Phenomenon of 'Double Diabetes' Common Among Blacks

In a cross-sectional study of adults with type 1 diabetes living in the Bronx, New York, not only were African Americans more insulin resistant than whites or Hispanics, they were also much more likely to have complications related to diabetes.

The researchers used a validated measure, estimated glucose disposal rate (eGDR) — which is calculated from glycated hemoglobin (HbA_1c), waist circumference, and the presence or absence of hypertension — to estimate insulin resistance.

The study, by Eric J. Epstein, MD, from the Montefiore Medical Center in the Bronx, and colleagues, was published online April 17 in Diabetes Care.

"In an urban clinic population of patients with type 1 diabetes, blacks were significantly less insulin sensitive than whites or Hispanics, and lower eGDR was associated with diabetes complications," Dr. Epstein and colleagues write. "Further study is needed to determine whether using eGDR to target interventions can improve outcomes."

Risk for "Double Diabetes"

Dr. Epstein and colleagues explain that in populations with high rates of type 2 diabetes and obesity, individuals with type 1 diabetes may share genetic and environmental factors that lead to reduced insulin sensitivity — a phenomenon sometimes referred to as "'double diabetes," although they note that this clinical phenotype has not been studied rigorously.

In the Bronx, 31% of adults are obese and 12% have diagnosed type 2 diabetes — among the highest rates in the US. Of the residents, 54% are Hispanic and 36% are black — ethnic groups that are at high risk for type 2 diabetes.

The researchers hypothesized that features of type 2 diabetes, including low eGDR, would be prevalent in the population of patients with type 1 diabetes seen in their clinic and that measured eGDR would correlate with increased risk for diabetes complications.

Of the 207 participants with type 1 diabetes who were enrolled in the study, 34% were white, 32% were Hispanic, and 34% were black. The participants had a mean age of 45, and 42% were women.

Blacks had a significantly lower mean eGDR (5.66 mg/kg/min) than Hispanics (6.70 mg/kg/min) or whites (7.20 mg/kg/min).

Participants whose eGDR was in the lowest tertile (that is, they had the most insulin resistance) were more likely to be black than white or Hispanic. They were also more likely to have a family history of type 2 diabetes or obesity.

Low eGDR was also linked with an increased risk of having the vascular complications of diabetes that were studied: cardiovascular disease, diabetic retinopathy, albuminuria, or stage 3 or higher chronic kidney disease.

"It is not surprising that a significant percentage of our type 1 diabetes clinic cohort shows features of 'double diabetes'…that is, evidence of type 2 diabetes features, in the lowest eGDR tertile," the authors write.

"This study corroborates previous reports that a low eGDR is associated with macro- and microvascular complications in type 1 diabetes," they add, noting that more research is needed.

"Larger prospective cohort studies can further assess the utility of eGDR in risk stratification for diabetes complications and how eGDR compares with currently used measures such as HbA_1c," they conclude.

The authors have reported no relevant financial relationships.

Diabetes Care. Published online April 17. Abstract