Our data demonstrate that African American adolescents and young adults with type 2 diabetes have increased arterial stiffness compared to Caucasians after controlling for age, sex, BMI and BP. Our race specific regression models suggest this process is mediated by age, obesity and blood pressure. However, compared to Caucasians blood pressure appears to have less of an effect on arterial stiffness in African Americans while the effects of obesity appear equal between the two groups. In addition, we found an independent effect of HDL-cholesterol and duration of diabetes on arterial stiffness in Caucasians which was not observed in African Americans. Thus, our data demonstrate arterial stiffness in adolescents with type 2 diabetes is mediated by different cardiovascular risk factors. Moreover, these data suggest while weight reduction and blood pressure management may improve arterial stiffness in both ethnic groups, improvement in lipid profile and diabetes prevention may only reduce arterial stiffness in Caucasians.
Cross sectional studies in pediatrics have reported racial differences in arterial stiffness but these studies have not been conducted in adolescents with type 2 diabetes. Thurston et al demonstrated significantly increased pulse wave velocity in overweight (average body mass index 24.4 ± 0.4kg/m2) African Americans adolescents without diabetes compared to their age and body mass index matched Caucasian counterparts [13
]. In a study of normal weight youth, Collins et al described increased brachial pulse wave velocity in African Americans compared to Caucasians, p<0.05 [14
]. Hlaing et al conducted the only longitudinal study in children and found that African-Americans demonstrated increased arterial stiffness at age 7 compared to Caucasians, but these differences in arterial stiffness did not persist after age 12 [15
]. However, their findings were observed in a younger population without diabetes. Our study is the first to examine racial differences in arterial stiffness in adolescents with type 2 diabetes. We demonstrate early in the course of type 2 diabetes (average duration of 3.6 ± 2.7 years) African American adolescents with type 2 diabetes have increased arterial stiffness compared to their age-matched Caucasian counterparts.
In adults, many theories have been proposed as to why African Americans demonstrate higher rates of morbidity and mortality from type 2 diabetes. This process is thought to be mediated by a higher prevalence of cardiovascular risk factors including hypertension, obesity and insulin resistance [16
]. The Insulin Resistance Atherosclerosis Study (IRIS), a large observational cohort study in adults, suggested this process may not only be mediated by higher blood pressure but also higher hemoglobin A1c levels [17
]. Additional information from the Atherosclerosis Risk in Community (ARIC) study has suggested increased arterial stiffness in African Americans is likely due to independent contributions of hypertension, the presence of diabetes and socioeconomic status [18
]. To date, potential mediators which may contribute to differences in arterial stiffness among African American and Caucasians in adolescents with type 2 diabetes have not been studied.
In contrast to adult studies, we demonstrate that the increased arterial stiffness observed in African Americans is not explained by differences in traditional risk factors alone, as the degree of BMI, lipid and blood pressure elevation observed among the African American and Caucasian adolescents and young adults in our study was not different. Our regression models suggest increased arterial stiffness in African Americans is partially mediated by age, blood pressure and obesity but compared to Caucasians the contribution from obesity is similar and that from blood pressure appears less. Additionally diabetes risk factors and lipids to do not appear to contribute to increased stiffness in African Americans. These findings suggest other mechanisms are likely involved.
Other investigators have suggested arterial stiffening may be mediated by increased insulin resistance or central adiposity [19
]. Additionally, hypoadiponectinemia may contribute to arterial stiffness by reducing endothelial activation [21
]. Finally, adult studies have suggested increased endothelin-1 levels, a potent vasoconstrictor released from the endothelium which impairs blood flow in large arteries may be higher in African Americans compared to Caucasians [22
]. In this study, these parameters were not measured. Thus, further investigation is needed to examine the role of potential mediators which may explain increased arterial stiffness in type 2 diabetes.
This study is limited in our cross-sectional design as it can not identify causality and it provides only a single measurement in time. In addition, we were unable to assess other “non-traditional risk factors” which may contribute to increased vascular stiffness in both race groups such as increased small LDL particles, increased lipoprotein (a), increased serum homocysteine levels and as mentioned, endothelin-1 levels. Also, socioeconomic variables were not considered in the current analysis.
Despite these limitations, this is the first study to provide evidence that racial discrepancies in vascular stiffness exist in adolescents and young adults with type 2 diabetes while identifying cardiovascular risk factors which contribute to arterial stiffness by race group. Beginning in the fourth decade African American adults are known to have higher rates of diabetes and cardiovascular complications including myocardial infarction [3
] and stroke [2
]. Our findings suggest given the increased prevalence of type 2 diabetes in the adolescent population, these complications may be seen earlier. Thus aggressive approaches to prevent the development of type 2 diabetes should be taken in the pediatric population.