No one knows yet exactly what causes Alzheimer’s disease. Researchers are learning about what happens to the brain as we grow older, what happens to brain cells in Alzheimer’s disease, what genes are associated with Alzheimer’s, and many other factors that may be important. Most researchers agree that the cause may be a complex set of factors.

Age and family history have been identified as potential risk factors. Studies have shown that the greatest known risk for developing Alzheimer’s is increasing age. As many as 10 percent of all people 65 years of age and older have Alzheimer’s. As many as 50 percent of all people 85 and older have the disease.

A small percentage of people in their 30’s, 40’s and 50’s get Alzheimer’s. This early onset form of Alzheimer’s accounts for less than 10 percent of all reported cases and is considered quite rare. Scientists believe this variation of the disease may be genetically transmitted across multiple generations of the same family. They have identified three genes that cause Early Onset Alzheimer’s. Investigations of these genes have provided important clues about the biology of Alzheimer's. Researchers have also identified one gene that raises the risk of the more common form of Alzheimer's that affects older people. However the evidence is not clear that Alzheimer’s that strikes people over 65 is hereditary.

Alzheimer's disease knows no social or economic boundaries. While it affects both sexes, it particularly affects women, most likely because women generally live longer than men.

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Much dementia research has focused on vascular risk factors, which are factors related to the blood circulation system. A great deal of evidence shows that disorders such as high cholesterol and high blood pressure — factors that cause strokes and heart disease — may also increase the risk for developing Alzheimer’s.

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