Changes in Mortality in People With IGT Before and After the Onset of Diabetes During the 23-Year Follow-up of the Da Qing Diabetes Prevention Study

OBJECTIVE: People with impaired glucose tolerance (IGT) have increased risk of mortality and a high risk of progression to diabetes, but the extent that the excess mortality is associated with IGT per se or is the result of subsequent diabetes is unclear. RESEARCH DESIGN AND METHODS: We compared mortality before and after the development of diabetes among 542 persons with IGT initially who participated in a 6-year lifestyle diabetes prevention trial and were followed-up from 1986 to 2009. RESULTS: During the 23-year follow-up, 174 (32.1%) died, with an overall death rate of 15.9/1,000 person-years. The majority of deaths (74.7%; 130 of 174) occurred after progression to type 2 diabetes, with age-adjusted death rates of 11.1/1,000 person-years (95% CI 8.2–12.0) before and 19.4/1,000 person-years (95% CI 11.9–23.3) after the development of type 2 diabetes. The cumulative mortality was 37.8% (95% CI 33.1–42.2%) in participants who developed type 2 diabetes during first 10 years of follow-up, 28.6% (95% CI 21.6–35.0%) in those who progressed to type 2 diabetes in 10–20 years, and 13.9% (95% CI 7.0–20.3%) in those who did not develop to type 2 diabetes within 20 years. Time-dependent multivariate Cox proportional hazards analyses, with adjustment for baseline age, sex, intervention, and other potential confounding risk factors, showed that the development of type 2 diabetes was associated with a 73% higher risk of death (hazard ratio 1.73 [95% CI 1.18–2.52]). CONCLUSIONS: As elsewhere, IGT is associated with increased risk of mortality in China, but much of this excess risk is attributable to the development of type 2 diabetes.