Objective: To estimate the prevalence of dementia and its subtypes in the general population and examine the relation of the disease to education.
Design: Population based cross sectional study.
Setting: Ommoord, a suburb of Rotterdam.
Subjects: 7528 participants of the Rotterdam study aged 55-106 years.
Results: 474 cases of dementia were detected, giving an overall prevalence of 6.3%. Prevalence ranged from 0.4% (5/1181 subjects) at age 55-59 years to 43.2% (19/44) at 95 years and over. Alzheimer's disease was the main subdiagnosis (339 cases; 72%); it was also the main cause of the pronounced increase in dementia with age. The relative proportion of vascular dementia (76 cases; 16%), Parkinson's disease dementia (30; 6%), and other dementias (24; 5%) decreased with age. A substantially higher prevalence of dementia was found in subjects with a low level of education. The association with education was not due to confounding by cardiovascular disease.
Conclusions: The prevalence of dementia increases exponentially with age. About one third of the population aged 85 and over has dementia. Three quarters of all dementia is due to Alzheimer's disease. In this study an inverse dose-response relation was found between education and dementia--in particular, Alzheimer's disease.