Incidence of dementia: does gender make a difference?
Introduction
Dementia is one of the major health problems in our aging societies. Therefore, reliable estimates of the frequency of dementia are important. Incidence studies have reported inconsistent results on the occurrence of dementia by gender. Some studies suggested a higher incidence rate in women than in men, especially after age 85 [3], [5], [6], [12], [20], [27], whereas other studies showed no gender difference [4], [13], [17], [23], [24]. As to Alzheimer’s disease, dementia’s major subtype, most studies reported higher incidence rates for women than for men [5], [12], [14], [17]. The discrepancies between the various studies may result from small sample size, particularly in the highest age range, use of different diagnostic criteria and differences in completeness of follow-up.
We previously reported incidence data from the Rotterdam Study, a large population-based study conducted in the Netherlands, after a relatively short follow-up of on average two years. We now have more than 40,000 person years of follow-up and were able to investigate possible gender differences in incidence of dementia and its subtypes.
Section snippets
Study design
The Rotterdam Study is a population-based prospective cohort study among 7,983 persons aged 55 years and older [16]. Baseline examinations took place between 1990 and 1993. Participants were interviewed at their homes and thereafter, during two sessions, examined at the research center. Follow-up examinations took place in 1993–1994 (first follow-up) and in 1997–1999 (second follow-up).
Study population
The study was conducted in Ommoord, a suburb of the city of Rotterdam, the Netherlands. At baseline, all
Results
In Table 1 characteristics of the study population are summarized. Of the total cohort (n = 7,046) at risk of developing dementia, 1,403 persons (19.9%) died during follow-up. For the second follow-up examination 48 persons who had moved to a nursing home far from the research center were not invited and for those information was obtained through general practitioners. Follow up was virtually complete (99.6%) until December 31, 1999 (complete information during the first follow-up period, 26
Discussion
We assessed the incidence of dementia in a large population based ongoing cohort study and examined subtypes of dementia and differences between men and women. Up to age 90 we found no gender difference in dementia incidence, whereas above that age men seemed to be at lower risk than women. The overall incidence of Alzheimer’s disease was similar in men and women. Over the age of 90 years the incidence of Alzheimer’s disease was higher for women than for men. The risk of vascular dementia was
Acknowledgements
The Rotterdam Study was supported by the NESTOR stimulation program for geriatric research in the Netherlands (Ministry of Health, Welfare and Sports, and Ministry of Education, Science and Culture), the Netherlands Organization for Scientific Research (NWO), the Health Research Development Council and the municipality of Rotterdam. Dr M.M.B. Breteler is a fellow of the Royal Netherlands Academy of Arts and Sciences and supported by Alzheimer’s Association grant nr IIRG-99-1534.
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