Impact of diabetes control on mortality by race in a national cohort of veterans

Purpose: The association between glycated hemoglobin (HbA1c), medication use/adherence, and mortality stratified by race/ethnicity was examined in a national cohort of veterans with type 2 diabetes. Methods: A total of 892,223 veterans with diabetes in 2002 were followed through 2006. HbA1c category was the main exposure (i.e., HbA1c <7%, HbA1c 7%-8% [reference], HbA1c 8%-9%, and HbA1c >9%). Covariates included age, sex, marital status, rural/urban residence, geographic region, number of comorbidities, and diabetes medication use/adherence (i.e., adherent, medication possession ratio ≥80%; nonadherent; and nonusers). HbA1c and medication use/adherence varied over time, and Cox regression models accounting for time-varying variables were used. Results: In nonmedication users, HbA1c greater than 9% predicted higher mortality risk relative to HbA1c of 7%-8% in non-Hispanic whites (hazard ratio [HR], 1.55; 95% confidence interval [95% CI], 1.43-1.69), non-Hispanic blacks (NHB) (HR, 1.58; 95% CI, 1.34-1.87), and Hispanics (HR, 2.22; 95% CI, 1.75-2.82). In contrast, in nonadherent medication users, HbA1c less than 7% predicted higher mortality risk in NHB (HR, 1.12; 95% CI, 1.05-1.20), whereas HbA1c greater than 9% only predicted mortality in non-Hispanic whites (HR, 1.11; 95% CI, 1.06-1.16). In adherent medication users, HbA1c less than 7% predicted higher mortality in NHB (HR, 1.18; 95% CI, 1.07-1.31), whereas HbA1c greater than 9.0% predicted higher mortality risk across all race/ethnic groups. Conclusion: We found evidence for racial/ethnic differences in the association between glycemic control and mortality, which varied by medication use/adherence.