Although the incidence of type 2 diabetes (T2D) among persons with prediabetes is well known (∼10%/y), the incidence of prediabetes among normoglycemic persons is unclear. Also, in the Diabetes Prevention Program, no racial/ethnic differences were seen in diabetes incidence, whereas marked racial/ethnic disparities are reported in the prevalence of T2D. We aimed to obtain estimates of incident prediabetes and determine whether racial disparities manifest during transition to prediabetes.

We enrolled 376 (217 black, 159 white) nondiabetic offspring of parents with T2D (mean age 44.2 y) and followed them up quarterly for 5.5 years. Assessments included anthropometry, body composition, oral glucose tolerance test, biochemistries, energy expenditure, insulin sensitivity, and insulin secretion. The primary outcome was progression to impaired fasting glucose and/or impaired glucose tolerance (or diabetes).

Of 343 participants with evaluable data, 101 subjects (49 white, 52 black) developed prediabetes, and 10 (4 white, 6 black) developed diabetes during a mean follow-up of 2.62 years. There was no significant racial difference in the cumulative incidence of prediabetes (32.7% white, 30% black) or combined prediabetes/diabetes (35% white, 30% black). Significant predictors of prediabetes included age, gender, trunk fat, 2-hour postload glucose (2hrPG), insulin sensitivity, and insulin secretion. In a Cox proportional-hazards model, with adjustment for age and sex, the 2hrPG and abdominal obesity were independent predictors of incident prediabetes/diabetes [relative hazards (95% confidence interval [CI]) for the 90th vs 10th percentile: trunk fat mass 2.90 (95% CI 1.74–4.82), P < .0001; 2hrPG 2.54 (95% CI 1.46–4.40), P = .0009]. Having the trunk fat mass and the 2hrPG at the 90th percentile conferred a 7-fold hazard of prediabetes compared with persons at the 10th percentile for both measures.

Black and white offspring of parents with type 2 diabetes develop prediabetes at a similar high rate of approximately 11% per year. Therefore, close surveillance, with prompt intervention to prevent dysglycemia, is warranted in persons with parental diabetes.