All-Cause Mortality in the Canterbury (New Zealand) Insulin-Treated Diabetic Registry Population

Abstract

OBJECTIVE— To establish all-cause death rates and life expectancies of and risk factors for mortality in insulin-treated diabetic individuals living in Canterbury, New Zealand. RESEARCH DESIGN AND METHODS— Insulin-treated diabetic subjects(n = 1,008) on the Canterbury Diabetes Registry were tracked over 9 years, and their vital status was determined. Death rates were standardized using direct and indirect methods. Cox proportional hazard regression was used to model the effects of demographic and clinical covariates on survival time. RESULTS— At study entry, age ranged from 2.9 to 92.7 years,with mean 48.7 ± 20.4 years; age at diagnosis was 0.2-88.9 years, mean 34.5 ± 20.0 years; and duration of diabetes was 0.1-58.5 years, mean 14.0 ± 10.6 years. There were 303 deaths in 7,372 person-years of follow-up with a standardized mortality ratio (SMR) of 2.6 (95% CI 2.4-3.0). Relative mortality was greatest for those aged 30-39 years (SMR 9.2[4.8-16.2]). The death rate for the diabetic cohort standardized against the Segi world standard population was 16.2 per 1,000. Attained age, sex, and clinical subtype were significant predictors of mortality. The SMR for subjects with type 1 diabetes and age at onset <30 years was 3.7 (CI 2.7-5.0), 2.2 (1.8-2.6) for those with onset ≥30 years, and 3.1 (2.5-3.7)for subjects suspected of having latent autoimmune diabetes in adulthood or insulin-treated type 2 diabetes. Life expectancy was reduced for both sexes at all ages. CONCLUSIONS— Mortality rates for insulin-treated diabetic individuals remain high, resulting in shortened life spans relative to the general population. Marked differences in mortality exist between clinical groups of subjects. Further research is needed to improve diabetes classification and to clarify differences in health outcomes.