Very old women at highest risk of dementia and Alzheimer's disease: Incidence data from the Kungsholmen project, Stockholm

Objective: To determine the incidence of different types of dementia in the very old, and to explore the relation with age and gender. Design: A dementia-free cohort was followed for an average of three years in Stockholm, Sweden. At the end of the follow-up, the subjects were interviewed by nurses, clinically examined by physicians, and cognitively assessed by psychologists. Deceased cohort members were studied using death certificates, hospital clinical records, and discharge diagnoses. Dementia diagnoses were made according to the DSM-III-R criteria independently by two physicians. Participants: The cohort consisted of 1,473 subjects (75+ years old), of which 987 were clinically examined at follow-up, 314 died before the examination, and 172 refused to participate. Results: During the follow-up, 148 subjects developed dementia. In the age-group 75 to 79, the incidence rates for dementia were 19.6 for women and 12.4 for men per 1,000 person-years, whereas for 90+ year-old subjects the corresponding figures were 86.7 and 15.0 per 1,000 person-years. A similar pattern of distribution by age and gender was seen for Alzheimer's disease. In each age stratum, the incidence rates of dementia and Alzheimer's disease were higher for women than for men. The age-adjusted odds ratio for women was 1.9 for dementia and 3.1 for Alzheimer's disease. Conclusions: (1) The incidence of dementia increases with age, even in the oldest age groups; (2) women have a higher risk of developing dementia than men, especially at very old ages; (3) this pattern is mainly due to the age and gender distribution of Alzheimer's disease, rather than vascular dementia.