Association between HbA1c and cardiovascular disease mortality in older Hong Kong Chinese with diabetes

Abstract

Objective To examine the association between baseline HbA 1c level and mortality attributable to all-cause, cardiovascular disease, coronary heart disease and stroke. Methods A total of 2137 Chinese aged 65years or above attending the Elderly Health Service, Department of Health, Hong Kong, with diagnosed diabetes had HbA 1c measured during 1998 to 2000 and were followed up to 2009. Information on socio-economic position, lifestyle factors and disease history was collected. Hazard ratios and 95% confidence intervals with adjustment for potential confounders were calculated using Cox's proportional hazards models. Results After an average of 7.9years of follow-up, 540 participants had died. After adjusting for potential confounders, higher HbA 1c (≥69mmol/mol, 8.5%) increased the risk of cardiovascular disease (hazard ratio2.11;95%CI 1.37-3.25) and stroke mortality (hazard ratio2.43; 95%CI 1.06-5.55) compared with HbA 1c of 58-68mmol/mol (7.5-8.4%), and increased the risk of all-cause (hazard ratio1.41; 95%CI 1.06-1.86) and coronary heart disease mortality (hazard ratio2.44; 95%CI 1.11-5.37) compared with HbA 1c of 48mmol/mol (6.5%) or less. Analysis of HbA 1c as a continuous variable showed that every XXmmol/mol (1%) increase in HbA 1c decreased stroke mortality risk by 51% in those with HbA 1c level less than 48mmol/mol (6.5%) and increased stroke mortality risk by 30% in those with an HbA 1c level of 48mmol/mol (6.5%) or higher, suggesting a U-shaped association between HbA 1c and stroke mortality. Conclusion High HbA 1c predicted excess risk of all-cause, cardiovascular disease, coronary heart disease and stroke mortality. The question of whether low HbA 1c increases mortality in older patients with diabetes needs further investigation. © 2011 The Authors. Diabetic Medicine © 2011 Diabetes UK.