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 subu rb of Rotterdam, aged 55 years and older, Baseline examinations took p lace between 1990 and 1993. The average follow-up was 2.1 years. Scree ning for dementia followed a three-stage protocol. Medical records of subjects who had died or could not be examined in person were evaluate d, Of 7,046 subjects who were nondemented at baseline, 162 developed d ementia during 15,135 person-years of follow-up, resulting in an overa ll incidence rate of 10.7 per 1,000 person-years, From the youngest to the oldest Ei-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 o ff after age 85. Overall, the incidence rate per 1,000 person-years wa s 7.7 for Alzheimer's disease and 1.5 for vascular dementia. Dementia incidence rates and dementia-free Kaplan-Meier survival tables were us ed to calculate age-and sex-specific cumulative risks of dementia, Alt hough 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.