Aim/hypothesis  

HbA₁c concentrations are known to be associated with all-cause excess mortality risk in Caucasians. However, the relationship has not been clarified well in the Japanese. In addition, studies of the relationship between HbA₁c and mortality from malignant neoplasms are scarce.

Methods  

HbA₁c was measured for 3,710 people of a cohort composed of A-bomb survivors and controls. At baseline they were divided into five groups: a normal HbA₁c group of 1,143 individuals with HbA₁c of <5.5%, a slightly high but normal HbA₁c group of 1,341 individuals with HbA₁c 5.5% to <6.0%, a slightly high HbA₁c group of 589 individuals with HbA₁c 6.0% to <6.5%, a high HbA₁c group of 259 individuals with HbA₁c 6.5%, and a group of 378 individuals known to have type 2 diabetes. Using a Cox proportional hazards model, hazard ratios based on comparisons with the normal HbA₁c group were obtained.

Results  

During the observation period there were 754 deaths. For all-cause and cardiovascular disease mortality, a significant increase of the hazard ratio was observed for the slightly high HbA₁c group. A similar increase in malignant neoplasm-related mortality was observed for both the high HbA₁c group and the diabetes group.

Conclusions/interpretation  

Our results suggest that individuals in the Japanese population with HbA₁c levels of 6% or more might have increased mortality risk. The results indicate that HbA₁c measurements should be sought even for people who have not been diagnosed with diabetes.