The prevalence of childhood obesity has increased globally over the past three decades, with evidence of recent leveling off in developed countries. Reduction in the, currently high, prevalence of obesity will require a full understanding of the biological and social pathways to obesity in order to develop appropriately targeted prevention strategies in early life. Determinants of childhood obesity include individual level factors, including biological, social, and behavioral risks, acting within the influence of the child's family environment, which is, in turn, imbedded in the context of the community environment. These influences act across childhood, with suggestions of early critical periods of biological and behavioral plasticity. There is evidence of sex and gender differences in the responses of boys and girls to their environments. The evidence that determinants of childhood obesity act at many levels and at different stages of childhood is of policy relevance to those planning early health promotion and primary prevention programs as it suggests the need to address the individual, the family, the physical environment, the social environment, and social policy. The purpose of this narrative review is to summarize current, and emerging, literature in a multilevel, life course framework.
INTRODUCTIONThe prevalence of childhood obesity has increased globally over the past three decades, with more rapid increases recently occurring in low-income countries (1). In the United States, more than 30% of children are now overweight or obese (1), with evidence that the prevalence has leveled off (2). Children and adolescents are exhibiting obesity-related conditions such as type 2 diabetes, elevated blood pressure, low-density lipoprotein cholesterol, and higher fasting insulin levels (3-6). In addition, childhood obesity predicts adulthood obesity and its known health consequences (7,8). Treatment of obesity is notoriously difficult, with weight loss rarely sustained in adults (9). Therapeutic interventions in childhood are somewhat more successful, particularly if the intervention occurs prior to onset of puberty (10). However, real and sustained progress in combating the obesity epidemic will require a full understanding of the biological and social pathways to obesity in order to develop appropriately targeted prevention strategies in early life.Pathways to childhood obesity are complex. It is therefore helpful to discuss determinants of obesity within a conceptual framework. A multilevel conceptual model, Bronfenbrenner's Bioecological Systems Theory (11), has previously been applied to the conceptualization of childhood obesity by Davison and Birch (12). This framework depicts individual-level factors, including biological, social, and behavioral risks, as acting within the influence of the child's family environment, which is, in turn imbedded in the context of the community environment. It is also helpful to consider critical periods for obesity risk and, as will be further illustrated in a later section,...