| The incidence of dementia increases sharply with age. The incidence at age 65 is roughly 1 per 1000 person-years, at age 75 1 per 100 person-years, and at the age of 95 reaches 1 per 10 person-years. Evidence is increasing that particularly in the very old the dementia syndrome usually results from a variety of causes that in combination bring out the clinical symptoms. Although the majority of patients gets clinically diagnosed with "Alzheimer's disease", post mortem studies suggest that mixed pathology is the rule rather than the exception. This is of particular relevance for the prevention of dementia in this age group. Given that in particular in the very old postponement of clinical onset of dementia will effectively result in prevention because of competing mortality, identification of modifiable risk factors is of prime interest. Vascular factors, endocrine factors, inflammation factors, dietary factors and lifestyle factors have all been associated with the risk of dementia and Alzheimer's disease in elderly populations. However, these have hardly been investigated in the very old. Most studies conducted thus far were underpowered to assess risk factors age-specifically, although several studies suggested that risk factors that may play a role at younger age are not important anymore if people have survived until higher ages. A possible explanation is that due to selective disease resistance and survival, the genetic mixture in the very old is considerably different from that in younger subjects. A larger population based study in the very old is needed to examine which potentially modifiable risk factors are associated with the risk of dementia in this high-risk group. We therefore propose to pool the data of two comparable population based studies to come up with a large enough sample of very old persons to address those important questions. |
