The SEARCH-Navajo study is the first population-based study to provide estimates of diabetes prevalence and incidence among Navajo youth. We found that diabetes was infrequent in youth aged <10 years; however, both prevalence and incidence of diabetes were high in older youth, especially adolescents aged 15–19 years. In this age-group, 1 in 359 Navajo youth had diabetes in 2001 and 1 in 2,542 developed diabetes annually. The majority of diabetes among Navajo youth was type 2 diabetes, although type 1 (autoimmune) diabetes was present, especially among younger children. Of all racial/ethnic groups in the SEARCH study, Navajo youth aged 15–19 years had the greatest risk of type 2 diabetes (14
). In contrast, the rates of type 1 diabetes in Navajo youth were the lowest of all SEARCH study racial/ethnic groups (14
Data on prevalence of diabetes in Navajo youth are minimal. There are virtually no data on diabetes incidence, and no differentiation according to diabetes type was published. An earlier study (7
) of 160 Navajo youth aged 12–19 years found that the prevalence of impaired glucose tolerance or undiagnosed diabetes was 8%. In 1999, Kim et al. (6
) screened 234 high school student volunteers with oral glucose tolerance tests. One student was found to have diabetes (0.4%) and 3% had impaired glucose tolerance or impaired fasting glucose. Recent efforts by Navajo area IHS investigators are focused on a more comprehensive assessment of the current burden of diabetes in Navajo youth (C.A., personal communication). The majority of data on diabetes among American Indian youth come from population-screening studies, such as the Pima Indian study (1
). The prevalence of type 2 diabetes among Pima Indians of Arizona is much higher than reported here for Navajo youth (37.8 and 53.1 per 1,000 among Pima male and female subjects aged 15–19 years, respectively, vs. 2.07 and 2.63 per 1,000 in Navajo male and female subjects aged 15–19 years, respectively). Similarly, the incidence rates of type 2 diabetes are >10-fold higher among Pima youth aged 5–14 years (331.9 per 100,000 per year) than among Navajo youth (19
). These data may reflect population differences in risk for type 2 diabetes but are also partly due to systematic screening for case ascertainment among the Pima Indians.
Using the IHS database, Acton et al. (20
) recently found that the prevalence of all diabetes among American Indian/Alaska Native youth aged 15–19 years was 5.4 per 1,000, a figure much closer to that reported here (2.78 per 1,000), although this study did not conduct case validation through medical record abstraction. Our experience is that ~50% of cases identified through the Navajo IHS database in youth aged <20 years were not valid diagnoses of diabetes, due largely to miscoding. Another recent study (21
) conducted between 1999 and 2001 among American Indian youth aged <20 years in Montana and Wyoming used methods similar to the SEARCH study (case identification through the IHS database followed by medical record validation). In these populations, the prevalence and incidence of diabetes were similar to those reported for Navajo Indians (prevalence estimates were 0.7 and 1.3 per 1,000 and incidence rates were 5.8 and 23.3 per 100,000 per year for type 1 and type 2 diabetes, respectively).
Our study also provides important descriptive information on characteristics of diabetes type, as well as risk factors for chronic complications. Disturbingly, 40–50% of youth with diabetes had poor glycemic control. In addition, there was a high prevalence of obesity and related cardiometabolic disturbances (central fat deposition, dyslipidemia, and hypertension), especially among type 2 diabetic youth (). No such information was previously available in youth with diabetes, although one of the earliest studies (6
) of nondiabetic Navajo youth found them to have higher BMI levels, with higher triglyceride and lower HDL cholesterol levels than NHW youth. Coupled with high prevalence of unhealthy behaviors (smoking, high-fat diets, and sedentary lifestyles) and lower socioeconomic status (), these findings may translate to an increased prevalence of cardiovascular disease in the future as these youth mature.
There are a several potential limitations to this study. We did not include Navajo Indians who received services from non-IHS providers. Because the IHS facilities provide universal health care coverage to all American Indian/Alaskan Native people, we do not believe that our ascertainment approach excluded an important number of youth with diabetes. We did not attempt to assess how much undiagnosed diabetes existed through screening. We may, therefore, have underestimated the true risk of type 2 diabetes in Navajo youth. Similar to other population-based studies (1
), our analyses utilized diabetes type assignments made by health care providers. Diabetes type was further characterized in a subset of Navajo youth participating in the research visit. With a clinical diagnosis of type 1 diabetes, GAD65 antibody positivity was present in almost 50% of individuals (), similar to other racial/ethnic groups participating in the SEARCH study (14
). The GAD65-negative participants with type 1 diabetes may have lost GAD positivity, may be positive for other autoantibodies, or may have other causes of insulin deficiency. With a clinical diagnosis of type 2 diabetes, 20.3% of Navajo participants had positive GAD65 antibodies, which is similar to other racial/ethnic groups participating in the SEARCH study (14
), as well as other smaller U.S. studies (23
). The role of autoantibody positivity in the etiology and natural evolution of diabetes among youth with a clinical phenotype of type 2 diabetes requires further exploration.
Our data provide strong evidence that diabetes is an important health problem for Navajo youth. Because young people with diabetes will have more years of disease burden and an increased risk of developing diabetes-related complications early in life, targeted efforts aimed at primary prevention of diabetes in Navajo youth and efforts to prevent or delay the development of chronic complications among those who already developed diabetes are warranted.