Causes and Risk Factors of Alzheimer's Disease

In This Article

Scientists are still trying to fully understand the cause or causes of Alzheimer’s disease. In the meantime, it’s helpful to understand the hallmarks of Alzheimer’s—plaques and tangles—and the risk factors that affect a person’s likelihood of developing the disease.

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. One theory is that they block nerve cells’ ability to communicate with each other, making 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. However, several risk factors for Alzheimer’s disease have been uncovered.

Age Risk Factor

Advancing age is the number one risk factor for developing Alzheimer’s disease. One out of eight people over the age of 65 has Alzheimer’s disease, and almost one out of every two people over the age of 85 have Alzheimer’s. The probability of being diagnosed with Alzheimer’s nearly doubles every five years after age 65.

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, which increases the risk of Alzheimer's disease.

Genetics

People who have a parent or sibling that developed Alzheimer’s disease are two to three times more likely to develop the disease than those with no family history of Alzheimer’s. 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 familial risk factor. The first is thought to be a “risk gene,” ApoE 4, 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” and is much rarer than risk genes. 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 is 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, or 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 stroke and cerebral infarcts, which in turn raise your risk for dementia.

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

A 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, scientists have also identified several lifestyle factors that can influence a person’s risk 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. Using safety equipment such as helmets when riding a bicycle, skiing, skateboarding, or playing sports is essential. As older people are more at risk of falls, check the home for tripping hazards and install safety equipment such as handrails where needed.

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 can raise your risks.

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

If you have heard that aluminum might be a risk factor for Alzheimer's disease, this is outdated speculation. The Alzheimer's Association reports that no studies have confirmed any role for aluminum in causing Alzheimer's disease.

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.

Was this page helpful?

Article Sources