extensive but suggest that total media use by young people has not changed greatly in recent years. Most children and adolescents do not exceed recommended daily hours of TV viewing. Physical activity is unrelated to TV viewing. We also identified the key determinants of physical activity in this age group, highlighting demographic, biological, psychological, behavioural, social and environmental determinants. Interventions were considered for school, family and community environments. Finally, policy recommendations are offered for the education, governmental, sport and recreation, health, and mass media sectors.