Using the most recent NHANES data, we estimated that the national population-based prevalence rates of IFG, IGT, and pre-diabetes among U.S. adolescents aged 12–19 years were 13.1, 3.4, and 16.1%, respectively. IFG accounted for nearly 80% of adolescents with pre-diabetes. Pre-diabetes risk was positively associated with being male and having hyperinsulinemia and negatively associated with being a non-Hispanic black. Moreover, hyperinsulinemia appeared to account for the association of weight status and clustering of cardiovascular risk factors with pre-diabetes.
The prevalence of IGT has been found to be high among adolescents with obesity (21%) (5
) or those with a positive family history of type 2 diabetes (25%) (6
) and in particular among those with both obesity and a positive family history of type 2 diabetes (35%) (7
). In contrast, several school-based studies have reported a relatively low prevalence of IGT. In Poland, the prevalence of IGT was found to be 0.3% among all children and adolescents aged 8–19 years but 7.1% among those who were obese (8
). The results of the Studies to Treat or Prevent Pediatric Type 2 Diabetes (STOPP-T2D) indicated that the prevalence of IGT was 2.3% among all eighth graders in four middle schools of Southern California, Texas, and North Carolina but 4.1% among those who were overweight (9
). In the Princeton School District of Cincinnati (10
), IGT was detected among only 0.5% of 5th to 12th graders. It is possible that sampling and geographic variations may account for these low prevalences. To the best of our knowledge, our study is the first report on the prevalence estimate of IGT using a nationally representative sample of U.S. adolescents. Our IGT prevalence estimates among all adolescents (3.4%) and among overweight adolescents (9.5%) were lower than the rates reported in clinic-based studies but higher than the rates reported in school-based studies.
Our estimated IFG prevalence of 13.1% among U.S. adolescents in 2005–2006 was 87.1% higher than the 7% estimated from NHANES data in 1999–2000 (11
). Rapid increases in the prevalence of central obesity (19
) among adolescents may be a factor in the increased prevalence of IFG. Our results indicated that overweight adolescents had a nearly twofold higher prevalence of IFG than did those with normal weight.
It is noteworthy that adolescents with two or more of the four cardiometabolic risk factors (i.e., central obesity, high triglyceride, low HDL cholesterol, and elevated blood pressure) had a significantly higher prevalence of pre-diabetes than those with zero or one risk factor. These findings, which were in agreement with those from previous studies (6
), have several clinical implications. The presence of two or more cardiometabolic risk factors among adolescents may be an indication that their pre-diabetes status should be assessed. Because pre-diabetes is an intermediate stage in the development of type 2 diabetes and has been shown to be reversible through pharmacological and lifestyle interventions (20
), early detection and appropriate management of pre-diabetes among adolescents could effectively prevent or delay their development of type 2 diabetes in later life.
As previous studies have shown (5
), we found that adolescents with pre-diabetes had significantly higher fasting insulin levels than those without pre-diabetes. In one previous study, insulin resistance was found to be the best predictor of 2-h plasma glucose in an OGTT among obese adolescents (5
). It has been proposed that insulin resistance is a major underlying cause of type 2 diabetes (21
), and intramyocellular and intra-abdominal lipid accumulation is highly associated with the development of insulin resistance (22
). Our results indicated that hyperinsulinemia or insulin resistance may play an important role in the association of obesity and clustering of cardiometabolic risk factors with pre-diabetes. The prevalence of hyperinsulinemia has increased by ~35% in the past decade among U.S. adults (23
). Therefore, early identification and effective treatment of insulin resistance could prevent or delay the occurrence of pre-diabetes and diabetes among both adolescents and adults (24
Similar to the finding of a previous study (10
), our results demonstrated that only 2.9% of adolescents with glucose intolerance had both IFG and IGT. IFG and IGT may identify different populations at risk of developing diabetes. It has been proposed that IFG and IGT represent distinct metabolic abnormalities with different etiological mechanisms, with IFG being caused by impaired basal insulin secretion and IGT being caused primarily by peripheral insulin resistance (25
). Despite these etiological differences, however, IFG and IGT have both been associated with an increased risk of developing diabetes and subsequent cardiovascular disease (1
), and, as we showed, both are strongly associated with obesity and clustering of cardiometabolic risk factors before adjustment for hyperinsulinemia. Therefore, from a public health point of view, it seems tenable to use the term “pre-diabetes” to describe the condition of IFG and/or IGT and to identify adolescents at increased risk for diabetes in later life.
Our results are subject to two limitations. First, the cross-sectional design of the NHANES study precluded a causal inference among obesity, clustering of cardiometabolic risk factors, insulin resistance, and pre-diabetes. Future studies with a longitudinal design are warranted to identify the temporal sequence among these variables. Second, because of the low prevalence of IGT, we were unable to conduct separate analyses of factors associated with IGT. Therefore, our results for pre-diabetes may be influenced mainly by IFG. However, because our study was focused on pre-diabetes prevalence estimates rather than its predictors, interpretation of our results may not be affected.
In summary, the high prevalence of pre-diabetes among adolescents has raised public health concerns. Because adolescents with pre-diabetes usually have no apparent clinical symptoms, great efforts may be needed to identify them early and to intervene against the root causes of insulin resistance such as overweight, physical inactivity, and unhealthy diet in pediatric primary care and through public health services.