Health inequality in eight adverse outcomes over a 25-year period in a multi-ethnic population in New Zealand population with impaired glucose tolerance and/or impaired fasting glucose : an age-period-cohort analysis

Purpose: We aimed to examine socioeconomic inequality (SI) in cause-specific outcomes among adults with impaired glucose tolerance (IGT) and/or Impaired fasting glucose (IFG) in New Zealand (NZ) over 25 years. Patients and Methods: A population-based open cohort was derived from Diabetes Care Support Service in NZ with national databases linkage. Patients aged ≥18 years with IGT and/or IFG were enrolled between 01/01/1994 and 31/07/2018 and followed up until death or 31/12/2018. Incident outcomes (all-cause, premature, cardiovascular, and cancer death; cardiovascular, myocardial infarction, stroke, heart failure, and end-stage kidney disease hospitalization) by demographic, anthropometric, socioeconomic status, clinical measurements, enrol-time-periods, and IGT/IFG were evaluated. Adjusted incidence rate ratios, absolute risk difference, and SI measurements (slope and relative index of inequality) were estimated using Age-Period-Cohort models. Results: 29,894 patients (58.5 (SD 14.3) years mean age; 52.2% female) were enrolled with 5.6 (IQR: 4.4–7.4) years of median follow-up. Mortality rates decreased, whereas hospitalization (except myocardial infarction) rates increased. SI was significant for each outcome. Higher mortality and hospitalization rates and worsened SI were common in men, older, the most deprived, and Māori patients, as well as patients with obesity, current smoking, with both IFG and IGT, and greater metabolic derangement (higher systolic blood pressure, lipids, and HbA1c, and lower level of mean arterial pressure). Conclusion: Enhanced management strategies are necessary for people with IGT and/or IFG to address persisting SI, especially for men, older people, current smokers, NZ European and Māori patients, patients with obesity, or with any abnormal metabolic measurements.