Age of Diabetes Diagnosis and Lifetime Risk of Dementia: The Atherosclerosis Risk in Communities (ARIC) Study

OBJECTIVE The impact of age of diabetes diagnosis on dementia risk across the life course is poorly characterized. We estimated the lifetime risk of dementia by age of diabetes diagnosis. RESEARCH DESIGN AND METHODS We included 13,087 participants from the Atherosclerosis Risk in Communities Study who were free from dementia at age 60 years. We categorized participants as having middle age–onset diabetes (diagnosis <60 years), older-onset diabetes (diagnosis 60–69 years), or no diabetes. Incident dementia was ascertained via adjudication and active surveillance. We used the cumulative incidence function estimator to characterize the lifetime risk of dementia by age of diabetes diagnosis while accounting for the competing risk of mortality. We used restricted mean survival time to calculate years lived without and with dementia. RESULTS Among 13,087 participants, there were 2,982 individuals with dementia and 4,662 deaths without dementia during a median follow-up of 24.1 (percentile 25–percentile 75, 17.4–28.3) years. Individuals with middle age–onset diabetes had a significantly higher lifetime risk of dementia than those with older-onset diabetes (36.0% vs. 31.0%). Compared with those with no diabetes, participants with middle age–onset diabetes also had a higher cumulative incidence of dementia by age 80 years (16.1% vs. 9.4%), but a lower lifetime risk (36.0% vs. 45.6%) due to shorter survival. Individuals with middle age–onset diabetes developed dementia 4 and 1 years earlier than those without diabetes and those with older-onset diabetes, respectively. CONCLUSIONS Preventing or delaying diabetes may be an important approach for reducing dementia risk throughout the life course.