Alzheimer’s disease is the most
common cause of dementia among
older people. Dementia is the loss of
cognitive functioning—thinking,
remembering, and reasoning—and
behavioral abilities, to such an extent
that it interferes with a person’s daily
life and activities. Dementia ranges
in severity from the mildest stage,
when it is just beginning to affect
a person’s functioning, to the most
severe stage, when the person must
depend completely on others for basic
activities of daily living.