Causes and Risk Factors of Alzheimer's Disease

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Scientists are still trying to fully understand the cause or causes of Alzheimer’s disease. While genetics are known to play a role, smoking, poor cardiovascular health, and other risk factors can too. Though research is still ongoing, it’s helpful to at least understand the hallmarks of Alzheimer’s—plaques and tangles—and what's known about increased likelihood of developing the disease.

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Common Causes

A distinct cause of Alzheimer's disease hasn't been identified. The current thinking is that it develops due to a combination of risk factors over time. These include genetic, lifestyle, and environmental risk factors.

Alzheimer's disease is characterized by a build-up of proteins in the brain. Though this cannot be measured in a living person, extensive autopsy studies have revealed this phenomenon. The build-up manifests in two ways:

  • Plaques: Deposits of the protein beta-amyloid that accumulate in the spaces between nerve cells
  • Tangles: Deposits of the protein tau that accumulate inside of nerve cells

Scientists are still studying how plaques and tangles are related to Alzheimer’s disease, but they somehow make it difficult for the cells to survive.

Autopsies have shown that most people develop some plaques and tangles as they age, but people with Alzheimer’s develop far more than those who do not develop the disease. Scientists still don’t know why some people develop so many compared to others, although several risk factors for Alzheimer’s disease have been uncovered.

Age

Advancing age is the number one risk factor for developing Alzheimer’s disease. It is estimated that one out of three people over the age of 85 has the disease.

Within the older population, Latinos have 1.5 times the risk as whites, while African Americans have twice the risk of whites. These groups also have a higher rate of cardiovascular disease compared to whites as well, which increases the risk of Alzheimer's disease.

The probability of being diagnosed with Alzheimer’s nearly doubles every five years after age 65.

Genetics

People who have a parent or sibling who developed Alzheimer’s are two to three times more likely to develop the disease than those with no such family history. If more than one close relative has been affected, the risk increases even more.

Scientists have identified two kinds of genes that are associated with this. The first, ApoE 4, is thought to be a risk gene that increases the likelihood of developing Alzheimer’s, but does not guarantee it. In addition to ApoE 4, scientists think there could be up to a dozen more risk genes yet to be discovered.

The second kind of gene is a deterministic gene, which is much rarer. Deterministic genes are only found in a few hundred extended families around the world. If a deterministic gene is inherited, the person will undoubtedly develop Alzheimer’s, probably at a much earlier age.

People with Down syndrome are more likely to develop Alzheimer's disease, and they develop it 10 to 20 years earlier than those without the condition. Down syndrome is caused by having three copies of chromosome 21, which has the beta-amyloid producing gene.

Cardiovascular

There is a strong link between heart health and brain health. Those who are free of heart disease or related conditions are at a lower risk of developing Alzheimer’s or another kind of dementia than those who have cardiovascular problems.

Conditions that damage the heart and blood vessels reduce the blood flow to the brain and the thinking is that this magnifies the cognitive problems that are caused by the buildup of the protein plaques and tangles. Coronary artery disease, atrial fibrillation, valve disease, and heart failure raise the risk of dementia.

Preventing or managing high blood pressure, high cholesterol, diabetes, and heart disease may lower your risk of Alzheimer's disease as all of these can lead to damage to the blood vessels or heart. High blood pressure raises your risk of cerebral infarcts, which can raise your risk for dementia.

There is some evidence that these conditions in and of themselves can raise your risk of dementia as well. When they are combined, it can greatly increase your risk. For example, having diabetes and other risk factors can raise your risk threefold.

A 2012 study found that people with mild cognitive impairment were more likely to progress to dementia if they had cardiovascular problems.

Lifestyle Risk Factors

Although age and family history are out of your control, several modifiable factors can influence your chances of developing Alzheimer’s disease.

A connection has been found between serious head injury and future development of Alzheimer’s, so those who practice safety measures such as wearing seat belts and not engaging in activities where there is a high risk of falling are at an advantage. As older people are more at risk of falls, check the home for tripping hazards and install safety equipment such as handrails where needed. And, of course, using safety equipment such as helmets when riding a bicycle, skiing, skateboarding, or playing sports is essential.

Evidence is mounting for the promotion of exercise and a healthy diet to reduce Alzheimer’s risk, as well as avoiding tobacco and limiting alcohol consumption. Poor sleep habits or sleep apnea that result in less deep sleep or daytime drowsiness may raise your risk as well.

Staying socially active and engaging in intellectually stimulating activities have been shown to have a protective effect against Alzheimer’s disease. Low education level (less than a high school education) has long been associated with increasing the risk of Alzheimer's disease.

Does Aluminum Cause Alzheimer's?

No, this is outdated speculation. The Alzheimer's Association reports that no studies have confirmed any connection between aluminum exposure and Alzheimer's, either as a cause of risk factor.


Frequently Asked Questions

What causes Alzheimer’s disease?

Scientists don’t fully know what causes Alzheimer’s disease but recognize that certain changes in the brain cause the progressive loss of neurons (nerve cells) and their connections. This is due in large part to the formation of lesions, called plaques, and twisted protein fibers, called tangles, in the brain.  These changes may be due to aging-related changes in the brain combined with genetic, environmental, and lifestyle factors the contribute to the onset of the disease.

What are the risk factors for Alzheimer’s disease?

Some of the risk factors for Alzheimer’s disease include:

  • Older age (most predominately 65 and over)
  • Family history of Alzheimer’s
  • Having the APOE-e4 gene (found in 40% to 65% of people with Alzheimer’s)
  • History of head trauma
  • Down syndrome

What are the early signs and symptoms of Alzheimer’s?

Alzheimer’s is characterized by the progressive loss of memory, cognition, judgment, reasoning, spatial awareness, communication, motor skills, and, eventually, the ability to live independently. Symptoms are easy to miss in the early stages but often include:

  • Difficulty completing routine tasks
  • Getting loss or losing things
  • Missing appointments
  • Forgetting recent events or conversations
  • Poor judgment, especially with finances
  • Difficulty finding words or writing
  • Personality changes
  • Withdrawing from work or social activities

What proteins are associated with Alzheimer’s disease?

Alzheimer’s is thought to be caused by the abnormal build-up of two proteins in the brain. One called amyloid is involved in the formation of plaques around brain cells. The other called tau causes the formation of twisted clusters of dead and dying nerve cells known as neurofibrillary tangles.

What neurotransmitters play a role in Alzheimer’s disease?

Two neurotransmitters involved in memory and learning—called acetylcholine (ACH) and glutamate—appear to play a role in Alzheimer’s disease. On the one hand, plaques appear to stimulate the production of chemicals that break down ACH, leading to their depletion. On the other, the progressive death of brain cells triggers the overproduction of glutamate, which overexcites brain cells and eventually kills them.

What causes death in people with Alzheimer’s disease?

The progressive destruction of nerve connections in the brain can eventually disrupt vital functions like swallowing. The majority of Alzheimer’s death are the result of aspiration pneumonia related to the onset of dysphagia (difficulty swallowing). When this occurs, food or liquid can enter the trachea (windpipe) and cause injury or infection in the lungs that leads to pneumonia.

A Word From Verywell

The good news about the risk factors for Alzheimer's disease is that you can take action to reduce many of them and improve your health overall. Eating a healthy diet, exercising, and managing your health conditions will help protect your brain and heart. You can help the older people in your life by visiting with them, taking them to social events they enjoy, and playing games that will exercise their cognitive powers. An active mind is a healthy mind.

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