Although Alzheimer's disease (AD) is a primary degenerative brain disease with unknown etiology, its pathogenesis is related to the effect of reduced estrogen levels on brain structure and function. Alzheimer's disease has characteristic neuropathological and neurochemical changes. It often has an insidious onset, develops slowly and steadily over a period of several years, and usually results in death 6 to 12 years after onset. In 1907, Alzheimer first reported a case of dementia in a woman in her 50s and named it Alzheimer disease, AD, or early dementia. Another type of dementia with a later onset was once called senile dementia. In recent years, people have realized that the neuropathological changes of these two diseases are the same, so they can be regarded as the same disease.