This analysis found that among the almost 4% (2.7 million) of U.S. children who have a BMI ≥99th percentile for age/gender (1999–2004), there were significant differences by race, gender and poverty. The higher prevalence among Black and Mexican-American youth and among youth of lower income reflects the associations between these groups and the larger group of children with BMI ≥95th
percentile. Overall, prevalence of BMI ≥99th percentile has increased by over 300% since 1976, and by over 70% since 1994. This analysis also demonstrated a high prevalence of teens with BMI ≥40 kg/m2
(>400,000). This level of severe adiposity is part of the initial criteria for considering bariatric surgery in adolescents. (12
) Given the immediate and future health risk and costs associated with this growing prevalence, these groups need more careful attention.
Higher socio-economic positions seem to protect against morbid and severe obesity. Explanations for this association may include the easy availability and low cost of energy-dense snacks in poor, inner-city neighborhoods. (30
) In contrast, fresh fruits and vegetables are often not available, and adequate amounts are expensive. (31
) Recent reports confirm the seemingly paradoxical connection of poverty, food insecurity, and obesity. (21
) Even more surprising is that the risk may carry through to the morbidly and severely obese. The effect of poverty on levels of physical activity is unknown. One report showed an increased risk of obesity in 7 year olds when they perceived their neighborhood as unsafe (32
), whereas others have shown an inverse effect of income on sedentary activity. (33
) All of these findings implicate the environment as an important factor, but one over which the child has little control. Most worrisome is that vulnerable populations are experiencing the worst increase in severe obesity, as rates in Whites and the affluent have plateaued.
Many cardiovascular risk factors, such as higher waist circumference, insulin resistance (evidenced by elevated fasting insulin), blood pressure, and lower HDL cholesterol, were associated with BMI ≥99th percentile in this study. The application of adult criteria of the metabolic syndrome to this population showed upwards of a third met the criteria. The higher rates of elevated ALT among severely obese youth supports the recent Expert Committee Recommendations for pediatric primary care providers to routinely assess liver transaminases as a screen for non-alcoholic fatty liver disease. These findings demonstrate the significant health risks facing this morbidly obese group.
Anthropometric cutpoints for severe obesity in youth are sought in order to guide use of aggressive interventions, like bariatric surgery, that may be more effective but have higher risk and costs than behavior-based treatment. (34
) Recent criteria for identification of adolescents for bariatric surgery propose absolute BMI ≥40 with a co-morbidity (12
) but this cutpoint may not capture those younger adolescents who have dangerous levels of obesity despite having a BMI < 40 kg/m2. BMI ≥99th
percentile is a cutpoint that identifies greater risk of later obesity and cardiovascular complications compared with obese children with lower BMI percentile. (9
) In addition, this cutpoint identifies the same deviation from median BMI across ages and genders. In contrast, BMI of 40 kg/m2
defines a higher deviation from median BMI in younger adolescents compared with older adolescents and in boys compared with girls. Greater than 99th
percentile, because it accounts for age and gender, can be applied to pre-adolescents and even preschool children. Although surgery and medication are not appropriate for these younger children, increased resources to support intensive behavior-based programs may lead to an effect that justifies greater cost. Classification of severe obesity allows assessment of the health burden and the healthcare system needs of these children. Treatment of hypercholesterolemia and diabetes is reimbursable by insurers, yet these diseases are quite rare across pediatric populations (0.8% of US teens have hypercholesterolemia requiring pharmacotherapy (35
), and only 0.18% have diabetes (36
)). The higher prevalence of severe childhood obesity among generally disadvantaged sectors of society heightens the need for greater research, prevention, and treatment efforts, as well as a coordinated approach to public health efforts.
Limitations to our analysis include small sample sizes among some minority groups with a BMI ≥40 kg/m2
. As with other analyses using NHANES, results with small sample sizes may have relative large standard errors (> 30%) and could therefore be statistically unstable and should be interpreted with caution. The tables identify these comparisons, most common in the NHANES II cohort. The data are cross-sectional, and causality cannot be inferred from any of the associations found. Poverty income ratio is an imperfect marker of SES, with other factors such as parent education levels, being superior measures of socio-economic position. (37