Higher hemoglobin A1c levels were found to be associated with increased cardiovascular disease (CVD) risk among adult patients with diabetes, and this link was more pronounced among Black adults at increased levels of residential racial segregation, according to study findings published in Diabetes Care.

The current study was designed to assess whether the association between higher A1c levels and CVD risk among adults with and without diabetes was modified by residential racial segregation.

Using a case-cohort design, the researchers included a random baseline sample of 2136 participants and 1248 participants with incident CVD (coronary heart disease [CHD], fatal CHD during 7-year follow-up, and stroke) selected from 30,239 study participants originally assessed between 2003 and 2007 to participate in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. Cox proportional hazards models were used to assess the association between A1c and incident CVD, stratified by diabetes status at baseline and adjusted for CVD risk factors, demographics, and socioeconomic status. Interaction terms were used to assess effect modification by census tract-level residential segregation indices (dissimilarity, interaction, and isolation).

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Mean participant age in the random sample was 64.2±9.1 years (44% Black; 59% women; and 19% with diabetes). Levels of A1c were not associated with CVD risk among participants without diabetes; hazard ratio [HR] associated with each 1% [11 mmol/mol] increase in A1c was 0.94 (95% CI, 0.76-1.16) in the fully adjusted multivariable models. However, among patients with diabetes, A1c was associated with a 23% increased risk for CVD (HR, 1.23; 95% CI, 1.08-1.40). This association was modified by both the dissimilarity (P <.001) and interaction (P =.001) indices.

Risk for CVD increased at A1c levels between 7% and 9% (53-75 mmol/mol) for those living in areas with higher residential segregation (ie, lower interaction index). In race-stratified analyses, residential segregation had a more pronounced modifying effect among Black participants with diabetes; however, only a modest effect among White participants was noted.

Study researchers concluded, “Higher A1c increased the risk [for] CVD among those with diabetes but not those without diabetes. Among those with diabetes, living in areas with higher segregation, as measured by the interaction index, appeared to modestly but significantly modify this risk relationship…” However, they noted, “Additional research on how structural determinants may modify health effects is needed.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Cummings DM, Patil SP, Long DL, et al. Does the association between hemoglobin A1c and risk of cardiovascular events vary by residential segregation? The REasons for Geographic And Racial Differences in Stroke (REGARDS) study. Diabetes Care. 2021;44:1-8. doi:10.2337/dc20-1710