Rurality, type 2 diabetes and risk of cardiovascular events in Alberta, Canada: a retrospective cohort study

OBJECTIVE: To describe the association between place of residence in Alberta, Canada, and cardiovascular event risk among adults newly treated with metformin for type 2 diabetes. DESIGN: Retrospective cohort study. SETTING: Administrative data from Alberta, Canada between 2008 and 2023. PARTICIPANTS: Adult new metformin users, categorised by residence (rural, urban, metropolitan) from postal codes 1 year before metformin. PRIMARY AND SECONDARY OUTCOME MEASURES: Cause-specific hazard models were constructed for the primary composite outcome (cardiovascular mortality, hospitalisation for an acute coronary syndrome or stroke) and each of the secondary outcomes (components of the primary outcome and all-cause mortality). Models were adjusted for baseline demographics, healthcare utilisation and diabetes complications. RESULTS: A total of 236 005 adult new metformin users were identified and distributed across the rural-urban continuum (66% metropolitan, 10% urban, 24% rural). Mean age was 55 years, 55% were men, and mean follow-up time was 5.7 years. There were 19 059 primary composite outcome events, and rural residents were more likely to experience the outcome, adjusted HR (aHR): 1.09 (95% CI 1.06 to 1.13), compared with metropolitan. A significant interaction between residence and cardiovascular event history was identified. When stratified, risk of the primary outcome among those without cardiovascular history and living in a rural area was aHR: 1.16 (95% CI 1.11 to 1.20). Among rural residents with cardiovascular history, the risk was aHR: 0.84 (95% CI 0.78 to 0.91). CONCLUSIONS: Quantifying the association between residence and risk of cardiovascular events may focus the allocation of healthcare resources. Development of targeted intervention programmes should focus on primary prevention in rural areas and secondary prevention in metropolitan areas.