Secular trends in variables associated with the metabolic syndrome of North American children and adolescents: A review and synthesis

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Abstract
The aim of this article is to summarize and critique reports from selected large-scale population health surveys (U.S. and Canada national health surveys (e.g., National Health and Nutrition Examination Survey, Youth Risk Behavior Survey, and Canada Fitness Survey), and active research programs in preventive pediatric cardiology (i.e., Bogalusa Heart Study, Princeton Lipids Study, and Minneapolis Blood Pressure Study)) pertaining to the secular trend in variables associated with the metabolic syndrome of North American youth. These surveys were chosen since they have published peer-reviewed articles on the topic and consist of relatively large samples. The increased body mass index and prevalence of overweight and obesity are clear, particularly over the past two decades. The secular increase in overweight and obesity cannot be linked to available self-report data on physical activity or diet, although measurement issues need to be considered. The emergence of Type II diabetes in adolescents parallels the increase in obesity; however, subsequent changes in blood lipids and blood pressure are less clear. There is some evidence to suggest adverse changes in the blood lipid profile. Aerobic fitness, as determined by maximal oxygen consumption (VO(2max)), has not appeared to change in youth except perhaps for adolescent females. The results suggesting the emergence of metabolic syndrome X during childhood and adolescence are discussed in the context of perturbation and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. It can be suggested that a subsistent lifestyle consisting of increased lifestyle activity (not exercise per se), a prudent diet, adequate sleep and rest, and stress reduction be advocated to combat diseases of Western Civilization/metabolic syndrome that have affected North American children (and adults) in recent years. The results also highlight the importance of population surveillance of obesity, physical activity, and dietary intake and cardiovascular health of children into the 21st century.