Hemoglobin A_1c and Mortality in Older Adults With and Without Diabetes: Results From the National Health and Nutrition Examination Surveys (1988–2011)

OBJECTIVE Hemoglobin A_1c (HbA_1c) level has been associated with increased mortality in middle-aged populations. The optimal intensity of glucose control in older adults with diabetes remains uncertain. We sought to estimate the risk of mortality by HbA_1c levels among older adults with and without diabetes.

RESEARCH DESIGN AND METHODS We analyzed data from adults aged ≥65 years (n = 7,333) from the Third National Health and Nutrition Examination Survey (NHANES III) (1998–1994) and Continuous NHANES (1999–2004) and their linked mortality data (through December 2011). Cox proportional hazards models were used to examine the relationship of HbA_1c with the risk of all-cause and cause-specific (cardiovascular disease [CVD], cancer, and non-CVD/noncancer) mortality, separately for adults with diabetes and without diabetes.

RESULTS Over a median follow-up of 8.9 years, 4,729 participants died (1,262 from CVD, 850 from cancer, and 2,617 from non-CVD/noncancer causes). Compared with those with diagnosed diabetes and an HbA_1c <6.5%, the hazard ratio (HR) for all-cause mortality was significantly greater for adults with diabetes with an HbA_1c >8.0%. HRs were 1.6 (95% CI 1.02, 2.6) and 1.8 (95% CI 1.3, 2.6) for HbA_1c 8.0–8.9% and ≥9.0%, respectively (P for trend <0.001). Participants with undiagnosed diabetes and HbA_1c >6.5% had a 1.3 (95% CI 1.03, 1.8) times greater risk of all-cause mortality compared with participants without diabetes and HbA_1c 5.0–5.6%.

CONCLUSIONS An HbA_1c >8.0% was associated with increased risk of all-cause and cause-specific mortality in older adults with diabetes. Our results support the idea that better glycemic control is important for reducing mortality; however, in light of the conflicting evidence base, there is also a need for individualized glycemic targets for older adults with diabetes depending on their demographics, duration of diabetes, and existing comorbidities.