It is well accepted that overweight as a child is a risk factor for obesity in adulthood. Using data from the Fels Longitudinal Study, Guo et al. (76) correlated girls' percent ideal body weight aged 10-18 with their percent ideal weight at age 35; all coefficients exceeded 0.6. We know that obesity, impaired glucose tolerance and insulin resistance are important metabolic risk factors for Type 2 diabetes mellitus (77, 78), and they are also suspected to be important etiologic components of youth-onset disease.
Defining obesity in growing children and adolescents is more problematic than in adults, and various investigators have relied on skinfolds, body mass index (BMI; defined as weight/height2), ponderosity (weight/height3), and other methods (79). Irrespective of which of these measures is used, most secular analyses indicate that adiposity has increased among US youth since 1960. Comparing data from four US national surveys collected between 1963 and 1980, Gortmaker et al. (80) reported that the prevalence of obesity increased by 54% among children aged 6-11, and 39% in adolescents aged 12-17. These investigators defined obesity as triceps skinfold thickness >85th percentile of the 1963-65 National Health Examination Survey 2 (NHES-2) distribution. Among young African Americans (ages 6-11) the prevalence of obesity doubled from 8.8% in 1963-65 to 16.8% in 1976-80, while among black adolescents the corresponding rates were 10.2% and 18.7%. By 1976-80, fully 25.1% of black females and 12.7% of black males aged 12-17 were obese. However, using BMI in a similar analysis of four national datasets (two of which were the same as Gortma-ker's), Harlan et al. (81) found no significant increases in obesity among whites or blacks 12-17 years old. A more recent comparison of the second and third National Health and Nutrition Examination Surveys [NHANES-II (1976-80) and NHANES-III (1988-91)] showed that the prevalence of overweight, defined as BMI >85th percen-tile from NHES, increased from 15% to 21%
among youth aged 12-19 years (82). Cross-sectional anthropometric surveys of Mexican American children were conducted in Brownsville, Texas in 1972 and again in 1983 (83). Mean BMI and triceps skinfold increased significantly over the 11-year interval except among boys >15 years old. In preparation for an intervention study in 4th grade Mexican American children in Texas, baseline data were collected in 1997-98 on 173 subjects: 21% of boys and 18% of girls were overweight, defined as age- and sex-specific BMI >85th percentile of the 2nd National Health Examination Survey (84). Of these children 60% reported a first-or second-degree relative with diabetes.
Other investigators in the US report similar high levels of overweight along with physical inactivity in children and adolescents in various geographic locations. A survey of 522 schoolgirls aged 10-18 in 1991 recorded overweight (>85th percentile in NHANES-1) in 22% of non-Hispanic white, 37.6% of non-Hispanic black, and 26.7% of Hispanic girls in Lynn, Massachusetts (85). More than 75% of these girls reported watching television >2 hours per day, and only 13% participated in strenuous physical activity >3 times per week. In preparation for an intervention trial among 4th graders in Baltimore, survey data were collected in 1995 from 785 students from primarily African American, low-income schools. They reported, on average, watching >4 hours of television per day (86).
A US national survey of adolescents conducted in 1996 demonstrated large ethnic differences in reported inactivity, but less of a disparity in moderate-vigorous physical activity (87). Average television/video use was 20.4 hours/week for non-Hispanic blacks and 13.1 for non-Hispanic whites. Non-Hispanic black and Asian girls had the lowest levels of physical activity. The increasing prevalence of obesity and physical inactivity among children provides a disconcerting glimpse of future generations, as recent longitudinal studies of the rate of fat accretion in children have revealed that a major determinant is parental fatness (88).
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