Racial and Ethnic Differences in an Estimated Measure of Insulin Resistance Among Individuals With Type 1 Diabetes

OBJECTIVE

Insulin resistance is greater in racial/ethnic minorities than in non-Hispanic whites (NHWs) for those with and without type 2 diabetes. Because previous research on insulin resistance in type 1 diabetes was limited to NHWs, racial/ethnic variation in an estimated measure of insulin resistance in type 1 diabetes was determined.

RESEARCH DESIGN AND METHODS

The sample included 79 individuals with type 1 diabetes diagnosed at age <18 years (32.9% NHWs, 46.8% non-Hispanic black [NHB], 7.6% other/mixed, and 12.7% Hispanic) and their families. Estimated glucose disposal rate (eGDR) (milligrams per kilogram per minute; a lower eGDR indicates greater insulin resistance) was calculated using A1C, waist circumference, and hypertension status.

RESULTS

Mean current age was 13.5 years (range 3.2–32.5) and diabetes duration was 5.7 years (0.1–19.9). eGDR was inversely associated with age. Compared with that in NHWs, age-adjusted eGDR was significantly lower among nonwhites (NHB, other/mixed, and Hispanic: Δ = −1.83, P = 0.0006). Age-adjusted eGDR was negatively associated with body fat, triglycerides, urinary albumin/creatinine, acanthosis nigricans, parental obesity, and parental insulin resistance and positively related to HDL and sex hormone–binding globulin. In multivariable analysis, lower eGDR was significantly associated with older age, nonwhite race/ethnicity, acanthosis, and lower HDL.

CONCLUSIONS

Minorities with type 1 diabetes are significantly more insulin resistant, as measured by eGDR, than NHWs. Exploring potential mechanisms, including disparities in care and/or physiological variation, may contribute to preventing racial/ethnic differences in insulin resistance–associated outcomes.Insulin resistance is common in type 2 diabetes (1) and seems to play a role in the natural history (2) and risk of complications (3) in type 1 diabetes as well. Measurement of insulin resistance in type 1 diabetes is difficult because methods used in nondiabetic and type 2 individuals, e.g., insulin or homeostasis model assessment (4), cannot be used in hypoinsulinemia. The euglycemic-hyperinsulinemic clamp has been used; however, it is labor-intensive and invasive and therefore is not suitable for population-based studies. In response, a derived measure of insulin resistance, the estimated glucose disposal rate (eGDR), has been developed using clinical measures and is strongly correlated with clamp-measured insulin resistance (5).Consistent with clamp studies in type 1 diabetes (2), lower eGDR is associated with older age (6), longer duration of diabetes (6), greater adiposity (6), family history of type 2 diabetes (5), poor glycemic control (5), and elevated lipids (6). Low eGDR predicts incident retinopathy (3), nephropathy (3,6), neuropathy (7), and cardiovascular disease in type 1 diabetes (3,6). These findings are primarily based on non-Hispanic white (NHW) adults.Previous research shows racial/ethnic differences in insulin resistance for healthy individuals and those with type 2 diabetes. For example, minority adults with and without type 2 diabetes were more insulin resistant than their NHW counterparts (1,8). Similarly, in nondiabetic youth, minorities were more insulin resistant than NHWs (9,10). Despite these findings, to our knowledge, there are no data on insulin resistance in minorities with type 1 diabetes.Therefore, we sought to determine 1) whether racial/ethnic differences in insulin resistance, as measured by eGDR, exist in type 1 diabetes and 2) whether the association of eGDR with factors traditionally related to insulin resistance differed by race/ethnicity. It was hypothesized that insulin resistance is greater in minorities than in whites and that associations with insulin resistance are consistent across race/ethnicity.