Lifetime risk of dementia and Alzheimer's disease. The impact of mortality on risk estimates in the Framingham Study.
Level 3 - non-randomized controlled study
Prospective observational cohort study.
PubMed 9409336 · doi:10.1212/wnl.49.6.1498
What was done
A total of 2,611 cognitively intact participants (1,061 men, 1,550 women; mean age 66 ± 7 years) from the Framingham Study were prospectively followed over 20 years to monitor the development of Alzheimer's disease (AD) and all-cause dementia. Using a modified survival analysis that accounted for competing mortality risks, researchers calculated sex-specific remaining lifetime risks and standard cumulative incidence rates for 5-year age intervals beginning at age 65.
What was found
Over 20 years, 198 participants developed dementia, including 120 with AD. Remaining lifetime risk was higher in women and remained relatively stable between ages 65 and 80. For a 65-year-old man, the remaining lifetime risk was 6.3% (95% CI, 3.9 to 8.7) for AD and 10.9% (95% CI, 8.0 to 13.8) for all-cause dementia. For a 65-year-old woman, the corresponding risks were 12.0% (95% CI, 9.2 to 14.8) for AD and 19.0% (95% CI, 17.2 to 22.5) for dementia. Standard cumulative incidence from age 65 to 100 substantially overestimated risk compared to survival models accounting for mortality: 25.5% in men and 28.1% in women for AD, and 32.8% in men and 45.0% in women for dementia.
Why it matters
This study shows that conventional cumulative incidence substantially overstates lifetime dementia risk because it ignores competing mortality. Adjusting for life expectancy provides more realistic risk estimates for public health planning and clinical risk counseling.
Limits
The Framingham cohort consists predominantly of white, community-dwelling individuals in a single geographic region, limiting generalizability to diverse populations. The findings are based on 198 incident dementia cases observed over a 20-year period and reflect mortality and diagnostic patterns specific to that cohort's timeframe.
Cited by
- supports Women have approximately twice the risk of developing Alzheimer's disease compared to men.