What Is Alzheimer’s Disease?
Alzheimer’s disease is a brain disorder that slowly destroys memory and thinking skills and, eventually, the ability to carry out the simplest tasks. In most people with the disease — those with the late-onset type symptoms first appear in their mid-60s. Early-onset Alzheimer’s occurs between a person’s 30s and mid-60s and is very rare. Alzheimer’s disease is the most common cause of dementia among older adults.
The disease is named after Dr. Alois Alzheimer. In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. Her symptoms included memory loss, language problems, and unpredictable behavior. After she died, he examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary, or tau, tangles).
These plaques and tangles in the brain are still considered some of the main features of disease. Another feature is the loss of connections between nerve cells (neurons) in the brain. Neurons transmit messages between different parts of the brain, and from the brain to muscles and organs in the body. Many other complex brain changes are thought to play a role in too.
This damage initially takes place in parts of the brain involved in memory, including the entorhinal cortex and hippocampus. It later affects areas in the cerebral cortex, such as those responsible for language, reasoning, and social behavior. Eventually, many other areas of the brain are damaged.
How many Americans have Alzheimer’s disease?
Estimates vary, but experts suggest that more than 6 million Americans age 65 and older may have Alzheimer’s. Many more under age 65 also have the disease. Unless Alzheimer’s can be effectively treated or prevented, the number of people with it will increase significantly if current population trends continue. This is because increasing age is the most important known risk factor for disease.
What does Alzheimer’s disease look like?
Memory problems are typically one of the first signs of , though initial symptoms may vary from person to person. A decline in other aspects of thinking, such as finding the right words, vision/spatial issues, and impaired reasoning or judgment, may also signal the very early stages of disease. Mild cognitive impairment (MCI) is a condition that can be an early sign of Alzheimer’s, but not everyone with MCI will develop the disease.
People with Alzheimer’s have trouble doing everyday things like driving a car, cooking a meal, or paying bills. They may ask the same questions over and over, get lost easily, lose things or put them in odd places, and find even simple things confusing. As the disease progresses, some people become worried, angry, or violent.
How long can a person live with Alzheimer’s disease?
The time from diagnosis to death varies — as little as three or four years if the person is older than 80 when diagnosed, to as long as 10 or more years if the person is younger.
disease is currently ranked as the sixth leading cause of death in the United States, but recent estimates indicate that the disorder may rank third, just behind heart disease and cancer, as a cause of death for older people.
Currently, there is no cure for disease, though there has been significant progress in recent years in developing and testing new treatments. Several medicines have been approved by the U.S. Food and Drug Administration to treat people with Alzheimer’s.
Learn more about how disease is treated.
Read about this topic in Spanish. Lea sobre este tema en español.
The basics of Alzheimer’s disease
Scientists are conducting studies to learn more about plaques, tangles, and other biological features of disease. Advances in brain imaging techniques allow researchers to see the development and spread of abnormal amyloid and tau proteins in the living brain, as well as changes in brain structure and function. Scientists are also exploring the very earliest steps in the disease process by studying changes in the brain and body fluids that can be detected years before symptoms appear. Findings from these studies will help in understanding the causes of Alzheimer’s and make diagnosis easier.
One of the great mysteries of Alzheimer’s disease is why it largely affects older adults. Research on normal brain aging is exploring this question. For example, scientists are learning how age-related changes in the brain may harm neurons and affect other types of brain cells to contribute to damage. These age-related changes include atrophy (shrinking) of certain parts of the brain, inflammation, blood vessel damage, production of unstable molecules called free radicals, and mitochondrial dysfunction (a breakdown of energy production within a cell).
Symptoms
Memory loss is the key symptom of disease. Early signs include difficulty remembering recent events or conversations. As the disease progresses, memory impairments worsen and other symptoms develop.
At first, a person with disease may be aware of having difficulty remembering things and organizing thoughts. A family member or friend may be more likely to notice how the symptoms worsen.
Brain changes associated with disease lead to growing trouble with:
Memory
Everyone has occasional memory lapses, but the memory loss associated with disease persists and worsens, affecting the ability to function at work or at home.
People with Alzheimer’s may:
- Repeat statements and questions over and over
- Forget conversations, appointments or events, and not remember them later
- Routinely misplace possessions, often putting them in illogical locations
- Get lost in familiar places
- Eventually forget the names of family members and everyday objects
- Have trouble finding the right words to identify objects, express thoughts or take part in conversations
Thinking and reasoning
Alzheimer’s disease causes difficulty concentrating and thinking, especially about abstract concepts such as numbers.
Multitasking is especially difficult, and it may be challenging to manage finances, balance checkbooks and pay bills on time. Eventually, a person with may be unable to recognize and deal with numbers.
Making judgments and decisions
Alzheimer’s causes a decline in the ability to make reasonable decisions and judgments in everyday situations. For example, a person may make poor or uncharacteristic choices in social interactions or wear clothes that are inappropriate for the weather. It may be more difficult to respond effectively to everyday problems, such as food burning on the stove or unexpected driving situations.
Planning and performing familiar tasks
Once-routine activities that require sequential steps, such as planning and cooking a meal or playing a favorite game, become a struggle as the disease progresses. Eventually, people with advanced often forget how to perform basic tasks such as dressing and bathing.
Changes in personality and behavior
Brain changes that occur in disease can affect moods and behaviors. Problems may include the following:
- Depression
- Apathy
- Social withdrawal
- Mood swings
- Distrust in others
- Irritability and aggressiveness
- Changes in sleeping habits
- Wandering
- Loss of inhibitions
- Delusions, such as believing something has been stolen
Preserved skills
Many important skills are preserved for longer periods even while symptoms worsen. Preserved skills may include reading or listening to books, telling stories and reminiscing, singing, listening to music, dancing, drawing, or doing crafts.
These skills may be preserved longer because they are controlled by parts of the brain affected later in the course of the disease.
When to see a doctor
A number of conditions, including treatable conditions, can result in memory loss or other dementia symptoms. If you are concerned about your memory or other thinking skills, talk to your doctor for a thorough assessment and diagnosis.
If you are concerned about thinking skills you observe in a family member or friend, talk about your concerns and ask about going together to a doctor’s appointment.
Causes
The exact causes of Alzheimer’s disease aren’t fully understood. But at a basic level, brain proteins fail to function normally, which disrupts the work of brain cells (neurons) and triggers a series of toxic events. Neurons are damaged, lose connections to each other and eventually die.
Scientists believe that for most people, disease is caused by a combination of genetic, lifestyle and environmental factors that affect the brain over time.
Less than 1% of the time, Alzheimer’s is caused by specific genetic changes that virtually guarantee a person will develop the disease. These rare occurrences usually result in disease onset in middle age.
The damage most often starts in the region of the brain that controls memory, but the process begins years before the first symptoms. The loss of neurons spreads in a somewhat predictable pattern to other regions of the brains. By the late stage of the disease, the brain has shrunk significantly.
Researchers trying to understand the cause of Alzheimer’s disease are focused on the role of two proteins:
Plaques. Beta-amyloid is a fragment of a larger protein. When these fragments cluster together, they appear to have a toxic effect on neurons and to disrupt cell-to-cell communication. These clusters form larger deposits called amyloid plaques, which also include other cellular debris.
Tangles. Tau proteins play a part in a neuron’s internal support and transport system to carry nutrients and other essential materials. In disease, tau proteins change shape and organize themselves into structures called neurofibrillary tangles. The tangles disrupt the transport system and are toxic to cells.
Risk factors
Age
Increasing age is the greatest known risk factor for disease. Alzheimer’s is not a part of normal aging, but as you grow older the likelihood of developing Alzheimer’s disease increases.
One study, for example, found that annually there were four new diagnoses per 1,000 people ages 65 to 74, 32 new diagnoses per 1,000 people ages 75 to 84, and 76 new diagnoses per 1,000 people age 85 and older.
Family history and genetics
Your risk of developing Alzheimer’s is somewhat higher if a first-degree relative — your parent or sibling — has the disease. Most genetic mechanisms of among families remain largely unexplained, and the genetic factors are likely complex.
One better understood genetic factor is a form of the apolipoprotein E gene (APOE). A variation of the gene, APOE e4, increases the risk of Alzheimer’s disease. Approximately 25% to 30% of the population carries an APOE e4 allele, but not everyone with this variation of the gene develops the disease.
Scientists have identified rare changes (mutations) in three genes that virtually guarantee a person who inherits one of them will develop Alzheimer’s. But these mutations account for less than 1% of people with disease.
Down syndrome
Many people with Down syndrome develop disease. This is likely related to having three copies of chromosome 21 — and subsequently three copies of the gene for the protein that leads to the creation of beta-amyloid. Signs and symptoms of Alzheimer’s tend to appear 10 to 20 years earlier in people with Down syndrome than they do for the general population.
Sex
There appears to be little difference in risk between men and women, but, overall, there are more women with the disease because they generally live longer than men.
Mild cognitive impairment
Mild cognitive impairment (MCI) is a decline in memory or other thinking skills that is greater than normal for a person’s age, but the decline doesn’t prevent a person from functioning in social or work environments.
People who have MCI have a significant risk of developing dementia. When the primary MCI deficit is memory, the condition is more likely to progress to dementia due to disease. A diagnosis of MCI encourages a greater focus on healthy lifestyle changes, developing strategies to make up for memory loss and scheduling regular doctor appointments to monitor symptoms.
Head trauma
People who’ve had a severe head trauma have a greater risk of disease. Several large studies found that in people age 50 years or older who had a traumatic brain injury (TBI), the risk of dementia and disease increased. The risk increases in people with more-severe and multiple TBIs. Some studies indicate that the risk may be greatest within the first six months to two years after the TBI.
Air pollution
Studies in animals have indicated that air pollution particulates can speed degeneration of the nervous system. And human studies have found that air pollution exposure — particularly from traffic exhaust and burning wood — is associated with greater dementia risk.
Excessive alcohol consumption
Drinking large amounts of alcohol has long been known to cause brain changes. Several large studies and reviews found that alcohol use disorders were linked to an increased risk of dementia, particularly early-onset dementia.
Poor sleep patterns
Research has shown that poor sleep patterns, such as difficulty falling asleep or staying asleep, are associated with an increased risk of disease.
Lifestyle and heart health
Research has shown that the same risk factors associated with heart disease may also increase the risk of Alzheimer’s disease. These include:
- Lack of exercise
- Obesity
- Smoking or exposure to secondhand smoke
- High blood pressure
- High cholesterol
- Poorly controlled type 2 diabetes
These factors can all be modified. Therefore, changing lifestyle habits can to some degree alter your risk. For example, regular exercise and a healthy low-fat diet rich in fruits and vegetables are associated with a decreased risk of developing Alzheimer’s disease.
Complications
Memory and language loss, impaired judgment and other cognitive changes caused by Alzheimer’s can complicate treatment for other health conditions. A person with Alzheimer’s disease may not be able to:
- Communicate that he or she is experiencing pain
- Explain symptoms of another illness
- Follow a prescribed treatment plan
- Explain medication side effects
As disease progresses to its last stages, brain changes begin to affect physical functions, such as swallowing, balance, and bowel and bladder control. These effects can increase vulnerability to additional health problems such as:
- Inhaling food or liquid into the lungs (aspiration)
- Flu, pneumonia and other infections
- Falls
- Fractures
- Bedsores
- Malnutrition or dehydration
- Constipation or diarrhea
- Dental problems such as mouth sores or tooth decay
Prevention
Alzheimer’s disease is not a preventable condition. However, a number of lifestyle risk factors for Alzheimer’s can be modified. Evidence suggests that changes in diet, exercise and habits — steps to reduce the risk of cardiovascular disease — may also lower your risk of developing disease and other disorders that cause dementia. Heart-healthy lifestyle choices that may reduce the risk of include the following:
- Exercising regularly
- Eating a diet of fresh produce, healthy oils and foods low in saturated fat such as a Mediterranean diet
- Following treatment guidelines to manage high blood pressure, diabetes and high cholesterol
- Asking your doctor for help to quit smoking if you smoke
Studies have shown that preserved thinking skills later in life and a reduced risk of Alzheimer’s disease are associated with participating in social events, reading, dancing, playing board games, creating art, playing an instrument, and other activities that require mental and social engagement.
Alzheimer’s and the brain
Microscopic changes in the brain begin long before the first signs of memory loss.
The brain has 100 billion nerve cells (neurons). Each nerve cell connects with many others to form communication networks. Groups of nerve cells have special jobs. Some are involved in thinking, learning and remembering. Others help us see, hear and smell.
To do their work, brain cells operate like tiny factories. They receive supplies, generate energy, construct equipment and get rid of waste. Cells also process and store information and communicate with other cells. Keeping everything running requires coordination as well as large amounts of fuel and oxygen.
Scientists believe disease prevents parts of a cell’s factory from running well. They are not sure where the trouble starts. But just like a real factory, backups and breakdowns in one system cause problems in other areas. As damage spreads, cells lose their ability to do their jobs and, eventually die, causing irreversible changes in the brain.
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