Glycated hemoglobin and all-cause and cause-specific mortality among adults with and without diabetes.

CONTEXT: The patterns of associations between glycated hemoglobin (HbA1c) and mortality are still unclear.

OBJECTIVE: To explore the extent to which ranges of HbA1c levels are associated with the risk of mortality among participants with and without diabetes.

DESIGN: Setting and patients: This was a nationwide, community-based prospective cohort study. Included were 15,869 participants (median age 64 years) of the Health and Retirement Study, with available HbA1c data and without a history of cancer. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) with 95% confidential intervals (95% CIs) for mortality.

RESULTS: A total of 2,133 participants died during a median follow-up of 5.8 years. In participants with diabetes, those with an HbA1c level of 6.5% were at the lowest risk of all-cause mortality. When HbA1c level was lower than 5.6% or higher than 7.4%, the increased all-cause mortality risk became statistically significant as compared with an HbA1c level of 6.5%. As for participants without diabetes, those with an HbA1c level of 5.4% were at the lowest risk of all-cause mortality. When HbA1c level was lower than 5.0%, the increased all-cause mortality risk became statistically significant as compared with an HbA1c level of 5.4%. However, we did not observe a statistically significant elevated risk of all-cause mortality above an HbA1c level of 5.4%.

CONCLUSIONS: A U-shaped and a reverse J-shaped association for all-cause mortality were found among participants with and without diabetes. The corresponding Optimal ranges for overall survival are predicted to be 5.6-7.4% and 5.0-6.5%, respectively.