adolescent obesity is equated to the proportion of those who are in the upper end of the BMI distribution—specifically, at or above the age- and gender-specific 95th percentile of the Centers for Disease Control and Prevention’s (CDC’s) BMI charts for children and youth aged 2 through 19 years2 (Kuczmarski et al., 2000) (see Chapter 3 for a more extensive discussion about the use of terms for childhood overweight and childhood obesity).

If BMI is normally distributed and survey-specific percentile distributions are presented, then by definition, 5 percent of children in each survey will be above the 95th percentile BMI of the survey sample. Thus, reports based on the survey-specific BMI percentiles would always designate 5 percent of children as obese and would fail to detect any true increasing prevalence of obesity across surveys. The CDC therefore developed a revised growth reference in 2000 that established the age- and gender-specific 95th percentile of BMI. The growth reference data were based on BMI distributions from national surveys between 1963 and 1980 for children aged 6 to 19 years, and between 1971 and 1994 for children aged 2 through 5 years (Kuczmarski et al., 2002; Ogden et al., 2002b). There are no BMI-for-age references or accepted definitions for children younger than 2 years of age. However, the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) has defined the term overweight for children under 2 years who are at or above the 95th percentile of weight-for-length and uses this standard for determining WIC program eligibility (Ogden et al., 2002a).

Overall Burden

The term “epidemic” suggests a condition that is occurring more frequently and extensively among individuals in a community or population than is expected. This characterization clearly appears to apply to childhood obesity. In 2000, obesity was two to three times more common in children and youth than in a reference period in the early 1970s. The increase in obesity prevalence has been particularly striking since the late 1970s. The obesity epidemic affects both boys and girls and has occurred in all age, race, and ethnic groups throughout the United States (Ogden et al., 2002a).

The 1999-2000 NHANES found that approximately 10 percent of 2-to 5-year-old children were at or above the 95th percentile of BMI, repre-

2

The NHANES series use the term “overweight” rather than “obese” to describe all children who are at or above the age- and gender-specific 95th percentile of BMI. However, this report uses the term “obese” to refer to those children (see Chapter 3).



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