For people who develop Alzheimer’s disease dementia, cognitive impairment may begin even earlier in the preclinical stage than previously thought, according to a study published in Neurology.
Performance on cognitive tests of episodic memory, executive function, and global cognition predicted the development of Alzheimer’s disease dementia up to 18 years before disease development.
The study included 2,125 participants aged 65 years and older from four neighborhoods in Chicago. Participants were stratified into six groups based on time before Alzheimer’s disease dementia diagnosis: 0.1-0.9 years, 1.0-3.9 years, 4.0-6.9 years, 7.0-9.9 years, 10.0-12.9 years, and 13.0-17.9 years. All participants completed a composite cognitive test score based on tests of episodic memory, executive function, and global cognition.
Over a follow-up period of 18 years, 442 (21%) of participants developed clinical Alzheimer’s disease dementia. Participants who had lower composite cognitive test scores were more likely to develop dementia over the course of the study. The association between cognitive test scores and dementia development had an odds ratio of 3.39 for the 13.0-17.9 years group. For the 0.1-0.9 years group, the odds ratio rose to 9.84. The researchers found that the associations were larger among European Americans than African Americans.
These findings indicate that cognitive impairment may appear even earlier than previously thought among people who will eventually develop dementia.
Objective: To examine the relation of performance on brief cognitive tests to development of clinically diagnosed Alzheimer disease (AD) dementia over the following 18 years in a sample of African Americans and European Americans.
Methods: A composite cognitive test score based on tests of episodic memory, executive function, and global cognition was constructed in a prospective population-based sample of 2,125 participants (55% African American and 61% female) aged 65 years and older residing in 4 Chicago neighborhoods. Time before AD dementia diagnosis was categorized into 6 groups corresponding to data collection periods: 0.1–0.9, 1.0–3.9, 4.0–6.9, 7.0–9.9, 10.0–12.9, and 13.0–17.9 years.