Page Outline
  1. Introduction
  2. Biology of Alzheimer’s disease
  3. Risk factors
  4. Paths to prevention
  5. More about the causes of Alzheimer’s


Alzheimer’s disease has no known single cause, but in the last 15 years scientists have learned a great deal about factors that may play a role.

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Biology of Alzheimer’s disease

Scientists believe that whatever triggers Alzheimer’s disease begins to damage the brain years before symptoms appear. When symptoms emerge, nerve cells that process, store and retrieve information have already begun to degenerate and die. Scientists regard two abnormal microscopic structures called "plaques" and "tangles" as Alzheimer hallmarks. Amyloid plaques (AM-uh-loyd plaks) are clumps of protein that accumulate outside the brain’s nerve cells. Tangles are twisted strands of another protein that form inside cells. Scientists do not yet know whether plaques or tangles cause Alzheimer’s or are a byproduct of some other process. Clinical trials of experimental drugs targeting amyloid are under way and should help clarify the role plaques play.

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Risk factors

Scientists have learned that Alzheimer’s disease involves the malfunction or death of nerve cells, but why this happens is still not known. However, they have identified certain risk factors that increase the likelihood of developing Alzheimer’s and discovered clues about possible strategies to reduce risk.


The greatest known risk factor is increasing age, and most individuals with the illness are 65 and older. The likelihood of developing Alzheimer’s approximately doubles every five years after age 65. After age 85, the risk reaches nearly 50 percent.

Family history and genetics

Another risk factor is family history. Research has shown that those who have a parent or sibling with Alzheimer’s are two to three times more likely to develop the disease than those who do not. The more individuals in a family who have the illness, the greater the risk.

Scientists have so far identified one gene that increases risk of Alzheimer’s but does not guarantee an individual will develop the disorder. Research has also revealed certain rare genes that virtually guarantee an individual will develop Alzheimer’s. The genes that directly cause the disease have been found in only a few hundred extended families worldwide and are thought to account for a tiny percentage of cases. Experts believe the vast majority of cases are caused by a complex combination of genetic and nongenetic influences.

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Paths to prevention

Genes and environment

Age, family history and genetics are all risk factors we can’t change. Scientists worldwide are looking for other risk factors that may provide opportunities for treatment or prevention. Some of our best information about the relative importance of risk factors we can and can’t control comes from studies of identical twins, who are the same age and have the same genes but have different life experiences.

Several twin studies have shown that when one twin develops Alzheimer’s, the other twin is at increased risk but does not always develop the disease. Other studies suggest that even in cases where both twins develop Alzheimer’s, the age where symptoms appear can differ significantly. These results suggest that even when there is a strong genetic influence, other factors can play a major role.

Head injury

Research is beginning to reveal clues about some potentially controllable risk factors. There appears to be a strong link between serious head injury and future risk of Alzheimer’s. It’s important to protect your head by buckling up your seat belt, wearing your helmet and fall-proofing your home.

Overall brain health

One promising line of research suggests that strategies for overall healthy aging may help keep the brain healthy and may even offer some protection against Alzheimer’s. These measures include eating a healthy diet, staying socially active, avoiding tobacco and excess alcohol, and exercising both body and mind.

Heart/head connection

Some of the strongest evidence links brain health to heart health. The risk of developing Alzheimer’s or vascular dementia appears to be increased by many conditions that damage the heart and blood vessels, including heart disease, diabetes, stroke and high blood pressure or cholesterol. You should work with your doctor to monitor your heart health and treat any problems that arise.

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More about the causes of Alzheimer’s

Read more about the causes of Alzheimer’s on our National Web Site.

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