Incidence and risk of dementia. The Rotterdam Study

To assess age-, sex-, and subtype-specific incidence rates of dementia and to calculate the risk of dementia, the authors performed a large, community-based, prospective cohort study on dementia as part of the Rotterdam Study. Participants were recruited among residents of a suburb of Rotterdam, aged 55 years and older. Baseline examinations took place between 1990 and 1993. The average follow-up was 2.1 years. Screening for dementia followed a three-stage protocol. Medical records of subjects who had died or could not be examined in person were evaluated. Of 7,046 subjects who were nondemented at baseline, 162 developed dementia during 15,135 person-years of follow-up, resulting in an overall incidence rate of 10.7 per 1,000 person-years. From the youngest to the oldest 5-year age category, the incidence rate increased from 0.6 to 97.2 per 1,000 person-years. Only in men did the increase level off after age 85. Overall, the incidence rate per 1,000 person-years was 7.7 for Alzheimer's disease and 1.5 for vascular dementia. Dementia incidence rates and dementia-free Kaplan-Meier survival tables were used to calculate age- and sex-specific cumulative risks of dementia. Although the incidence rates of men and women up to age 85 were similar, the lifetime risk of dementia for 55-year-old women was twice as high as for men (0.33 vs. 0.16), reflecting both the higher life expectancy of women and the higher dementia risk at very old age.