What Is Alzheimer’s Disease?

Learn the early signs and symptoms of Alzheimer's Disease

Click here to review the 10 warning signs from the Alzhemier's Association

Alzheimer’s disease is the most common cause of dementia in older adults. It is a progressive disorder that causes brain cells to waste away (degenerate) and die.

Nearly 6 million Americans are living with Alzheimer’s disease. Unless an effective treatment or cure is identified, this number is projected to more than double by the year 2050.


Dementia is not a specific disease. It is a condition where problems with memory, thinking, or behavior interfere with our ability to perform daily activities safely and independently. We all forget sometimes, and it is normal for people to become more forgetful as we get older. Who hasn’t misplaced their keys, forgotten a medication dose, or forgotten to pay a bill at one time or another? But dementia is not a part of normal aging. In dementia, problems in memory and thinking abilities become severe enough to cause problems carrying out responsibilities of daily life and make it difficult to remain independent.


Alzheimer's disease is the most common cause of dementia in older adults, but it is only one type of dementia. Other conditions can also cause memory loss.

The dementia of Alzheimer’s disease is caused by the build-up of proteins in and around brain cells that form clumps and tangles, causing the cells to malfunction and die. The two specific proteins in AD are amyloid (which form clumps or “plaques” outside of brain cells) and tau (which forms tangles of disintegrating cell parts inside brain cells). These changes typically start in the memory center of the brain, which is why memory loss is often an early symptom in Alzheimer’s disease.

In Alzheimer's disease, amyloid plaques form around cells and make it hard for neurons to communicate with each other. Source: Alzheimer’s Association

In normal brains, tau holds cell components together, but in Alzheimer’s disease the tau comes loose, forming threads that tangle together. These changes interfere with the neuron’s ability to function. Source: National Institute on Aging Alzheimer’s Disease Education and Referral Center

Alzheimer’s disease is called a “neurodegenerative” dementia because the build-up of proteins does not stop, brain cells continue to die, and symptoms continue to worsen gradually over time. Although memory loss is usually the first and most prominent symptom, over time Alzheimer's disease can impact communication, problem solving, way-finding, mood, and behavior. In some less common forms of Alzheimer's disease, cell changes start in other areas of the brain, causing problems with other thinking abilities to show up first.

Learn the 10 Early Signs of Alzheimer's, as compiled by the Alzheimer's Association.


This brief video, from the National Institute on Aging shows how Alzheimer's disease causes changes in the brain that result in difficulties with memory, thinking, and behavior. It also shows how some very important work is being done to find a way to delay or prevent the onset of disease.


Mild cognitive impairment (MCI) is a condition where a decline in memory, thinking, or behavior has occurred, but it is not severe enough to cause problems managing responsibilities of daily life independently. The decline is not due to a known condition such as a stroke, head injury, or brain tumor.

People with MCI are at increased risk of developing Alzheimer's disease or AD-related disorder, but a diagnosis of MCI does not mean the person will definitely go on to develop dementia. Some people with MCI do not get worse over time, and a few even get better (if their cognitive change is due to other conditions that are identified and treated).


Many conditions can cause someone to experience problems with memory, thinking, or behavior to the degree that they have trouble performing daily activities safely and independently.

Other neurodegenerative conditions include Lewy body dementia and frontotemporal dementia. Like Alzheimer's disease, these disorders are caused by abnormal proteins in the brain. Early symptoms typically differ from Alzheimer's because the regions of the brain that are first and most affected by the proteins are outside the memory center. In Lewy body dementia, problems start in the parts of the brain controlling attention, movement, and alertness. In frontotemporal dementia, early changes are seen in the parts of the brain that control our behavior and/or our ability to communicate.

Vascular dementia is the 2nd most common type of dementia and is caused by strokes or other problems with blood vessels that supply nutrients to the brain.

Infections, thyroid disorders, blood sugar problems, nutrition deficiencies, medications, and brain tumors are medical conditions that can cause dementia that may improve with treatment.

Other conditions such as sleep disorders, stress, depression, anxiety, and chronic pain can also contribute to memory loss. Memory may return to normal when these conditions are treated and controlled.


  • Mayo Clinic ADRC online resources for people with Alzheimer’s Disease or AD-related disorders and their families.