Alzheimer’s disease is a degenerative brain disease that causes progressive loss of memory — also known as dementia and impaired cognitive function — eventually leading to death. This disease isn’t the only form of dementia, but it’s the most common. Overall, Alzheimer’s accounts for 60 percent to 80 percent of dementia cases.

Alzheimer’s is most commonly diagnosed in people ages 65 and older. The disease’s effects are different from mild forgetfulness — say, sometimes struggling to remember a name or misplacing your keys. Some age-related memory loss can be a normal part of aging in older adults.

Our understanding of Alzheimer’s disease has come a long way in the 100 years since it was first identified. Alzheimer’s disease can’t be cured, but treatments can lessen symptoms and improve quality of life.

What Is Alzheimer’s Disease?

Alzheimer’s disease slowly changes the structure and function of the brain over time. It’s important to note that Alzheimer’s isn’t a mental illness. However, some people with Alzheimer’s may show signs of certain mental illnesses.

In Alzheimer’s disease, changes to the brain cause cognitive dysfunction, or dementia. Alzheimer’s is characterized by an abnormal buildup of two proteins in the brain — beta-amyloid and tau.

Beta-amyloid builds up between neurons (brain cells) to form plaques. Collections of tau proteins within brain cells form clumps or neurofibrillary tangles.

Beta-amyloid plaques and neurofibrillary tangles often begin in areas of the brain that control memory. From there, the proteins can spread throughout the brain. This is why memory problems are one of the earliest noticeable symptoms of Alzheimer’s.

As plaques and tangles spread, they destroy nerve cells and shrink brain tissue. The increase in brain damage eventually results in worsening symptoms. In the latest stage of Alzheimer’s disease, people lose the ability to function independently, which leads to death.

Alzheimer’s shares some overlap with other dementias and cognitive conditions. Protein plaques and tangles are sometimes seen in other neurodegenerative diseases like Parkinson’s disease.

People with Alzheimer’s are also sometimes diagnosed with other forms of dementia, including vascular dementia. People with Down syndrome are also at increased risk of developing Alzheimer’s disease.

What Causes Alzheimer’s?

The causes of Alzheimer’s disease aren’t well understood. Most cases are believed to be caused by a combination of genetics (family history), lifestyle, and environmental risk factors.

In some rare cases, the risk of Alzheimer’s is determined by inherited genes, such as a mutated (changed) presenilin-1 gene or a certain variant of the apolipoprotein E gene. Getting one of these genes from one of your parents means you may be more likely to develop the disease. This genetic risk accounts for less than 1 percent of cases. Most genetic Alzheimer’s cases lead to early-onset Alzheimer’s disease, which occurs in middle age.

How Common Is Alzheimer’s?

It’s estimated that more than 6 million people in the United States have Alzheimer’s disease. Alzheimer’s is currently the seventh leading cause of death among Americans.

How Does Alzheimer’s Progress?

Everyone diagnosed with Alzheimer’s experiences disease progression but in different ways. Some people progress faster than others. People with Alzheimer’s can experience mild or severe symptoms. These symptoms can appear earlier or later over the course of their disease.

Doctors use different staging systems to describe the progression of Alzheimer’s symptoms. These systems can have three, five, or seven stages.

People in the early stages of Alzheimer’s typically experience mild cognitive impairment (MCI) first. MCI is a type of dementia that causes noticeable memory or language problems. Those with MCI usually don’t have problems completing daily activities. Not everyone with MCI will go on to develop Alzheimer’s.

Alzheimer’s disease is believed to develop long before symptoms appear. Recent research has focused on identifying biomarkers, or proteins specific to Alzheimer’s. These biomarkers may help health care providers diagnose Alzheimer’s as early as possible. Common tests for biomarkers include MRI imaging and blood work. These tests look for early hallmarks of the disease.

Read more about how Alzheimer’s is diagnosed.

Is Alzheimer’s Reversible?

Unfortunately, Alzheimer’s disease isn’t reversible. It’s a progressive disease — once it begins, it keeps worsening over time. The brain changes that cause Alzheimer’s symptoms are permanent and can’t be undone. There are medications available to help slow cognitive decline, but it can’t be reversed.

What Is the Prognosis for Alzheimer’s?

Alzheimer’s is a fatal disease. According to the Alzheimer’s Association, most people survive for four to eight years after being diagnosed. Some people live as long as 20 years.

Recent advances in Alzheimer’s treatments can relieve symptoms and may slow disease progression. This is especially true when treatment begins in the early stages of the disease.

Read more about treatments for Alzheimer’s.

Why Do People Die From Alzheimer’s?

In people with late-stage Alzheimer’s, brain shrinkage makes it harder to regulate basic bodily functions. If a person loses the ability to swallow, they may need to be fed with a tube.

Aspiration pneumonia is the most common cause of death in people with Alzheimer’s disease. This occurs when a person accidentally inhales liquids or small pieces of food because they have trouble swallowing. The bacteria from the mouth or the food enter the lungs and start an infection.

Many people with Alzheimer’s disease are older, so their immune systems don’t work as well as they used to. Infections like aspiration pneumonia with Alzheimer’s are often fatal.

The History of Alzheimer’s

The medical community first became aware of Alzheimer’s disease a little over a hundred years ago. In the early 1900s, German psychiatrist and neuropathologist Alois Alzheimer observed a person with unexplainable memory loss, paranoia, and confusion. After their death, Alzheimer performed an autopsy. He identified what are now known as beta-amyloid plaques and neurofibrillary, or tau, tangles.

Several years later, Alzheimer was the first person to document different stages of the disease that bears his name. Later on, the invention of the electron microscope in 1931 allowed scientists to study the brain more.

Progress in Alzheimer’s Research

In the 1970s, Alzheimer’s disease began to receive more attention and resources for research. The National Institute on Aging (NIA) was established in 1974. The NIA funds Alzheimer’s research and has a database of current Alzheimer’s disease clinical trials. In 1976, Alzheimer’s was described as the most common form of dementia and a major public health challenge.

In the 1980s, scientists started looking for genes involved in Alzheimer’s disease. The first gene associated with Alzheimer’s disease was identified in 1987. Since then, researchers have continued to pinpoint genetic variants that raise the risk of developing Alzheimer’s.

Meanwhile, researchers from the University of California, San Diego identified beta-amyloid in 1984. Two years later, a group from New York identified tau protein — the main component of neurofibrillary tangles. Based on these findings, researchers began finding new ways to target these proteins with medications.

The Development of Treatments for Alzheimer’s

The first Alzheimer’s drug, tacrine (Cognex), was approved by the U.S. Food and Drug Administration (FDA) in 1993. This drug is now rarely prescribed due to its serious effects on the liver.

Eight medications currently are approved to treat Alzheimer’s disease. Cholinesterase inhibitors work by altering the function of a neurotransmitter called acetylcholine. Examples include:

• Donepezil (Aricept)
• Rivastigmine (Exelon)
• Galantamine (Razadyne)

Memantine (Namenda) is a type of drug called an N-methyl-D-aspartate (NMDA) receptor antagonist. This medication works by altering chemical messengers in the brain. Memantine may help improve memory, language, and attention.

Namzaric is a combination of donepezil and memantine. Doctors use this medication to treat moderate to severe Alzheimer’s disease.

The FDA has also approved two amyloid-targeting therapies. Lecanemab-irmb (Leqembi) and aducanumab-avwa (Aduhelm) are antibody (protein) drugs. They help remove beta-amyloid proteins from the brain. Lecanemab was approved in 2023, while aducanumab has been around since 2021. The company that manufactures aducanumab is discontinuing the drug in 2024.

Alzheimer’s disease can cause behavioral and psychological symptoms like agitation and hallucinations. In 2023, the FDA approved brexpiprazole (Rexulti), the first treatment for agitation due to Alzheimer’s disease.

The first major clinical trial for the prevention of Alzheimer’s disease was launched in 2009. Sponsored by the Dominantly Inherited Alzheimer Network, the ongoing trial is testing a drug therapy in people who inherited a genetic mutation that puts them at high risk of the disease. Researchers hope to conclude the study in July 2024.

Talk With Others Who Understand

On myALZteam, the social network for people with Alzheimer’s and their loved ones, more than 85,000 members come together to ask questions, give advice, and share their stories with others who understand life with Alzheimer’s.

Are you or a loved one living with Alzheimer’s disease? Share your experience in the comments below, or start a conversation by posting on your Activities page.