Diabetes control: Incidence of acute myocardial infarction and all-cause mortality among patients with 3-6 years' disease duration

Background Optimal glycated haemoglobin (HbA1c) concentrations to minimize large vessel complications and prolong life in diabetes patients are not well established. Design A retrospective cohort study from 2010 to 2012 using data from the Clalit Health Service (Clalit) integrated healthcare system's electronic data warehouse. Patients included had newly incident diabetes, had at least two HbA1c measurements during the 3 years prior to 1 January 2010 without any disruption(s) in Clalit membership between 2010 and 2014. Methods Time-dependent variables were utilized for HbA1c concentration exposure at three time periods. Diabetes control was evaluated taking average HbA1c measures per time period. Unadjusted and adjusted extended Cox regression analyses assessed the association between time-dependent average HbA1c level and acute myocardial infarction and all-cause mortality. Results Among our 61,971 participants, 2.0% experienced acute myocardial infarction and 6.9% died. Compared to patients with HbA1c 7.0 to < 7.5%, a higher risk of myocardial infarction was found with 8.5 to < 9.0% (hazard ratio (HR) 1.42, 95% confidence interval (CI) 1.05-1.91) and ≥9.0% (HR 1.87, 95% CI 1.50-2.33) groups; a lower risk was found among <6.0% (HR 0.74, 95% CI 0.59-0.93), 6.0 to < 6.5% (HR 0.77, 95% CI 0.64-0.94) and 6.5 to < 7.0% (HR 0.73, 95% CI 0.60-0.88) groups. The association with all-cause mortality was J-shaped, demonstrating a higher risk in those <6.0% (HR 1.20, 95% CI 1.06-1.34), 7.5 to < 8.0% (HR 1.17, 95% CI 1.02-1.35), 8.0 to < 8.5% (HR 1.38, 95% CI 1.16-1.64), 8.5 to < 9.0% (HR 1.36, 95% CI 1.10-1.67) and ≥9.0% (HR 1.74, 95% CI 1.49-2.04) groups. Conclusions HbA1c concentration below 6.0% may be associated with an excess risk for all-cause mortality. Clinicians must be aware of this association when treating individual patients.