Relationship between HbA_1c levels and risk of cardiovascular adverse outcomes and all-cause mortality in overweight and obese cardiovascular high-risk women and men with type 2 diabetes

The optimal HbA_1c concentration for prevention of macrovascular complications and deaths in obese cardiovascular high-risk patients with type 2 diabetes remains to be established and was therefore studied in this post hoc analysis of the Sibutramine Cardiovascular OUTcomes (SCOUT) trial, which enrolled overweight and obese patients with type 2 diabetes and/or cardiovascular disease.

HRs for meeting the primary endpoint (nonfatal myocardial infarction, nonfatal stroke, resuscitated cardiac arrest or cardiovascular death) and all-cause mortality were analysed using Cox regression models.

Of 8,252 patients with type 2 diabetes included in SCOUT, 7,479 had measurements of HbA_1c available at baseline (i.e. study randomisation). Median age was 62 years (range 51–86 years), median BMI was 34.0 kg/m² (24.8–65.1 kg/m²) and 44% were women. The median HbA_1c concentration was 7.2% (3.8–15.9%) (55 mmol/l [18–150 mmol/l]) and median diabetes duration was 7 years (0–57 years). For each 1 percentage point HbA_1c increase, the adjusted HR for the primary endpoint was 1.17 (95% CI 1.11, 1.23); no differential sex effect was observed (p = 0.12 for interaction). In contrast, the risk of all-cause mortality was found to be greater in women than in men: HR 1.22 (1.10, 1.34) vs 1.12 (1.04, 1.20) for each 1 percentage point HbA_1c increase (p = 0.02 for interaction). There was no evidence of increased risk associated with HbA_1c ≤6.4% (≤46 mmol/l). Glucose-lowering treatment regimens, diabetes duration or a history of cardiovascular disease did not modify the associations.

In overweight, cardiovascular high-risk patients with type 2 diabetes, increasing HbA_1c concentrations were associated with increasing risks of cardiovascular adverse outcomes and all-cause mortality.