Hemoglobin A1C levels below 6% are associated with a small but significant increased risk of mortality in elderly patients. Overall outcomes are best when A1C levels are between 6% and 8%, according to a retrospective cohort study published online in Diabetes Care.
Investigators followed 71,092 patients with type 2 diabetes who were aged 60 years and older and were enrolled in Kaiser Permanente Northern California from 2004 to 2008. Relationships between baseline A1C level and nonfatal complications such as acute metabolic, microvascular, and cardiovascular events, and mortality were evaluated with Cox proportional hazards models to determine the range of A1C levels associated with the lowest complications and mortality rates.
The study demonstrated that the risk of any nonfatal complication rose monotonically for levels of A1C >6% (eg, adjusted HR=1.09; 95% CI, 1.02–1.16] for A1C 6.0% to 6.9% and 1.86 [1.63–2.13] for A1C ≥11.0%). Mortality risk was higher with A1C levels below 6% and ≥11% (1.31 [1.09–1.57]). The risk of both nonfatal complications and mortality rose significantly with A1C levels ≥8.0%. The best overall outcomes were among those with A1C levels >6% but below 8%. Investigators observed similar patterns across age groups (aged 60 to 69, 70 to 79, and ≥80 years).
"We cannot say whether this unexpected finding is due to the very low blood sugar itself, the treatments used to control blood sugars, or to some other factors not directly related to the care of diabetes," Study Co-author Andrew J. Karter, PhD, and the study's principal investigator at the Kaiser Permanente Division of Research, Oakland, Calif., said in a University of Chicago Medical Center press release. "It may be that the sickest patients at high risk of dying simply had low blood sugars to start with, rather than anything directly associated with the care of diabetes increasing the risk of death. Further research will be focused on identifying the mechanisms that underlie the somewhat increased mortality among those with very low A1c," he added.