The purpose of this pilot study was to determine the prevalence of diabetes, pre-diabetes, and diabetes risk factors in eighth-grade students who were predominantly minority, to explore the role of race and ethnicity, and to evaluate the feasibility of collecting physical and laboratory data in the school setting.
This study showed that half of eighth-grade students and their families were willing to participate in a school-based health screening to determine risk factors for diabetes. The students who chose to participate in this study were representative of their schools' general populations with regard to race/ethnicity, sex breakdown, and percent with BMI ≥85th percentile. A small percentage (13%) of participants reported having a first-degree relative with diabetes. With the rise of diabetes in adults of Hispanic, African-American, and Native-American descent approaching 10% (14
), it had been anticipated that more students would have had a family history of diabetes.
Of the students who participated, 49% had a BMI ≥85th percentile for sex and age, 19.8% were at risk for overweight (BMI ≥85th and <95th percentile), and 29.2% were overweight (BMI ≥95th percentile). The 85th percentile, which is approximately equivalent to a BMI of 25 kg/m2
in adults, has been reported as the level above which youth develop type 2 diabetes (3
). Our BMI data are similar to what has been recently reported by Elkins et al. (15
), who showed that in low-income inner-city public school students with a mean age of 16 years, 44.4% of boys and 50.4% of girls had a BMI ≥85th percentile. However, our data showed higher rates of elevated BMI than reported in NHANES 1999–2000 (1
). In NHANES, 34% of children 6–19 years of age had a BMI ≥85th percentile, 20% were at risk for overweight, and 14% were overweight, indicating the difference is accounted for almost exclusively by the percent of subjects in the highest overweight category. Racial/ethnic differences were greater for individuals with a BMI ≥95th percentile than ≥85th percentile. There was a nearly 2.5-fold greater percentage of Hispanics and 3.5-fold greater percentage of Native American students compared with Caucasians in the overweight category.
The mean fasting glucose (98.2 mg/dl) was higher than values previously reported in population-based and clinical studies (1
). Ford et al. (17
) reported that fasting glucose levels have decreased by 2.5 mg/dl over the last decade from NHANES III (1988–1994) to NHANES 2000 (1999–2000). They reported mean values in 13-year-old subjects of 91.9 mg/dl in 1994 and 85.3 mg/dl in 2000; the lower value reported in NHANES may reflect the smaller percent of overweight and ethnic minority youth in the NHANES cohort compared with ours. Our mean fasting glucose was higher than values found in recent clinical studies. These studies either included a large percentage of prepubertal subjects (18
), who are known to have lower fasting glucose values, or a higher percentage of not only young children but also Caucasians and African Americans (16
), groups that also have lower mean values. Our mean fasting glucose data are similar to those described by Goran and Gower (19
) in subjects across the weight spectrum. For their subjects in Tanner stages 3–4, like our students, mean fasting glucose was 95.6 mg/dl for Caucasians and 96.2 mg/dl for African Americans—an identical mean value to that found in our African-American subjects.
Using the new American Diabetes Association cutoff of 100 mg/dl, a surprisingly high percentage (40.5%) of youth in our study had IFG. Because there were a large number of students with fasting glucose values between 100 and 110 mg/dl, the percentage with IFG would have been much lower (6.2%) if we used the previous cutoff for fasting glucose of 110 mg/dl. Very few studies have described the percentage of adolescents with IFG using the 100-mg/dl cutoff. Using the NHANES 2000 data, Duncan et al. (20
) found that 7.6% of adolescents had fasting glucose values ≥100 mg/dl, although nearly double the percent of Hispanic youth (13.5%) met this cutoff. Dolan et al. (21
) reported on a cohort of 2,501 primarily African-American and non-Hispanic white students in grades 5–12. They found 175 (7%) had IFG on initial screening in the school setting. The lower percentage with IFG might be due to the difference in racial/ethnic distribution (low percentage of Hispanic and Native American, high percentage of African American and Caucasian) and to there being only 40 youth in puberty.
A number of factors could account for the high percentage of our students with glucose dysregulation. It is likely our percentage with IFG was high, as was the mean fasting glucose, because our sample included a high percentage of overweight youth. IFG increased across BMI percentile categories. Another contributing factor was the high percentage of Hispanics and Native Americans in our cohort (about three-quarters of the students); 8–12% more Hispanic and Native American students had IFG compared with African Americans and Caucasians. Finally, our subjects, particularly the boys, were midpubertal, a time of innate insulin resistance. It is also possible that stress may have influenced our results. The setting in which phlebotomy was performed—a noisy crowded gym or assembly hall with each subject in view of peers and study personnel and without their parents—may have caused stress. Stress activation of the hypothalamic-adrenal axis could elevate cortisol and other counterregulatory hormones and thereby increase glucose values. This stress response may have downregulated by the time of the second blood draw 2 h later because students had become familiar with the procedure and had been kept quiet. We believe we did all we could to mitigate students eating or drinking before the blood draw, falsely elevating the number of subjects with IFG. Students were given ample opportunity to admit they were not fasting, reschedule the blood tests, and still receive the full $50 incentive.
Very few of our subjects had 2-h post–glucose load values in the IGT range (≥140 mg/dl). The 2-h glucose increased with BMI percentile, but there was no association of this value with race/ethnicity. Our findings are in contrast to studies done in overweight youth in clinical settings, where as many as 25% of subjects have been found to have IGT (16
). Children who seek medical attention due to obesity represent a cohort with more significant disease and/or a positive family history, making it much more likely they will have glucose dysregulation and IGT. We found that very few children had undiagnosed diabetes (fasting glucose ≥126 mg/dl and 2-h value ≥200 mg/dl), similar to multiple studies in overweight youth (16
Many subjects had elevated fasting insulin levels (mean value 30 μ
U/ml), indicative of insulin resistance (13
). There was a twofold increase in mean fasting insulin levels when comparing those with a BMI <85th percentile (22.5 μ
U/ml) to those with a BMI ≥95th percentile (44.8 μ
U/ml). Similarly, the percent with fasting insulin values >30 μ
U/ml increased by nearly 4.5-fold across the three BMI categories. Hispanics and Native Americans had the highest mean fasting insulin levels and a 1.5- to 2-fold increase in the percent with values ≥30 μ
U/ml. Our mean fasting insulin values are similar to the levels reported by Weiss et al. (16
) in obese and severely obese subjects (31.3 and 38.6 μ
U/ml, respectively). The same doubling across BMI percentiles was seen for the 2-h insulin values in our study.
In conclusion, the purpose of this study was to determine if there was a high enough percentage of students with IGT or diabetes to power a trial targeting these outcomes. Whereas we found a very low prevalence of both IGT and diabetes, our subjects exhibited a high prevalence of risk factors for diabetes. These included IFG (fasting glucose ≥100 mg/dl), hyperinsulinemia indicative of insulin resistance (fasting insulin ≥30 μ
U/ml), and BMI associated with diabetes risk (BMI ≥85th percentile). IFG is an accepted indicator of risk for type 2 diabetes and confers high likelihood that normal insulin secretion is already impaired (24
). In addition to defective insulin secretion, insulin resistance is generally present if type 2 diabetes is to develop. A fasting insulin level ≥30 μ
U/ml is suggestive of insulin resistance and is a measure that can be performed in the field setting. Almost 15% of the students were found to have all three of these risk factors for diabetes. These data suggest that strategies should be developed to reduce the prevalence of risk factors for diabetes.