To examine the association between baseline HbA1c level and mortality attributable to all-cause, cardiovascular disease, coronary heart disease and stroke.Methods
A total of 2137 Chinese aged 65 years or above attending the Elderly Health Service, Department of Health, Hong Kong, with diagnosed diabetes had HbA1c 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 7.9 years of follow-up, 540 participants had died. After adjusting for potential confounders, higher HbA1c (≥ 69 mmol/mol, 8.5%) increased the risk of cardiovascular disease (hazard ratio 2.11;95% CI 1.37–3.25) and stroke mortality (hazard ratio 2.43; 95% CI 1.06–5.55) compared with HbA1c of 58–68 mmol/mol (7.5–8.4%), and increased the risk of all-cause (hazard ratio 1.41; 95% CI 1.06–1.86) and coronary heart disease mortality (hazard ratio 2.44; 95% CI 1.11–5.37) compared with HbA1c of 48 mmol/mol (6.5%) or less. Analysis of HbA1c as a continuous variable showed that every XX mmol/mol (1%) increase in HbA1c decreased stroke mortality risk by 51% in those with HbA1c level less than 48 mmol/mol (6.5%) and increased stroke mortality risk by 30% in those with an HbA1c level of 48 mmol/mol (6.5%) or higher, suggesting a U-shaped association between HbA1c and stroke mortality.Conclusion
High HbA1c predicted excess risk of all-cause, cardiovascular disease, coronary heart disease and stroke mortality. The question of whether low HbA1c increases mortality in older patients with diabetes needs further investigation.