Glycemic Control, Complications, and Death in Older Diabetic Patients

OBJECTIVE To identify the range of glycemic levels associated with the lowest rates of complications and mortality in older diabetic patients. RESEARCH DESIGN AND METHODS We conducted a retrospective cohort study (2004-2008) of 71,092 patients with type 2 diabetes, aged ≥60 years, enrolled in Kaiser Permanente Northern California. We specified Cox proportional hazards models to evaluate the relationships between baseline glycated hemoglobin (A1C) and subsequent outcomes (nonfatal complications [acute metabolic, microvascular, and cardiovascular events] and mortality). RESULTS The cohort (aged 71.0 ± 7.4 years [means ± SD]) had a mean A1C of 7.0 ± 1.2%. The risk of any nonfatal complication rose monotonically for levels of A1C >6.0% (e.g., adjusted hazard ratio 1.09 [95% CI 1.02-1.16] for A1C 6.0-6.9% and 1.86 [1.63-2.13] for A1C ≥11.0%). Mortality had a U-shaped relationship with A1C. Compared with the risk with A1C <6.0%, mortality risk was lower for A1C levels between 6.0 and 9.0% (e.g., 0.83 [0.76-0.90] for A1C 7.0-7.9%) and higher at A1C ≥11.0% (1.31 [1.09-1.57]). Risk of any end point (complication or death) became significantly higher at A1C ≥8.0%. Patterns generally were consistent across age-groups (60-69, 70-79, and ≥80 years). CONCLUSIONS Observed relationships between A1C and combined end points support setting a target of A1C <8.0% for older patients, with the caution that A1Cs <6.0% were associated with increased mortality risk. Additional research is needed to evaluate the low A1C-mortality relationship, as well as protocols for individualizing diabetes care.