Abstract
Health Consequences of Childhood Obesity
Childhood obesity should no longer be considered a cosmetic problem, but rather should be perceived as a condition that engenders dangerous health consequences. There is no question now that childhood obesity tracks ineluctably into adulthood, bringing with it a predisposition to cardiovascular disease, hypertension and stroke, and a variety of cancers, as well as steatohepatitis, pancreatic beta cell exhaustion, and type 2 diabetes.
Pinhas-Hamiel et al. called attention to a disturbing trend in obese adolescents by documenting a tenfold increase in prevalence of type 2 diabetes, from 0.7 to 7.0 per 100,000 per year in obese adolescents in Cincinnati over a 12-year period of time. 2 Din-Dzietham et al. reported that a decade after the increase in the prevalence of childhood obesity was observed in data from NHANES I, the gratifying downward trend in childhood blood pressure from 1963 to 1988 suddenly reversed itself, with significant increases in blood pressure and pre-hypertension in children of all races and ethnicities, although non-Hispanic black and Mexican American children had greater prevalence of hypertension and pre-hypertension than non-Hispanic white children. 3
Non-alcoholic steatohepatitis (NASH) is the most prevalent liver disease among U.S. children between ages 10 and 18 years, affecting about 38% of obese adolescents. 4 NASH is, arguably, the most serious early side effect of childhood obesity, occurring in obese children at the time of puberty. In severe cases, NASH leads to hepatic fibrosis, cirrhosis, and, ultimately, liver failure curable only by liver transplantation. Also worrisome is the recognition that cardiovascular risk and morbidity in children and adolescents are associated with NASH. Little is known of NASH's pathogenesis or treatment, although Burgert et al. and Cali et al. showed that NASH in adolescents is strongly associated with the triad of insulin resistance, increased visceral fat, and low levels of serum adiponectin.5,6
Sun et al. performed a retrospective analysis of childhood data from the Fels Longitudinal Study and reported that children with a mean waist circumference of 65 cm at age 9 years were significantly more likely to develop the metabolic syndrome as adults than children with waist circumferences of 60 cm at age 9 years. 7 Presumably waist circumference serves as a proxy for accumulation of metabolically active visceral fat. This demonstration of the power of an increased waist circumference in childhood to predict the onset of the metabolic syndrome decades later in the same individual again indicates the manifold threats to health engendered by childhood obesity.
Causes of the Epidemic
A perfect storm of decreased physical activity, augmented amounts of food intake, and increased availability of inexpensive food of high-caloric density has combined to generate the epidemic of childhood obesity that we have witnessed over the past three decades. Social factors also contribute to the development of obesity. For example, Christakis and Fowler, in a groundbreaking study of the Framingham population, showed the importance of social networks in the transmission of obesity by revealing the power exerted by friendships in generating weight gain or weight-related behaviors that are accepted, or even promoted, by the parties involved. 8 Salvy, Kieffer, and Epstein performed similar work in children, showing that overweight children were more likely to choose a healthy snack if a person eating with them selected a healthy snack. 9
Caloric intake has greatly increased over the past three decades, a phenomenon that has contributed to our current prevalent energy imbalance. Wang and Beydoun reviewed several analyses of dietary intake data from 1977 through 1996 that revealed a trend toward greater portion sizes in the United States, resulting in higher caloric intakes of between 50 and 150 kcal per item for commonly consumed food items, such as hamburgers, French fries, and Mexican food. 10 Young and Nestle reported that portion sizes of French fries, hamburgers, and soft drinks have doubled, tripled, or even quintupled in tandem with the epidemic of childhood obesity. 11 These authors noted that portion sizes began to grow in the 1970s, rose sharply in the 1980s, and have continued in parallel with increasing body weights.
Hours of television viewing are also strongly associated with an increased risk of obesity in childhood and adolescence owing to several associated factors, such as inactivity, exposure to thousands of advertisements per year for snack food of high caloric density and low nutritional value, and frequent snacking. Robinson reported that children spend about one-third of their waking hours in front of television screens, and Roberts et al. found that children from racial and ethnic minority groups spend even more time watching television.12,13 Gortmaker et al. estimated that as much as 60% of the incidence of overweight could be linked to excess television viewing. 14 These authors reported that the adjusted odds of being overweight were more than eight times greater for children who watched more than 5 hours of television per day compared with those watching for 2 hours or less. They concluded that reducing television-viewing time could help prevent this increasingly common chronic health condition.
Because obesity in childhood is associated with hypertension, Pardee et al. studied the interaction of these two factors in more than 500 children and adolescents. 15 These investigators reported that both the severity of obesity and daily television-watching time were significant independent predictors of pediatric hypertension and that the amount of time spent watching television was associated with both hypertension and the severity of obesity. The odds of hypertension for children watching 4 or more hours of television per day were more than three times greater than for children watching less than 2 hours of television per day. Thus, limiting television-watching time is a potential partial solution for reversing the twin epidemics of obesity and hypertension in our children.
Policy Issues
The urge to utilize tax policies to ameliorate the epidemic of childhood obesity began when Felix Ortiz introduced a bill in the New York State Assembly to tax items that contribute to the obesity epidemic, including junk food, videogames, and television, thus prompting a New York City teenager to comment wryly, “That's pretty much everything I do.” 16 Another New Yorker, Thomas Frieden, then New York City commissioner of health, now director of the Centers for Disease Control and Prevention, recently advocated a one-cent-per-ounce tax on sugared beverages, a tax that would engender an estimated 13% reduction in nationwide consumption of soft drinks. 17 This is one example of school, food, zoning, and agricultural policies that might be changed in order to ameliorate the epidemic of childhood obesity.
A Systems-Oriented Multilevel Framework for Obesity Research
To date, our interventions have failed to reverse the rising prevalence of pediatric obesity in all races and ethnic groups. This failure may be ascribed to our Cartesian penchant for experimenting with one variable at a time. But childhood obesity is a product of a modern lifestyle characterized by labor-saving devices and the availability of inexpensive food of high caloric density with multiple contributory social and economic factors acting simultaneously. To make a stronger impact on the prevalence of childhood obesity, research needs to address the broader system in which children learn, play, and live. Such a systems-oriented framework links genetic and biological factors with socioenvironmental and policy issues that influence children's diet and physical activity.
During the last 3 years, the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (NIH) energized the field of childhood obesity research by emphasizing the need for a systems-oriented multilevel approach, and by developing concrete strategies for implementing new ideas and findings. In 2007, with co-sponsorship from multiple NIH institutes, centers, and offices; the Centers for Disease Control and Prevention (CDC); and the Canadian Institutes of Health Research, the NICHD hosted an international conference to begin developing a coherent multilevel research agenda. The conference, entitled “Beyond Individual Behavior: Multidimensional Research in Obesity Linking Biology to Society,” included three modules: the state of the science on cross-level topics, multilevel interventions, and statistical and computational methodologies for the design and analysis of multilevel studies. The conference brought together experts from a wide range of fields and included an industry panel with representatives from major transnational companies as a way to begin a dialogue on public-private partnerships, which remains an ongoing initiative. The conference generated ideas for how to implement the systems-oriented multilevel framework to address childhood obesity. 18
Research funded by the NIH has demonstrated the importance of the physical, social, and economic environments on childhood obesity. For example, data from the National Longitudinal Study on Adolescent Health show that neighborhoods may affect adolescents' health behavior, diet, and exercise. Urban neighborhoods inhabited by residents with lower socioeconomic status offer few safe venues for outdoor play, a shortcoming that is associated with a higher prevalence of adolescent obesity. Other research shows that access to healthy foods is important. Areas with a high density of fast-food outlets and convenience stores relative to full-service grocery stores are associated with a higher prevalence of childhood obesity. Economic factors such as food marketing and pricing are critical because of their influence on the purchase and consumption of low- versus high-calorie foods.
New Initiatives
To accelerate research progress and translate research findings into effective solutions at the societal level, the NICHD, in partnership with other NIH institutes and offices, the CDC, and the Robert Wood Johnson Foundation (RWJF), launched the National Collaborative of Childhood Obesity Research (NCCOR) in 2009. The list of NCCOR sponsors was expanded recently by the addition of the U.S. Department of Agriculture. The NCCOR is designed to coordinate and synergize the funding efforts from member organizations and to pool resources for large, ambitious projects that bring us closer to effective and sustainable solutions for the childhood obesity epidemic. For example, NCCOR recently inaugurated Envision, a project that enlists sophisticated computational modeling to elucidate the complexity of the origins of childhood obesity. Investigators within Envision are also testing virtual environmental and policy interventions in model systems to see how such interventions would affect the epidemic of childhood obesity.
The NCCOR will soon begin funding a nationwide study to determine the effectiveness of existing community-based strategies and programs by using a common evaluation approach.
In addition, the National Heart, Lung and Blood Institute (NHLBI) and the NICHD have just launched a new consortium of six clinical centers that will work together to develop creative and novel intervention strategies to prevent and treat pediatric obesity. The consortium will support randomized trials of innovative interventions to prevent excess weight gain in non-overweight youth and in those already overweight, and/or to reduce weight in obese and severely obese youth. The program targets preschool children, pre-adolescents, and adolescents and will promote collaboration, coordination, and exchange of scientific information among institutions and agencies with similar interests. The ultimate goal is to improve children's health by preventing obesity-related conditions later in life.
Other important NIH research initiatives, supported by the National Cancer Institute (NCI); the NHLBI; the NICHD; the National Institute of Diabetes, Digestive and Kidney Diseases (NIDDK); the Office of Behavioral and Social Sciences Research; and the National Institute of Nursing Research, along with the CDC, the U.S. Department of Agriculture, and the RWJF, include recent program announcements on encouraging community-based partnerships of obesity researchers and local or state-level policy makers, and research on school and community policies that impact obesity-related behaviors and outcomes. Because health is a product of more than individual behaviors, through the NCCOR partnership, the NIH is rapidly expanding its research programs on the causes, prevention, and treatment of childhood obesity that should have a large and long-lasting impact at the population level. For additional information, visit www.nccor.org.
The NIDDK maintains a strong clinical research presence in the area of pediatric obesity. NIDDK's Pediatric Clinical Obesity Program emphasizes clinical research relating to biomedical and behavioral aspects of obesity in children and adolescents, including the impact of the fetal and neonatal environments on pediatric obesity. The program encompasses clinical studies investigating appetite and food intake; energy expenditure; body composition; the long-term impact of obesity or its treatment, such as bariatric surgery, on body composition; metabolic factors; psychosocial factors; and comorbid conditions.
The National Longitudinal Study of Children and Their Environment (aka The National Children's Study, or NCS) is led by the NICHD, and is a consortium of federal partners: the U.S. Department of Health and Human Services (including the NICHD), the National Institute of Environmental Health Sciences of the NIH, the CDC, and the U.S. Environmental Protection Agency. The NCS will study 100,000 American children from before birth to 21 years of age to determine what genetic and environmental factors contribute to the development of several chronic diseases and conditions. Childhood obesity is a lead focus of the NCS, and the study will take a life course approach to the epidemiology of obesity by considering the origin of obesity from preconception through late adolescence and will look at genetic inheritance; individual behaviors; the social, built, and natural environments; as well as chemical exposures. For additional information, see www.nationalchildrensstudy.gov.
Outreach Programs
The NICHD is implementing an after-school program, known as Media Smart Youth, for young adolescents to teach them about the complex media and marketing choices they face every day, and how media and food marketing can affect their health, especially by encouraging certain choices in the areas of nutrition and physical activity. Media Smart Youth teaches young people to become critical thinkers; to analyze and evaluate the media messages with which they are bombarded every day, including personalized digital marketing on their own cell phones; and to create their own messages that encourage smart and positive choices. This innovative program is part of the Ways to Enhance Children's Activity and Nutrition (We Can!) program, a collaboration of four NIH institutes (NHLBI, NIDDK, NICHD, and NCI) that offers science-based educational and training tools to promote improved food choices, increased physical activity, and reduced television, computer and videogame screen time for children and families at nearly 1,200 sites across the United States and 11 other countries. For more information, see http://wecan.nhlbi.nih.gov.
We Can! is one of five obesity prevention programs of the DHHS Childhood Overweight and Obesity Prevention Initiative, which was inaugurated in 2007 and is managed by the Surgeon General's Office. The other prevention programs within this obesity prevention initiative include CDC's School Health Index: A Self-Assessment and Planning Guide; the Indian Health Service's Diabetes Prevention Program; the FDA's Using the Nutrition Facts Label to Make Healthy Food Choices; and the President's Council on Physical Fitness and Sports' National Fitness Challenge.
The National Council of Negro Women (NCNW) has joined forces with the NIH to develop and implement a Child Obesity Prevention program, Fit for Life. This program has been developed for African American children and their families, as the epidemic of overweight and obesity disproportionately affects African American children. In an effort to reduce the trend of increasing weight gain in children and adults, NCNW members from 44 states have offered the Fit for Life curriculum to hundreds of children and families. The community-based components of the program include media outreach, partnership development with other national partners, and resources for family members across the life span.
Conclusion
The childhood obesity epidemic is linked not only to children's and parents' behavior, but also, more importantly, to social and economic development and policy areas outside the traditional public health sphere. Thus, we need to deal with obesity as a systems issue, and not simply a health issue. We need to invest resources in research that is multilevel and cross-disciplinary, and we need to include as partners all sectors of our society in order to generate effective and sustainable solutions. The solution to reversing the childhood obesity epidemic will require a coordinated, multisectoral strategy that includes strong actions by all agencies of the U.S. government, state governments, nongovernmental organizations, policy makers at all levels, the food industry, local communities, and especially families.