Special Feature
Childhood Obesity: Causes, Consequences, and Prevention
By Walter R. Anyan, Jr. MD, FAAP
There is nearly universal agreement that obesity is dramatically increasing worldwide in both adults and children, and that the escalation of obesity in the United States should be an important issue for physicians who care for children. It has been stated that if the current rates of increase in obesity in the United States continue, 100% of the American population will be obese by the year 2020!1 A definition of obesity used by the World Health Organization is the Body Mass Index (BMI; the weight in kg divided by the height in meters squared). This criterion for obesity is not age-dependent and so can also be used for children and adolescents. Incidentally, readers who want the best current reference on BMI in childhood and adolescence will find it in Rosner.2 Overweight is defined as BMI 25-30 kg/m2; obesity is defined as BMI greater than 30 kg/m2. Obesity can also be assessed by measuring the subscapular and iliac skinfolds as an index of trunk fat. BMI provides a useful way of comparing weight with height; the skinfold measurements provide information about subcutaneous adipose tissue mass.
Contrary to what many people believe, childhood obesity is almost never a result of an underlying genetic disorder (Prader-Willi, etc.) or a consequence of CNS or hypothalamic damage. One nearly consistent association with obesity is obesity in the family. There is a strong association between obesity at the time of puberty and obesity in adult life. Another underlying association is the tendency for obese children to be more sedentary than their nonobese peers.3 Exercise programs have become an important part of strategies to both prevent and treat childhood obesity.4
The relationship between television watching and childhood obesity has been the subject of a number of comments.5,6 TV viewing can be a risk factor for development of obesity by establishing a "vicious circle": TV viewing produces a sedentary lifestyle, sedentary children watch more television, and television exposes children to advertisements for food products that in themselves are generally fattening.7
Andersen and associates studied 4063 American children 8-16 years of age who were examined as part of the National Health and Nutrition Examination Survey III (NHANES III) between 1988 and 1994. Data were analyzed relating self-estimates of television watching and vigorous physical exercise with indices of obesity.8 Although Andersen et al do not present data that quantify food intake, their article does compare self-reported "exercise that made them sweat or breathe hard three or more times per week" as well as hours of television watched daily with body mass index (BMI) and skinfold (subscapular and suprailiac) thicknesses on the trunk.
In terms of any association with BMI or skinfold thickness in the children studied, hours of daily television watching—or lack thereof—seemed to have more clout than the reported bursts of vigorous physical activity. Eighty percent of subjects recalled meeting the exercise quota. Recall of television watching, an exquisite measurement of inactivity, revealed that while 39% of subjects watched television one hour or less daily, 35% viewed 2-3 hours/day and 26% stayed by their sets four or more hours daily! Vigorous activity levels were lowest in girls, non-Hispanic blacks, and Mexican Americans.
Several findings are particularly interesting. BMI and skinfold thickness were significantly greater in boys who watched more than two hours of television daily and in girls who watched four or more hours daily. However, among boys, BMI also was greater in those reporting 6-8 episodes of vigorous activity per week. When the interaction of vigorous activity and television watching is examined, it appears that the lowest BMI and lowest skinfold measurements were found in boys who had the lowest frequency of vigorous activity (3 or fewer times per week) and the lowest amount of television watching (< 2 hours per day). While the highest BMI was found in those who had the greatest vigorous activity and 2-3 hours of television each day, the boys with the largest skinfold thicknesses had the lowest vigorous activity and the largest amount of television watching. The finding that the group of girls who had the lowest BMI did the least television watching and had 4-5 episodes of vigorous activity per week is similar to the finding in boys, the girls with the highest skinfold measures were those with moderate amounts of vigorous activity and the highest amount of television watching. Interestingly, no subgroup of girls had particularly low skinfold measurements.
Contrary to popular belief, children and adolescents find things to do instead of watching television, and it seems that whatever they do when they don’t watch television is apt to be helpful in restraining the progressive increases of BMI and skinfold thickness that occur during this part of their lives. We continue to have every reason to believe that it is far easier to prevent obesity than to treat it. For the pediatrician, the question, "So, how much television do you watch?," may be one worth asking. We should also strongly endorse the objectives of the International Consensus Conference on Physical Activity Guidelines for Adolescents that "adolescents engage in three or more sessions per week of activities that last 20 minutes or more at a time and that require moderate to vigorous levels of exertion."8 (Dr. Anyan is Professor of Pediatrics and Chief of the Division of Adolescent Medicine at Yale University School of Medicine.)
References
1. Kuczmarski RJ, et al. Increasing prevalence of overweight among US adults. The National Health and Nutrition Examination Surveys, 1969-1991. JAMA 1994;272:205-211.
2. Rosner B, et al. Percentiles for body mass index in U.S. children 5 to 17 years of age. J Pediatr 1998;132:211-222.
3. Cooper DM. Evidence for and mechanisms of exercise modulation of growth. Med Sci Sports Exerc 1994;26:733-740.
4. Rössner S. Childhood obesity and adulthood consequences. Acta Paediatr 1998;87:1-5.
5. Young BM. Television advertising and children. Oxford: Oxford University Press, 1990.
6. Strasburger VC. Children, adolescents and television. Pediatr 1992;13:144-151.
7. Andersen RE, et al. Relationship of physical activity and television watching with body weight and level of fatness among children. JAMA 1998;279:938-942.
8. Sallis JF, Patrick K. Physical activity guidelines for adolescents. Pediatr Exercise Sci 1994;6:302-314.
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