What Causes and Contributes to Alzheimer’s Disease & Commonly Heard Myths

Last Updated: August 13, 2020


There are so many known causes for Alzheimer’s disease (AD), and probably unknown causes as well, that it can be difficult to know how a specific person got it. However, researchers have come up with a list of risk factors that may make a person more likely to develop Alzheimer’s disease. They have also identified factors that decrease the risk. On this page, we’ll discuss fact and fiction related to what causes Alzheimer’s. We’ll also address popular myths and explain why they’re usually wrong.

 Confused by Terminology: Do you need a better understanding of what “risk factors” are? How they differ from “causes” and what it means when “dementia has been linked to” something? Read our primer on what these terms mean.  


Myths About the Cause of Alzheimer’s Disease

In recent years there have been several myths about what causes AD, including viruses, aluminum, and flu shots. Let’s take these one at a time to see if you really have anything to worry about:

Do viruses cause Alzheimer’s disease? What we know for sure is that the herpes virus can remain in the body long after a person gets it, and is found in the brains of some people with Alzheimer’s. When a brain fights a viral infection there is inflammation, and the brain creates amyloid beta proteins that decrease swelling but also form clumps that damage brain cells and cause Alzheimer’s. For this reason, people who have herpes virus, especially oral herpes with cold sores, are apparently at slightly higher risk of Alzheimer’s.

Another common illness that studies show increases risk of Alzheimer’s is gum disease. A person who gets bacterial infections in their gums is more likely to develop dementia than someone who does not. This is another reason oral hygiene is important.

In the 1960s, researchers found that high doses of aluminum in rabbits caused tau tangles that are found in the brains of people with Alzheimer’s disease. This has led some people to believe aluminum in cookware or soda cans may be causing Alzheimer’s disease through contact with our food and drinks. Several studies have looked at whether aluminum may cause dementia, however, and none have found a link. The amounts of aluminum that created tau tangles in those animal studies are much higher than what can possibly be ingested via contact with our food.

Flu Shots
Not only are flu shots not a cause of Alzheimer’s disease, they actually make someone less likely to get dementia, according to studies. Pneumonia vaccines have also been shown to reduce a person’s chances of developing dementia, researchers say. Though the reasons aren’t fully understood, it may be because the flu and pneumonia cause inflammation that leads to protein tangles in the brain, so less time spent sick because of the shots means less inflammation means less chance of weakened brain cells.

Silver Dental Fillings
A person with dental fillings is not more likely to get Alzheimer’s disease or related dementia, so it’s not causal, but studies have found that when someone does develop the illness in the brain, people with fillings have seen a faster progression of symptoms. The reason why remains unknown. The Food and Drug Administration, the Mayo Clinic, and the Alzheimer’s Association have all said that silver or “amalgam” (which mixes silver with other metals) fillings are safe.

Studies that identified a possible link between the trace amounts of aluminum in under-arm deodorant and an increased risk of Alzheimer’s disease were later shown as having been based on bad data. Other studies showed that almost no aluminum gets absorbed through the skin, and a link to dementia has not been shown.


Known Risk Factors for Alzheimer’s Disease

While there is no exact known cause(s) of Alzheimer’s disease, multiple factors may be involved. The following are risk factors for developing AD, which means there is a greater risk of the disease if any of these are present:

Old Age
Aging alone does not result in Alzheimer’s disease, but as one gets older the chances of developing the disease increase. After age 65, a person’s risk for developing AD doubles every 5 years, and after the age of 85, approximately one in three people are afflicted with the disease. Alzheimer’s disease is not a normal part of aging.

Family History
Having an immediate family member (mom, dad, brother, or sister) with AD increases the chance of developing the disease by about 30 percent. The more people in the family that have the disease, the greater the likelihood that other members will develop it.

In particular, it is suspected that early-onset familial Alzheimer’s disease (eFAD), which develops between ages 30-60, is caused by genetic mutations. Less than 10 percent of people with Alzheimer’s have the early-onset type. Late-onset AD, which develops after age 65, is the most common type.

Down Syndrome
Down Syndrome is a genetic disease that causes mental impairments and characteristic body and facial features. Unfortunately, almost everyone with Down Syndrome develops the plaques and tangles in their brains that cause Alzheimer’s disease, so AD is far more common in this population than in the general population. Fifty percent or more of individuals with Down Syndrome will develop Alzheimer’s, with symptoms more likely to start occurring in a person’s 50s. Studies suggest that individuals with a family history of Down Syndrome have a higher risk of developing AD.

Head Trauma
The Centers for Disease Control and Prevention estimates approximately 1.7 million Americans suffer head injuries (traumatic brain injury) every year. Injury that results in the loss of consciousness or amnesia is considered a traumatic brain injury. When researchers studied war veterans who had experienced TBI, they found that both moderate and severe head injuries in young men increased their odds of getting dementia, especially AD.

Researchers are still trying to determine why and how head injury contributes to the development of Alzheimer’s disease. Protective headgear and seat belts should be worn as often as possible to reduce head injury. (The disease Chronic Traumatic Encephalopathy has symptoms similar to Alzheimer’s disease and occurs in the brains of people like veterans and football players who suffer repeated blows to the head.)


Possible Risk Factors for Alzheimer’s Disease

Additional factors might contribute to the development of Alzheimer’s disease, but scientists are not sure about their direct link to the disease. More research will be needed to better understand the relationship between these factors and Alzheimer’s disease. In addition to the factors below, several others, such as smoking, stress, and depression, may put people at greater risk for developing Alzheimer’s disease.

Pollution in the air (in the form of particulate matter or ozone gas) has been shown in studies to be at least moderately tied to an increased likelihood of getting Alzheimer’s disease. Exposure to these chemicals and/or natural substances can cause many health problems, particularly in the lungs but also in other organs including the brain.

Evidence has shown that someone with the Alzheimer’s gene who lives in a city with more pollution experiences dementia symptoms an average of a decade earlier than a person with the same gene in a less-polluted environment. Researchers have been quick to point out, however, that more studies are needed to draw the link between environment and AD.

Women are at considerably more risk for developing Alzheimer’s than men; about two-thirds of people diagnosed with AD are women. The reason for this is not well understood, but it may be because women generally have a longer life expectancy than men, and the rate of AD increases with age. In addition, early menopause makes a person slightly more likely to get dementia, and lower levels of estrogen after menopause increase women’s chances of developing AD.

Cerebrovascular Disease / Cardiovascular Disease
Cardiovascular disease affects blood vessels and the heart. Hypertension, unhealthy cholesterol levels, and diabetes are cardiovascular diseases that studies say put a person at higher risk of getting Alzheimer’s disease, though the connection is not understood well enough to use these illnesses as a predictor for developing dementia.

Ailments that cause the blood flow to the brain to be altered are considered cerebrovascular disease. The most common cerebrovascular disease is stroke, and almost 800,000 Americans have a stroke annually. When a stroke deprives the brain of blood, which contains oxygen and food, brain cells can be damaged or die. This can lead directly to a form of dementia called Vascular dementia (VD), which is the second-most-common type of dementia, and there is evidence that Alzheimer’s disease also becomes more likely after a stroke.

Parkinson’s Disease
Parkinson’s disease (PD) is a progressive and irreversible neurological disease that produces tremors, impaired balance, rigid movements, and extremely slow movements during routine tasks, such as getting dressed. Between 50 and 80 percent of individuals with Parkinson’s will develop Parkinson’s disease dementia. The symptoms associated with PD and AD are often very similar and it can be difficult to distinguish one from the other. AD generally develops in late stages of PD. Similarly, individuals in the late stages of AD often have symptoms of PD.

Diets high in fat, red meat, sugar, and sodium can put people at greater risk of developing Alzheimer’s. These unhealthy foods are linked to heart disease and strokes, and brain damage occurs when these diseases starve the brain of blood, with symptoms similar to Alzheimer’s.
A good diet (including fruits and vegetables, whole grains, fish, poultry, and nuts) can reduce the likelihood of developing dementia. Eating good food lowers inflammation, which is linked to dementia, and protects brain cells from chemicals called free radicals that can do damage and might lead to Alzheimer’s. Also, obesity (specifically excess belly fat) in middle-aged people has been linked to an increased risk of AD in studies.


Reducing the Risk of Alzheimer’s Disease

Several factors that may reduce the risk or actually prevent Alzheimer’s disease and other forms of dementia are currently being explored. For example: exercise, a healthy diet, having an active social life, and limiting alcohol appear to be important.