Incidence and lifetime risk of dementia and Alzheimer's disease in a Southern European population

Objective: To calculate both the incidence rates and the lifetime risk (LTR) of dementia and Alzheimer's disease (AD).

Methods: A two-phase case-finding procedure was implemented in a cohort of 4057 cognitively intact individuals 55+ years of age living in Zaragoza, Spain, and followed-up at 2.5 and 4.5 years. Age- and sex-specific incidence rates were calculated. A mortality-adjusted, multivariate model was used to document LTRs.

Results: The incidence rate of dementia continued to rise after the age of 90 years, but was slightly lower than in North and West European studies. Only a tendency for an increased LTR with age was observed. Thus, LTR was 19.7% for a 65-year-old woman and 20.4% at the age of 85 years, the corresponding figures for AD being 16.7% and 17.6%. The LTR of AD was higher in women and was about twice as high among illiterate individuals when compared with individuals with higher educational levels.

Conclusions: The incidence rate of dementia in this Southern European city was slightly lower than in previous studies in North-West Europe. LTR of dementia and AD seems to be slightly increased with age. The association of illiteracy with higher LTR of AD is intriguing.