Temporal Trends in Mortality Associated with Comorbid Type 2 Diabetes and Schizophrenia: The Fremantle Diabetes Study

In Phase I of the community-based Fremantle Diabetes Study (FDS1), there was evidence of a deleterious interactive effect of schizophrenia and type 2 diabetes on mortality. Our aim was to investigate whether the mortality gap had improved in FDS Phase II (FDS2) conducted 15 years later.

Participants with type 2 diabetes from FDS1 (n = 1291 recruited 1993-1996) and FDS2 (n = 1509 recruited 2008-2011) were age-, sex- and postcode-matched 1:4 to people without diabetes. Schizophrenia at entry and incident deaths were ascertained from validated administrative data.

Schizophrenia affected 50/11,195 (0.45%) of participants without diabetes and 17/2800 (0.61%) of those with type 2 diabetes (p = 0.284). During 142,304 person-years of follow-up, the mortality rate (95% CI) was lowest for the FDS2 subgroup without diabetes/schizophrenia (18.2 (16.9, 19.6)/1000 person-years) and highest in FDS2 and FDS1 subgroups with type 2 diabetes/schizophrenia (53.3 (14.5, 136.6) and 98.0 (31.8, 228.8)/1000 person-years, respectively). Compared to the respective FDS subgroup without diabetes/schizophrenia, the mortality rate ratio was approximately 50% higher in the type 2 diabetes subgroup, and three times higher in those with type 2 diabetes/schizophrenia. In Cox regression, unadjusted hazard ratios were highest in those with type 2 diabetes/schizophrenia in FDS1 (HR (95% CI): 3.71 (1.54, 8.93) and FDS2 (2.96 (1.11, 7.91)), increasing to 5.61 (2.33, 13.5) and 26.9 (9.94, 72.6), respectively, after adjustment for age.

Although limited by small numbers of schizophrenia cases, these data suggest that comorbid type 2 diabetes and schizophrenia remains associated with a substantial and possibly increasing mortality gap.