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1 From the Section of Pediatric Endocrinology, Medical Center, University of California, Davis, Sacramento, CA.
See corresponding article on page 308.
Past and incumbent Surgeons General have alluded to an epidemic of overweight children in the United States, and similar trends are found in many other countries. The prevalence of children with a body mass index (BMI) above the 95th percentile for age—defined as overweight when dealing with children and adolescents according to the Centers for Disease Control and Prevention (CDC), in contrast with the term obesity, which is widely used in adults—has increased 100%. The prevalence of children with a BMI above the 85th percentile for age (defined as at risk for overweight in children and adolescents by the CDC) has increased 50%. These increases have occurred mostly during the period between the second (1976–1980) and third (1988–1994) National Health and Nutrition Examination Surveys (1). The CDC notes that as of 1999, the prevalence of overweight has increased further to 13% among 6–11-y-olds and to 14% among 12–19-y-olds. In this issue of the Journal, Caballero et al (2) show that in American Indian children of a mean age of 7.6 y, the prevalence of BMI above the 85th percentile for age is already 48.9% and the prevalence of BMI above the 95th percentile is 28.6%. Although these authors note that this ethnic group is affected more than are others, it is inescapable that the trend toward childhood overweight starts early in life in all groups studied. The problem of childhood overweight, previously over-optimistically viewed as a temporary phase that children would "grow out of," is now well demonstrated to track into adulthood in a large percentage of cases (3).
Childhood overweight precedes adult obesity in 30% of cases, and an adult who was an obese child has a likelihood of more serious comorbidities than if the obesity developed in adulthood. Nonetheless, an overweight child can suffer complications while still in the childhood years (reviewed in reference 4). Furthermore, just as the prevalence of overweight differs among ethnic groups, so does the prevalence of comorbidities in overweight children. Type 2 diabetes, a common comorbidity of adult obesity, was first described in Canadian First Nation children (who are considered ethnically comparable with American Indians) in the mid-1980s (5). In the mid-1990s it became apparent that type 2 diabetes also affects adolescent (or younger) African Americans, Hispanic Americans, and, more recently, Asian Americans in greater percentages than found among white Americans (6,7). Other comorbidities that result from an overweight childhood or adolescence range from orthopedic complications to other metabolic conditions that include insulin resistance, such as ovarian hyperandrogenism (or polycystic ovarian disease). The economic costs of an overweight childhood are not yet as clear as the costs of adult obesity, but a recent publication showed a two- to fivefold increase in overweight-related hospital discharges (depending on the admission condition) in children and a tripling of the economic cost of hospitalization of overweight children from $35 to $127 million during the past 2 decades (8). However, these data do not begin to address the substantial psychosocial effects of overweight in childhood.
The remarkable prevalence of overweight in childhood appears related to environmental and behavior changes in the population, rather than to a change in the genetic makeup of the affected children. For example, there is an alarming decrease in enrollment in gym classes and participation in physical activity by adolescents that is more pronounced in girls than in boys and more pronounced in African American girls than in white girls (9).
What is the answer to the situation? Overweight children are most often treated in clinics by using the medical disease model or in family-centered group programs in which already established habits are targeted for change, if they are treated at all. In some, but certainly not most cases, these interventions are successful. But when we approach a problem that affects close to one-quarter of the population, we surely cannot solve the problem by using the paradigm of the diagnosis and treatment of a disease. Prevention is clearly the most important approach. Changing television-viewing habits was successful in moderating weight in a randomized control trial (10), but there is still a paucity of other proven methods to prevent overweight. Recent newspaper articles note that health departments, overwhelmed by the increased number of children and adults with type 2 diabetes related to overweight, have targeted treatment of complications in the absence of proven methods of prevention of excessive weight gain. Only by developing successful methods of behavior modification related to nutrition and activity that start at a young age can we address the problem. On the positive side, there have been increased requests for proposals from the National Institutes of Health on the subject, and foundations are funding projects addressing this problem. There is a need for more research in numerous areas and for policy change. Whether we have the national will to approach the multitude of political, sociologic, and commercial issues that have brought us to this point remains to be seen. If we do not, we may look back at the start of the 21st century as the good old days when childhood overweight affected no more than 25% of American children.
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