Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study

Background: Type 2 diabetes affects Indigenous and non-European populations disproportionately, including in New Zealand, where long-term temporal trends in cause-specific clinical outcomes between Māori, Pacific, and European people remain unclear. We aimed to compare the rates of mortality and hospital admission between Māori, Pacific, and European patients with type 2 diabetes in Auckland, New Zealand, over a period of 24 years. Methods: In this retrospective, population-based, longitudinal cohort study, we identified a cohort of patients (aged 35–84 years) with type 2 diabetes enrolled between Jan 1, 1994, and July 31, 2018, to the primary care audit programme, the Diabetes Care Support Service (DCSS) in Auckland, New Zealand. Patients with type 1 diabetes, prediabetes, and gestational diabetes were excluded. We linked data from the DCSS with national death registration, hospital admission, pharmaceutical claim, and socioeconomic status databases. Patients were followed up until death or July 31, 2018 (date of last enrolment to the DCSS). Incident clinical events (all-cause mortality, cardiovascular mortality, cancer mortality, cardiovascular hospital admission, cancer hospital admission, and end-stage renal disease hospital admission) were identified. Event rates were stratified by ethnic group, age group, sex, socioeconomic status, and time period (<1998, 1999–2013, 2004–08, 2009–13, and 2014–18). Incidence rate ratios (IRRs) and absolute risk differences were adjusted for sex, age, smoking status, obesity, socioeconomic status, and time period by use of age-period-cohort modelling. Findings: Between Jan 1, 1994, and July 31, 2018, 45 072 patients with type 2 diabetes (21 936 [48·7%] female; mean age 56·7 years [SD 13·8]) were enrolled in the DCSS and followed up for a median of 9·7 years (IQR 5·8–13·6). 16 755 (37·2%) were European, 7093 (15·7%) were Māori, and 12 044 (26·7%) were Pacific patients. Despite a similar temporal trend (decreasing mortality and increasing hospital admissions) across the three ethnic groups, Māori and Pacific patients had consistently higher hospital admission rates than European patients. Māori but not Pacific patients had higher adjusted IRRs for all-cause mortality (1·96 [95% CI 1·80–2·14]), cardiovascular mortality (1·93 [1·63–2·29]) and cancer mortality (1·64 [1·40–1·93]) rates compared with European patients. Interpretation: Compared with European patients, poorer health outcomes have persisted among Māori and Pacific people with type 2 diabetes for more than 20 years. New policies supporting prevention and more intensive management of type 2 diabetes are urgently needed. Research into the biological and societal mechanisms underlying these disparities, and the associated differences between Māori and Pacific patients is also needed. Funding: Counties Manukau Health and Middlemore Foundation.