Prevalence of Alzheimer's disease in a community population of older persons. Higher than previously reported.
Level 4 - case-series / case-control
Cross-sectional community-based prevalence survey with stratified sampling
What was done
In a geographically defined US community, 3,623 residents over 65 years of age (80.8% of all eligible residents) underwent brief in-home memory screening. A stratified sample of 467 individuals then received comprehensive neurological, neuropsychological, and laboratory examinations to identify clinically diagnosed Alzheimer's disease and other dementias. Population prevalence rates were projected from the clinically evaluated sample to the broader community population.
What was found
An estimated 10.3% (95% CI, 8.1% to 12.5%) of community residents over age 65 had probable Alzheimer's disease. Prevalence rates rose sharply with advancing age: 3.0% (95% CI, 0.8% to 5.2%) in individuals aged 65 to 74; 18.7% (95% CI, 13.2% to 24.2%) in those aged 75 to 84; and 47.2% (95% CI, 37.0% to 63.2%) in those aged 85 and older. Clinically diagnosed Alzheimer's disease accounted for 84.1% of all cases of moderate or severe cognitive impairment, while other dementing illnesses were uncommon.
Why it matters
This study provided landmark community-based epidemiological evidence indicating that Alzheimer's disease was far more prevalent than previously recognized, particularly among adults over 85 years old.
Limits
The study was restricted to a single geographically defined US community, which may limit generalizability. Comprehensive clinical diagnostic evaluations were performed in a stratified subset of 467 individuals rather than the full screened population of 3,623, requiring mathematical projection. Diagnoses were based on clinical criteria without neuropathological or biomarker verification.
Cited by
- supports Between 40% and 50% of adults in the United States who live to age 85 will receive a diagnosis of Alzheimer's disease.