obesity rates level off (Narayan et al., 2003). Nearly all children with type 2 diabetes are obese, and a disproportionate number are Native American, African American, Hispanic, or Asian/Pacific Islander (Fagot-Campagna et al., 2000; Goran et al., 2003; Davis et al., 2004).
Several risk factors—including increased body fat (especially abdominal fat), insulin resistance, ethnicity, and the onset of puberty—have been identified as contributors to the development of type 2 diabetes, and they appear to have an additive influence (Goran et al., 2003). Accurate estimates of the prevalence of diabetes in U.S. children are difficult to determine. It has been estimated that the prevalence of diabetes is 0.41 percent in U.S. youth aged 12-19 years (approximately 100,000 U.S. adolescents) and the prevalence of impaired fasting glucose is 1.76 percent (approximately 500,000 U.S. adolescents) (Fagot-Campagna et al., 2001). Better estimates for children are not possible because the prevalence of type 2 diabetes in this population is still relatively low. NHANES is the only current national data collection effort that could potentially make such an estimate. However, the sample sizes from NHANES are not large enough to make a stable point estimate of the prevalence.
The childhood obesity epidemic may result in increased risk of type 2 diabetes. One study found that for each adolescent diagnosed with type 2 diabetes, there are 5 others with impaired fasting glucose, an indicator of insulin resistance below the diagnostic threshold for type 2 diabetes (Fagot-Campagna et al., 2001). Furthermore, the degree of insulin resistance in children increases with the severity of body fatness, as it does in adults (ADA, 2000). Thus, the combination of more obese children and the increased severity of obesity suggests that larger numbers of children will reach the diagnostic threshold for type 2 diabetes. Finally, it is estimated that approximately three-fourths of obese adolescents will be overweight as young adults (Guo et al., 2002) and will likely face the persistent risk of developing type 2 diabetes.
The increased prevalence of obesity among adults of all ages also has been associated with a similar increase in the prevalence of diabetes (Mokdad et al., 2001). In fact, the increase in diabetes prevalence has been greatest in young adults aged 30 to 39 years, with prevalence almost doubling between 1990 and 2001 (Mokdad et al., 2000, 2003). Moreover, the development of all of the major complications of diabetes, including retinopathy, nephropathy, and neuropathy, are related to duration of disease. Those who develop diabetes earlier in life generally will develop costly complications earlier with the potential for premature mortality. For example, among 79 individuals in a Canadian referral clinic who were diagnosed with type 2 diabetes before the age of 17 and who were followed up from ages 18 to 33 years, two had died suddenly while on dialysis and three more were currently receiving dialysis (Dean and Flett, 2002).