What causes Alzheimer’s?

We do not yet fully understand what causes Alzheimer’s disease, but it is clear that it develops as the result of a complex series of events that take place in the brain over a long period of time. It is likely that the causes include genetic, environmental, and lifestyle factors.

One of the great mysteries of Alzheimer’s disease is why it largely strikes older adults. Research on how the brain changes normally with age is shedding light on this question. For example, scientists are learning how age-related changes in the brain may harm neurons and contribute to AD damage. These age-related changes include inflammation and the production of unstable molecules called free radicals.

Essentially, ever person with Alzheimer’s disease has accumulations of plaques and tangles in the brain.  Scientists are conducting studies to learn more about plaques, tangles, and other features of Alzheimer’s disease.  New technology has made it possible for researchers to visualize plaques and tangles by imaging the brains of living individuals. Findings from these studies may help researchers and clinicians better understand the causes of AD.


In a very few families, individuals develop AD in their 30s, 40s, and 50s. These individuals have a mutation, or permanent change, in one of three genes that they inherited from a parent. These mutations are autosomal dominant, meaning that inheriting the gene causes the disease.  Thus, the children of individuals with autosomal dominant Alzheimer’s disease (ADAD) are at 50% risk to inherit the mutation.  Only people who had a parent with ADAD are at risk to get this genetic form of the disease.  ADAD accounts for only 1-2% of all cases.

The “late-onset” form of the disease develops after age 60. Many genes have been identified that appear to affect risk for the disease.  The strongest of these is the apolipoprotein E (APOE) gene. The APOE gene has three forms: APOE e2, APOE e3, and APOE e4.  Carrying one or two copies of APOE e4 increases a person’s risk of getting Alzheimer’s disease. Carrying APOE e4, however, does not necessarily mean that a person will develop Alzheimer’s disease.  Also, people who carry only APOE e2 and/or e3 can and do develop AD.

Large-scale genetic research studies are searching for other genes  that increase or decrease susceptibility to Alzheimer’s disease. For more about this area of research, see the Alzheimer’s Disease Genetics Fact Sheet.

Lifestyle factors

A nutritious diet, exercise, social engagement, and mentally stimulating pursuits can all help people stay healthy. New research suggests that such healthy lifestyle choice also might reduce the risk of cognitive decline and Alzheimer’s disease. Scientists are investigating associations between cognitive decline and heart disease, high blood pressure, cholesterol, diabetes, and obesity, as well as lifestyle practices. Understanding these relationships and testing them in clinical trials will help clarify the extent to which controlling chronic health conditions and adopting healthy lifestyle practices may lessen the incidence of Alzheimer’s disease.