Type 2 Diabetes and 10-Year Risk of Dementia and Cognitive Impairment Among Older Mexican Americans

OBJECTIVE

Type 2 diabetes has been linked with increased risk of dementia and cognitive impairment among older adults and with premature mortality in young and middle-aged adults. No studies have evaluated the association between diabetes and dementia among Mexican Americans, a population with a high burden of diabetes. We evaluated the association of diabetes with incidence of dementia and cognitive impairment without dementia (CIND) among older Mexican Americans while accounting for competing risk from death.

RESEARCH DESIGN AND METHODS

This study included 1,617 participants 60–98 years of age from the Sacramento Area Latino Study on Aging followed up to 10 years from 1998. We evaluated the association between diabetes and dementia/CIND with competing risk regression models.

RESULTS

Participants free of dementia/CIND at baseline (n = 1,617) were followed annually up to 10 years. There were 677 (41.9%) participants with diabetes, 159 (9.8%) incident dementia/CIND cases, and 361 (22.3%) deaths. Treated and untreated diabetes (hazard ratio 2.12 [95% CI 1.65–2.73] and 2.15 [1.58–2.95]) and dementia/CIND (2.48 [1.75–3.51]) were associated with an increased risk of death. In models adjusted for competing risk of death, those with treated and untreated diabetes had an increased risk of dementia/CIND (2.05 [1.41–2.97] and 1.55 [0.93–2.58]) compared with those without diabetes.

CONCLUSIONS

These findings provide evidence that the association between type 2 diabetes and dementia/CIND among Mexican Americans remains strong after accounting for competing risk of mortality. Treatments that modify risk of death among those with diabetes may change future dementia risk.Type 2 diabetes is a common and established risk factor for vascular disease and mortality (1). Prevalence of type 2 diabetes is higher among older adults, and several minority racial/ethnic groups in the U.S. are disproportionally affected. Several prospective epidemiologic studies have found that older adults with type 2 diabetes have an approximately twofold increased risk of dementia (2–9), but others have not (10–13), and the mechanism is controversial (14,15). Possible mechanisms linking type 2 diabetes to dementia and cognitive impairment include chronic hyperglycemia or hypoglycemia, hyperinsulinemia or insulin resistance, effects of inflammatory cytokines and oxidative stress, and β-amyloid deposition in the brain (14,15). The type 2 diabetes–dementia association has not been evaluated among Mexican Americans, a population with a high prevalence of type 2 diabetes (16), poor glycemic control among those with diabetes (17), and higher rates of complications compared with non-Hispanic whites (18).Mortality occurs at younger ages among people with type 2 diabetes (19). Mortality rates are nearly twice as high among people with type 2 diabetes compared with people without diabetes (19–21). Cognitive decline is also associated with higher mortality rates (22,23). Premature death in those with diabetes may influence the risk of dementia or cognitive impairment associated with type 2 diabetes. Previous studies of the association between type 2 diabetes and dementia have not accounted for competing risk of death. In this paper, we evaluate the association between type 2 diabetes and incidence of dementia and cognitive impairment without dementia (CIND) in a cohort of older Mexican Americans followed for 10 years, accounting for the competing risk of death.