Changes in the prognosis of Japanese patients who developed type 1 diabetes before the age of 30 years.

Aims: We investigated changes in vital prognosis according to the year at diagnosis of type 1 diabetes mellitus (T1DM) in a hospital-based survey.

Methods: Of 1054 Japanese subjects diagnosed as T1DM between 1952 and 1999 before the age of 30 and consulted the diabetes center between 1962 and 1999, the survival status up to 2010 or 20 years of follow-up was investigated. Subjects were divided by the year at diagnosis of T1DM: before 1979 (Group A: n = 359), 1980 to 1989 (Group B: n = 400), and 1990 to 1999 (Group C: n = 295). The mortality (/100,000 person years) and standardized mortality ratio (SMR) were calculated, and the effect of year at diagnosis of T1DM was explored by the Cox proportional hazard model.

Results: The survival status was confirmed in 90.0%. The mortality rate (95%CI) and age and sex adjusted SMR (95%CI) were 457 (288-627) and 3.0 (1.9-4.2) in Group A, 265 (143-387) and 2.2 (1.2-3.2) in Group B, and 144 (29-259) and 1.6 (0.3-2.9) in Group C, respectively. The cumulative survival rate was significantly different according to the year at diagnosis of T1DM (p = 0.0239). Cox's proportional hazard model revealed that Groups B and C had significantly lower risks of death than Group A after adjustment for gender and age at diagnosis of T1DM (HR 0.48 [95%CI 0.26-0.87] for Group B and HR 0.25 [95%CI 0.09-0.60] for Group C).

Conclusion: This study indicated that vital prognosis is improving according to the year at diagnosis of T1DM and suggested the need of a nationwide survey.