Normal ageing, impaired cognitive function, and senile dementia of the Alzheimer's type: a continuum?

There is little evidence to support the view that senile dementia of the Alzheimer's type (SDAT) is distinct from the normal ageing process. The changes in brain function found in normal ageing, benign senescent forgetfulness, and SDAT can be seen as a continuum, which may reflect a single underlying process. The failure to account for this possibility in research design may explain why few risk factors for SDAT have been identified.