Glycated haemoglobin and cardiovascular outcomes in people with Type 2 diabetes: a large prospective cohort study

Aims To investigate the association between long-term glycaemic control, measured by glycated haemoglobin (HbA(1c)), and time to first cardiovascular disease (CVD) event for people with Type 2 diabetes in New Zealand. Methods A prospective cohort study including people with Type 2 diabetes but no previous CVD. The primary outcome measure was time to first recorded fatal or non-fatal CVD event (ischaemic heart disease, cerebrovascular accident, transient ischaemic attack or peripheral vascular disease) as identified from linked primary care, hospital and mortality records between January 2000 and December 2005. A Cox proportional hazards model was used to examine the association between HbA(1c) and time to CVD event, adjusting for age at diagnosis, duration of diabetes, gender, ethnicity, socioeconomic status, smoking, blood pressure (BP), serum total cholesterol : high-density lipoprotein ratio, body mass index (BMI) and urine albumin : creatinine ratio. Results Participants included 48 444 people with Type 2 diabetes. Fifty-one per cent (n = 24 721) were women, median age 60 years. Median duration of diabetes was 3 years, median BMI 31 kg/m(2), median HbA(1c) 7.1% and mean BP was 138/81 mmHg. During the study period (median follow-up 2.4 years), there were 5667 first CVD events (11.7% of cohort). Each 1% increase in HbA(1c) was associated with an increase in hazard ratio (HR) for CVD of 1.08 (95% confidence interval 1.06-1.10, P < 0.001), myocardial infarction [HR 1.08 (1.04, 1.11)] and stroke [HR 1.09 ( 1.04, 1.13)]. Conclusion This study has confirmed in a large prospective cohort that increased HbA(1c) is an independent risk factor for cardiovascular disease after controlling for traditional risk factors.