Mortality disparity by socioeconomic position in people with and without diabetes: open cohort studies in four high-income countries

There have been mixed findings on whether mortality is socially patterned among people with diabetes. We compared all-cause mortality trends by socioeconomic position (SEP) among people with and without diabetes for 2004-21 in four high-income countries. We conducted open cohort studies in Australia, Denmark, the Netherlands, and Scotland and included national or regional populations aged 35-69 years. We used the European standard population in 2013 to calculate age-standardized mortality rates (ASMRs) by calendar year, SEP quintile, diabetes status, and sex. SEP quintiles were defined using standardized disposable household income in Denmark and the Netherlands, and area-based indices in Australia and Scotland. We calculated the age-standardized slope index of inequality and age-adjusted relative index of inequality using Poisson regression as absolute and relative measures of socioeconomic inequality, respectively across the study populations stratified by calendar year, diabetes status, and sex. About 208 011 deaths occurred during 17 million person years (py) of follow-up among 35- to 69-year olds with diabetes, and 1.1 million deaths during 298 million py of follow-up among people without diabetes. ASMRs generally increased with increasing deprivation and varied between 1.3 (95% CI: 1.2-1.4) deaths per 1000 py to 29.4 (95% CI: 26.0-32.8) deaths per 1000 py. We found absolute and relative mortality inequality that increased during the follow-up period among adults without diabetes. Measures of absolute and relative inequality among adults with diabetes widened in some populations by country and sex. To conclude, disparities in mortality by SEP increased during follow-up in most countries. Strategies are needed to reduce excess mortality associated with low SEP and diabetes and related socioeconomic inequality.