What Is Alzheimer’s Disease? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Alzheimer’s disease is a progressive, irreversible brain disorder that slowly destroys memory and cognition — the ability to think and reason.

Alzheimer’s disease is the most common form of dementia among older adults. Most people with this disorder will begin to show symptoms in their mid-sixties, according to the National Institute on Aging. (1)

While there is currently no cure for Alzheimer’s, there is medication that can improve symptoms for a time.

Scientists are working to understand the biological pathways behind Alzheimer’s disease, with the goal of finding new and better treatments.

Researchers are also attempting to identify any measures that could help delay or prevent Alzheimer’s disease, including drugs therapies and nondrug interventions. (1)

Alzheimer’s and the Brain

Alzheimer’s disease is named for a German psychiatrist and neuropathologist named Alois Alzheimer. While conducting a postmortem in 1906, the doctor noticed abnormalities in the brain of a woman with a mysterious illness that caused memory loss, language problems, unpredictable behavior, and ultimately death.

The woman’s brain, Alzheimer reported, had many abnormal protein clumps (now called amyloid plaques) as well as tangled bundles of fibers (now called neurofibrillary, or tau, tangles). Those clumps and tangles are today considered the hallmarks of Alzheimer’s disease.

Alzheimer’s disease causes nerve cells (neurons) to stop functioning, lose their connections with other neurons, and die.

Typically, the damage first affects the parts of the brain that form memories. Eventually neurons in other areas of the brain also begin to die, causing the brain to shrink.

By the final stage of the disease, a person’s brain tissue will have shrunk significantly. (1)

The Role of Plaques and Tangles

Scientists aren’t completely sure about why neurons die and tissue shrinks in the brains of people with Alzheimer’s disease, but they strongly suspect that amyloid plaques and tau tangles are the cause.

The thinking is that plaques form when pieces of a protein called beta-amyloid clump together. Researchers are beginning to think that groups of a few pieces of beta-amyloid, rather than plaques, may cause the worst damage by blocking the chemical signals neurons use to communicate.

In healthy brain tissue, tau protects the transport systems that supply cells with nutrients and other important substances. But when tau forms tangles, cells can’t get the essentials they need and begin to die, according to the Alzheimer’s Association. (2)

However, there is new controversy surrounding the role of beta-amyloid in Alzheimer’s, so more research is needed on the subject.

While a certain amount of forgetfulness — losing things from time to time, sometimes forgetting which word to use — is a normal aspect of aging, certain types of memory loss can indicate either the possibility or the presence of early-stage Alzheimer’s disease.

Scientists have identified a condition called mild cognitive impairment (MCI) that for some (not all) people is a harbinger of Alzheimer’s dementia. MCI involves problems with memory or mental function that are noticeable to the person affected but not serious enough to interfere with everyday life.

Men and women who have MCI may be at higher risk of developing Alzheimer’s or other forms of dementia than individuals who don’t. But MCI doesn’t always progress; some people even get their cognitive abilities back. Researchers are trying to figure out why, notes the Mayo Clinic. (3)

Signs and Symptoms of Early-Stage Alzheimer’s Disease

Symptoms are generally mild to start, but become more noticeable as the disease progresses. The person may begin having difficulty with:

• Memory Losing items like keys around the house, forgetting a friend’s name or a recent conversation, getting lost in a familiar place.
• Speech Repeating oneself or struggling to follow a conversation.
• Visual Perception Difficulty seeing things in three dimensions and judging distances.
• Concentrating, Organizing, or Planning Struggling to make decisions, solve problems, or complete multistep tasks, like cooking a meal. 
• Orientation Getting confused about where they are or the time or date.
• Mood Feeling anxious, depressed, or irritable.

Signs and Symptoms of Later-Stage Alzheimer’s Disease

As the disease becomes more advanced, symptoms above become more pronounced. According to the Alzheimer’s Society, people may also experience: (4)

• Delusions For instance, believing, without reason, that someone is stealing from them
• Uncharacteristic Behavior Exhibiting aggression or agitation, calling out, or having disturbed sleep patterns
• Difficulty Walking and Talking Becoming bedridden or wheelchair-bound and requiring round-the-clock care to help with eating, drinking, and toileting

Learn More About Signs and Symptoms of Alzheimer’s Disease

What causes Alzheimer’s? That is the billion-dollar question of dementia research. Scientists have made progress in understanding what happens in the brain as the disease progresses, but they still don’t know just what kicks off these changes.

Researchers believe that the vast majority of Alzheimer’s cases are due to some combination of genetics, lifestyle, and environment. Risk factors include:

• Age Alzheimer’s disease is not a normal part of aging, with many people entering their nineties with their cognitive abilities intact. But age increases risk: Most people with the disease are 65 and older. After 65, risk doubles every five years. Nearly one-third of people who are 85 and older have Alzheimer’s.
• Family History Having a first-degree relative such as a parent or sibling with the disease is a strong risk factor. This may reflect shared genetics, environmental factors, or both.
• Genetics Scientists have identified over 20 genes involved with Alzheimer’s, although only one gene variant, called APOE-e4, appears to significantly raise risk. Still, some people with the APOE-e4 gene never develop Alzheimer’s, while others who develop Alzheimer’s don’t have the gene. (5,6)

Risk factors for Alzheimer’s that may be somewhat under a person’s control include:

• Head Injury Researchers have identified a link between traumatic brain injury and different types of dementia, including Alzheimer’s. Wearing a seat belt in a car or a helmet while playing certain kinds of sports, or minimizing fall risks in the home can offer protection.
• Cardiovascular Problems When the heart or blood vessels are damaged or diseased, the body is unable to pump enough blood to the brain, depriving cells of the oxygen they need to function. Conditions such as heart disease, stroke, high blood pressure, high cholesterol, and diabetes may raise risk.
  
• Poor Overall Health Researchers believe that poor overall health (linked to habits like smoking, for instance) may increase Alzheimer’s risk. (5)

Learn More About Causes of Alzheimer’s Disease: Common Risk Factors, Genetics, and More

Is Alzheimer’s Hereditary?

Although the genes you inherit from your parents can raise your risk of developing Alzheimer’s, researchers say that only rarely is Alzheimer’s caused by mutations (defects) that are passed directly from parent to child.

Those cases almost always involve early-onset Alzheimer’s disease, an uncommon type that develops before age 65.

Alzheimer’s disease caused by gene mutations accounts for between 7 and 12 percent of all cases of early-onset Alzheimer’s and less than 1 percent of all Alzheimer’s cases, according to the Alzheimer’s Society. (7)

There is no single Alzheimer’s test that can determine if a person has the disease. Instead, doctors may use a number of diagnostic methods: (8)

• Medical history
• Physical exam and diagnostic tests
• Neurological exam
• Mental status tests
• Brain imaging

Medical History

Healthcare practitioners ask about current and past illnesses and medication, and inquire about health issues affecting family members, such as Alzheimer’s and other forms of dementia.

Physical Exam and Diagnostic Tests

Doctors listen to the heart and lungs and examine other relevant areas. They may also collect blood and urine samples for lab testing and perform additional assessments to help identify ailments (like depression, untreated sleep apnea, delirium, certain vitamin deficiencies, side effects of medication, thyroid problems, and excess alcohol use) that may cause dementia-like symptoms.

Neurological Exam

A neurological exam that tests strength, sensation, reflexes, and eye movements can evaluate for medical conditions that may lead to impaired memory and cognition, like strokes or Parkinson’s disease.

Mental Status Tests

This testing assesses memory, ability to solve simple problems, and other cognitive skills. During a test called the Mini-Cog, for instance, the person is asked to remember and, a few minutes later, repeat the names of three common objects. The doctor will also ask questions to determine whether the person has a mood disorder that can cause symptoms that mimic Alzheimer’s dementia.

Brain Imaging

A brain scan, such as magnetic resonance imaging (MRI) or computerized tomography (CT) scans, could be used to rule out the presence of a tumor or another abnormality that might be responsible for Alzheimer’s-like symptoms.

Learn More About Diagnosing Alzheimer’s Disease: Tests and Screenings, Early Diagnosis, and Your Doctors

There are a number of different ways to describe the progression of Alzheimer’s disease. Although many experts use just three overall terms — “mild,” “moderate,” and “severe” — one commonly used guideline breaks these categories down further into seven stages, according to the Fisher Center for Alzheimer’s Research: (9)

• Stage 1: Normal
• Stage 2: Normal aged forgetfulness
• Stage 3: Mild cognitive impairment
• Stage 4: Mild Alzheimer’s disease
• Stage 5: Moderate Alzheimer’s disease
• Stage 6: Moderately severe Alzheimer’s disease
• Stage 7: Severe Alzheimer’s disease

Stage 1: Normal

People of any age can be free of any signs of cognitive or functional decline or associated changes in behavior or mood. These mentally healthy people belong in this “normal” stage 1 category.

Stage 2: Normal Aged Forgetfulness

One-half or more of older adults ages 65 and older believe their memory is slipping a bit — that they have more trouble remembering names than they used to, for instance.

Stage 3: Mild Cognitive Impairment

Memory problems are subtle but significant enough for close friends and family to notice. The person might ask the same question repeatedly or have trouble acquiring new skills or performing multi-part tasks.

Stage 4: Mild Alzheimer’s Disease

People at this stage may become increasingly unable to handle the more complex demands of daily life, such as ordering off a menu at a restaurant.

Stage 5: Moderate Alzheimer’s Disease

The basic demands of everyday life, like picking out clothing suitable for the weather, become difficult. People may not be able to remember the name of the president or count backwards from 20 by twos.

Stage 6: Moderately Severe Alzheimer’s Disease

People may have trouble walking or putting on their clothing correctly, and become reliant on caregivers for help with bathing and using the toilet. The end of this stage is marked by incontinence and inability to speak.

Stage 7: Severe Alzheimer’s Disease

Speech is essentially lost. People lose the ability to walk and sit up independently, to smile, and to hold their heads up without assistance. Physical rigidity sets in.

Prognosis of Alzheimer’s Disease

Alzheimer’s disease is irreversible and ultimately fatal.

Learn More About the Stages of Progression of Alzheimer’s

The brain changes that result in Alzheimer’s disease may begin a decade or more before the first symptoms appear, as amyloid plaques and tau tangles start to form, neurons die, and other toxic changes in the brain begin to occur. (1)

After diagnosis, a person with Alzheimer’s will live, on average, from 4 to 8 years, though some survive for as long as 20 years. (10)

While there is currently no cure for Alzheimer’s disease, treatments can slow cognitive decline for a limited time, manage behavioral symptoms, and provide relief for symptoms like anxiety and depression.

Nondrug Approaches

Before healthcare providers prescribe medication, they generally start with nonpharmaceutical approaches. Counseling, involvement in a support group, and activities like dancing that combine social, mental, and physical engagement can all have a positive effect on mind and body, notes the Alzheimer’s Society. (11)

Medication Options

The U.S. Food and Drug Administration (FDA) has approved a small number of Alzheimer’s drugs, which are believed to work by altering levels of neurotransmitters (chemical messengers) in the brain. Those include donepezil (Aricept), rivastigmine (Exelon), galantamine (Razadyne), and memantine (Namenda).

In 2021, the FDA approved aducanumab (Aduhelm), a monoclonal antibody drug that targets the beta-amyloid clusters that turn into plaque, and which is also the first infusion treatment the FDA has approved for Alzheimer’s. Aducanumab has shown to reduce beta-amyloid plaques in the brain. However, more recent investigations have cast doubt on the role of beta-amyloid in Alzheimer’s. In addition, aducanumab does not reverse the progression of Alzheimer’s for those who have already developed symptoms, and some patients have developed serious side effects, such as brain swelling and bleeding.

Doctors may also prescribe drugs for people experiencing behavioral symptoms of Alzheimer’s, such as depression, aggression, restlessness, and anxiety.

Research efforts on new Alzheimer’s treatments have been frustrating, with promising possibilities failing in clinical trials. But scientists are continuing to explore new interventions, according to the National Institute on Aging. (12)

Alternative and Complementary Therapies

Despite the growing number of herbal remedies, dietary supplements, and “medical foods” aimed at people with Alzheimer’s, there is no scientific proof that any of these products work.

For instance, some people with Alzheimer’s consume coconut oil based on the theory that the caprylic acid in the oil can provide energy to brain cells that are no longer able to metabolize glucose. But there has been no research confirming that this helps cognition. (13)

Learn More About Treatment for Alzheimer’s: Medication, Alternative and Complementary Therapies, and More

In advanced stages of Alzheimer’s disease, complications from severe loss of brain function can include dehydration, malnutrition, or infection.

One common complication is difficulty swallowing (dysphagia), which can result in food or drink being aspirated (breathed) into the lungs, potentially causing pneumonia. Pneumonia is a common cause of death for people with severe Alzheimer’s, notes the Mayo Clinic. (14)

Can a healthy lifestyle reduce Alzheimer’s risk? A growing body of research suggests it can.

For instance, a 2019 study found that people who were genetically predisposed to develop Alzheimer’s reduced their risk by 32 percent by pursuing a healthy lifestyle that involved:

• Not smoking
• Exercising regularly
• Eating a healthy diet
• Consuming alcohol only moderately (15)

Learn More About Preventing Alzheimer’s Disease: Exercise, Diet, and More

More than six million people in the United States are living with Alzheimer’s, and 1 in 3 seniors dies with Alzheimer’s or another dementia, according to the Alzheimer’s Association

As the number of older Americans rises, reflecting advances in medicine and the aging of the baby boomers, the number of people with Alzheimer’s is expected to more than double to as many as 13 million by 2050, barring any significant medical breakthroughs. (16)

Although the terms “dementia” and “Alzheimer’s disease” are sometimes used interchangeably, they are not the same thing.

Dementia isn’t a specific disease, but rather a general term to describe any decline in brain function that affects memory, language, and other cognitive abilities, and that is serious enough to interfere with daily life.

Alzheimer’s disease is the most common type of dementia, accounting for 60 to 80 percent of all dementia cases. (17)

It is very common for people with Alzheimer’s disease to simultaneously experience brain abnormalities related to other types of dementia, a condition called mixed dementia.

Other types of dementia include:

• Vascular Dementia The most prevalent type of mixed dementia involves Alzheimer’s combined with vascular dementia, in which brain cells are deprived of essential nutrients and oxygen because of conditions that block or reduce blood flow to the brain.
• Lewy Body Dementia People with Alzheimer’s may also simultaneously experience Lewy body dementia, a disease marked by abnormal clumps of the protein alpha-synuclein in brain cells.

Some people may simultaneously experience brain changes related to all three conditions — Alzheimer’s, vascular dementia, and Lewy body dementia. (18)

Living With Alzheimer’s

Preserving quality of life for as long as possible is an achievable goal for a person with Alzheimer’s. The key is having strategies in place to maximize independence, minimize frustration, and build feelings of confidence and emotional connection that help make every day the best it can be.

Routines can ease the burden of short-term memory loss for people in the earlier stages of dementia. If you have Alzheimer’s, you might feel calmer and more in control knowing that your house keys are always on a hook by the door, for instance, or that your caregiver always records appointments on a wall calendar.

As the disease progresses, patients have more difficulty verbalizing their wants and needs to others. If you are a caregiver, there are strategies that can help you and the person you care for meet this challenge.

Keeping the mood positive, reducing distractions like TV, and making your questions easy to answer with a “yes” or “no” can all make a huge difference. Sometimes body language and nonverbal cues can express what words no longer are able to, notes the Family Caregiver Alliance. (19)

Learn More About Living With Alzheimer’s: Routines, Accident-Proofing, Communication Tips, and More

Early-Onset Alzheimer’s

Early-onset Alzheimer’s describes Alzheimer’s dementia that affects people younger than 65.

An estimated 7 to 12 percent of these patients have inherited specific gene mutations (defects) from a parent. Scientists have identified around 500 families around the world with this particular type of familial Alzheimer’s.

For everyone else with early-onset Alzheimer’s, the same risk factors as those for late-onset Alzheimer’s come into play: genetics, lifestyle, and environmental influences interacting in complicated and still not clearly understood ways. (7)

Learn More About Early-Onset Alzheimer’s Disease: Causes, Symptoms, Diagnosis, and Treatment

Patients with Alzheimer’s and their families have access to resources that can provide urgently needed help.

The U.S. federal government offers assistance via online portals like Alzheimers.gov that provide information on how to connect with healthcare professionals, support services, research studies looking for participants, and other opportunities.

The Alzheimer’s Association, a leading nonprofit, is an invaluable resource. The organization operates a 24/7 toll-free helpline (800-272-3900) as well as message boards to help those affected by the disease find community.

There are also organizations that focus on one particular challenge. NeedyMeds, for instance, provides support for patients who can’t afford prescription medication.

Learn More About Additional Resources and Support for People With Alzheimer’s