Alzheimer's is a type of dementia that affects memory, thinking and behavior. Symptoms eventually grow severe enough to interfere with daily tasks.
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Understanding Alzheimer's and dementia
Alzheimer's is the most common cause of dementia, a general term for memory loss and other cognitive abilities serious enough to interfere with daily life. Alzheimer's disease accounts for 60-80% of dementia cases.
Learn more: What is the Difference Between Dementia and Alzheimer's?, What is Dementia, Research and Progress
Alzheimer's is not a normal part of aging. The greatest known risk factor is increasing age, and the majority of people with Alzheimer's are 65 and older. Alzheimer’s disease is considered to be younger-onset Alzheimer’s if it affects a person under 65. Younger-onset can also be referred to as early-onset Alzheimer’s. People with younger-onset Alzheimer’s can be in the early, middle or late stage of the disease.
Learn more: Younger/Early-Onset Alzheimer's, Risk Factors
Alzheimer's worsens over time. Alzheimer's is a progressive disease, where dementia symptoms gradually worsen over a number of years. In its early stages, memory loss is mild, but with late-stage Alzheimer's, individuals lose the ability to carry on a conversation and respond to their environment. On average, a person with Alzheimer's lives 4 to 8 years after diagnosis but can live as long as 20 years, depending on other factors.
Learn more: 10 Warning Signs, Stages of Alzheimer's Disease
Alzheimer's as a Continuum
Alzheimer's disease progresses in stages, with the severity of symptoms increasing over time.
Select a stage to learn more.
An asymptomatic individual may have biological changes of Alzheimer's in their brain but no cognitive symptoms. Hallmarks of Alzheimer's, such as amyloid buildup, may be present up to 20 years before someone exhibits changes in memory, thinking or behavior.
MCI is an early stage of memory loss or other loss of cognitive ability in an individual who maintains the ability to independently perform most activities of daily living. Some people living with MCI may develop dementia, but others will not. MCI can be an early stage of Alzheimer's if hallmark brain changes are present. Learn more about MCI
If those changes are present, the person may progress into dementia due to Alzheimer's disease, which can be divided into three stages — mild, moderate and severe — representing a progressive loss of independence. Learn more about the stages
A person living with mild dementia due to Alzheimer's disease will typically start to experience symptoms that interfere with some daily activities.
Symptoms are more pronounced for someone living with moderate dementia due to Alzheimer's disease and will interfere with many of their daily activities.
An individual living with severe dementia due to Alzheimer's disease will experience symptoms that interfere with most everyday activities.
Alzheimer's has no cure, but two treatments — aducanumab (Aduhelm®) and lecanemab (Leqembi®) — demonstrate that removing beta-amyloid, one of the hallmarks of Alzheimer’s disease, from the brain reduces cognitive and functional decline in people living with early Alzheimer’s. (Aducanumab will be discontinued on Nov. 1, 2024. Please connect with your provider on treatment options.) Other treatments can temporarily slow the worsening of dementia symptoms and improve quality of life for those with Alzheimer's and their caregivers. Today, there is a worldwide effort underway to find better ways to treat the disease, delay its onset and prevent it from developing.
Learn more: Treatments, Treatment Horizon, Prevention, Clinical Trials
Symptoms of Alzheimer's
The most common early symptom of Alzheimer's is difficulty remembering newly learned information.
Just like the rest of our bodies, our brains change as we age. Most of us eventually notice some slowed thinking and occasional problems with remembering certain things. However, serious memory loss, confusion and other major changes in the way our minds work may be a sign that brain cells are failing.
Alzheimer's changes typically begin in the part of the brain that affects learning. As Alzheimer's advances through the brain it leads to increasingly severe symptoms, including disorientation, mood and behavior changes; deepening confusion about events, time and place; unfounded suspicions about family, friends and professional caregivers; more serious memory loss and behavior changes; and difficulty speaking, swallowing and walking.
People with memory loss or other possible signs of Alzheimer’s may find it hard to recognize they have a problem. Signs of dementia may be more obvious to family members or friends. Anyone experiencing dementia-like symptoms should see a doctor as soon as possible. If you need assistance finding a doctor with experience evaluating memory problems, your local Alzheimer's Association can help. Earlier diagnosis and intervention methods are improving dramatically, and treatment options and sources of support can improve quality of life. Two helpful support resources you can tap into are ALZConnected, our message boards and online social networking community, and Alzheimer's Navigator, a web tool that creates customized action plans, based on answers you provide through short, online surveys.
Take our free, online education courses: Understanding Alzheimer's and Dementia and Know the 10 Signs: Early Detection Matters
Help is available
If you or someone you know has been diagnosed with Alzheimer's or another dementia, you are not alone. The Alzheimer's Association is the trusted resource for reliable information, education, referral and support to millions of people affected by the disease.
Alzheimer's is not the only cause of memory loss
Many people have trouble with memory — this does NOT mean they have Alzheimer's. There are many different causes of memory loss. If you or someone you know is experiencing symptoms of dementia, it is best to visit a doctor so the cause can be determined.
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 Alzheimer's 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.
The role of plaques and tangles
Two abnormal structures called plaques and tangles are prime suspects in damaging and killing nerve cells.
- Plaques are deposits of a protein fragment called beta-amyloid (BAY-tuh AM-uh-loyd) that build up in the spaces between nerve cells.
- Tangles are twisted fibers of another protein called tau (rhymes with “wow”) that build up inside cells.
Though autopsy studies show that most people develop some plaques and tangles as they age, those with Alzheimer’s tend to develop far more and in a predictable pattern, beginning in the areas important for memory before spreading to other regions.
Scientists do not know exactly what role plaques and tangles play in Alzheimer's disease. Most experts believe they somehow play a critical role in blocking communication among nerve cells and disrupting processes that cells need to survive.
It's the destruction and death of nerve cells that causes memory failure, personality changes, problems carrying out daily activities and other symptoms of Alzheimer's disease.
Learn More: Take the Brain Tour
Research and progress
In 1906, German physician Dr. Alois Alzheimer first described "a peculiar disease" — one of profound memory loss and microscopic brain changes — a disease we now know as Alzheimer's.
Today, Alzheimer's is at the forefront of biomedical research. Researchers are working to uncover as many aspects of Alzheimer's disease and other dementias as possible. Some of the most remarkable progress has shed light on how Alzheimer's affects the brain. The hope is this better understanding will lead to new treatments. Many potential approaches are currently under investigation worldwide. Sign up for our weekly E-News to receive updates about Alzheimer’s and dementia care and research.
Learn more: Research and Progress