What is Alzheimer’s disease?

Reviewed by Chimene Richa, MD, 

Reviewed by Chimene Richa, MD, 

last updated: Aug 15, 2022

6 min read

Everyone has moments where they enter a room and forget why they walked in, search frantically for their keys or phone that’s right in their pocket, or can’t remember the password for their email account. Occasional memory lapses are common, especially when we’re stressed out or have other things occupying our minds. 

But if one’s memory is consistently impaired and this starts disrupting daily life, it may be a sign of a brain condition, like Alzheimer’s disease, the most common cause of dementia. 


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What is Alzheimer’s disease? 

Alzheimer’s disease (AD) is a neurological (brain) condition. AD is a type of dementia, a group of conditions that affect memory, thought processes, and the level of independence in daily life. AD behavioral symptoms may start slowly and subtly, but they usually worsen over time. Brain conditions that get worse over time are called neurodegenerative diseases, and Alzheimer’s is one of them (Kumar, 2021). 

How common is Alzheimer’s disease? 

Alzheimer’s disease is the most common form of dementia, and the number of Americans living with the disease is growing fast. According to the latest data from the Alzheimer’s Association, 6.5 million people in the US over age 65 are living with Alzheimer’s in 2022. That means about 1 in 9 Americans over 65 has Alzheimer's (Alzheimer’s Association, 2022). 

This number is expected to increase significantly—to a projected 12.7 million by 2050—unless researchers find effective ways to prevent and treat it. 

Most people who get AD are over the age of 65, and it becomes more common with increasing age—in fact, the rate of AD is thought to double every ten years after age 60 (Prince, 2013; Alzheimer’s Association, 2022).

In some people, AD may occur at a younger age (early onset AD), but this is rare (Rossor, 2010).

Do memory problems always mean Alzheimer’s disease?

The answer is no. Forgetting things can be a normal part of aging, and even young adults have an occasional memory slip. Needing a little longer to learn new things or occasionally losing one’s glasses or keys are usually signs of mild, normal forgetfulness, rather than serious memory problems.

In other words, forgetting where you put your keys can be normal. But losing track of dates and seasons or how to do daily tasks could be early signs of a problem with the brain tissue.

It’s a good idea to talk to your healthcare provider if you’re worried about your own or a loved one’s memory. They can evaluate whether memory problems are normal and what may be causing them.

Symptoms and stages of Alzheimer’s disease

When it comes to signs of Alzheimer’s disease, they don’t appear all at once, and it can take some time until symptoms become noticeable. There are typically three main stages of AD (Breijyeh, 2020): 

  • Early-stage, or mild AD

  • Middle-stage, or moderate AD

  • Late-stage, or severe AD

The changes typically start in the part of the brain that affects learning, which explains why one of the most common early symptoms is difficulty remembering newly learned information. Many people with AD experience memory problems as early as 15 years before their diagnosis but may not notice because the changes are initially subtle (Verlinden, 2016). 

Common symptoms of Alzheimer’s during the early or mild phases include (Kumar, 2021; Breijyeh, 2020):

  • Memory loss: This usually affects short-term memory (memory of recent events) more than long-term memory. This means that people with AD may remember things that happened during childhood more easily than something that happened the day before. 

  • Having a hard time concentrating

  • Difficulty problem solving

  • Disorientation (forgetting the month, day, time, etc.)

  • Mood swings

  • Depression

  • Difficulty multitasking

As Alzheimer’s disease progresses, the symptoms often worsen and interfere more with daily life. The moderate and late stages of AD include symptoms like (Kumar, 2021; Breijyeh, 2020):

  • Difficulty recognizing family and friends

  • Difficulty reading and writing

  • Loss of motivation

  • Impaired judgment

  • Language difficulty and trouble expressing oneself (aphasia)

  • Difficulty with motor skills or performing movements and tasks (apraxia)

  • Trouble recognizing and identifying objects, persons, or sounds (agnosia)

  • Difficulty with depth perception and distance perception (visuospatial skills)

  • Social withdrawal and apathy

  • Behavior changes 

  • Agitation and irritability

  • Sleep disturbances

  • Psychosis

What causes Alzheimer’s disease?

Scientists still don’t know a ton about the causes of Alzheimer’s disease. We do know that complex brain changes cause the symptoms of the disease, but what triggers them and the characteristics of these changes aren’t fully understood. 

At a basic level, there’s evidence that changes in the brains of people with the disease are in part caused by the abnormal build-up of certain proteins in the brain. Studies have shown that a protein called amyloid clumps together and forms plaques in the brains of people with AD. A second protein called Tau accumulates inside nerve cells and leads previously healthy neurons to stop functioning. Eventually, these protein build-ups block the communication between nerve cells, injure the nerve cells and lead to these brain cells dying (Bloom, 2014). 

Besides protein build-up, many other complex brain changes, such as inflammation and problems that affect blood vessels, are thought to play a role in Alzheimer’s as well. It is unclear what triggers all of these brain changes, but there are multiple possible causes, including genetic, environmental, and lifestyle factors. 

Risk factors for Alzheimer’s disease

Though there’s no way to prevent AD, some factors may put some people at greater risk of developing it. Risk factors for AD include: 

  • Family history: Genetics plays a role in many medical conditions. Families with certain specific genes like Apolipoprotein E (ApoE) are at higher risk for developing AD, though it’s not clear if it’s just due to the genes or the fact that families share similar environmental risk factors (Vardarajan, 2014).  

  • High blood pressure: Blood vessel injury is a potential cause of AD, so people with conditions like high blood pressure that stress blood vessels may be at increased risk for developing AD (Gottesman, 2017).   

  • High cholesterol: Some data suggests that having a history of high cholesterol or difficulty regulating cholesterol levels may contribute to AD (Leduc, 2010). 

  • Diabetes and obesity: Diabetes and obesity are closely linked since people with obesity are more likely to develop type 2 diabetes. But it turns out that each of these conditions may also increase the risk of developing AD (Profenno, 2010).  

  • Sedentary lifestyle: Studies suggest that a sedentary lifestyle without much physical activity may increase the risk of developing AD (Rolland, 2008).  

  • Smoking: There’s evidence that heavy smoking, especially during mid-life, may be linked to a higher risk of developing AD (Rusanen, 2011).  

  • Head trauma: Trauma and head injuries may increase inflammation and amyloid plaques that contribute to developing AD (Heneka, 2015). 

  • Strokes (cerebrovascular disease): People who have had strokes, even small ones that may have been undetected, may be at higher risk of developing AD. A small study found that on autopsy, people diagnosed with AD were likely to have evidence of previous strokes (Chui, 2006). 

How do you diagnose Alzheimer’s disease? 

If someone has signs or symptoms of AD, the first step is to speak to a healthcare professional. They will take a thorough medical history and perform a physical and psychiatric examination to determine if another health condition is causing or contributing to a person's symptoms. 

In order to diagnose Alzheimer’s disease, the condition must (McKhann, 2011): 

  • Interfere with the person’s daily activities

  • Interfere with the person’s thought processes, thinking skills, learning, and judgment (cognitive impairment)

  • Be a change from the person’s previous state

  • Not be caused by another underlying condition 

There are many different screening tools a healthcare provider can use to test memory and thought processes (cognitive function). One screening tool, the mini mental status exam (MMSE), is a quick and easy screen but may miss AD in the early phase. A second commonly used test is the Montreal Cognitive Assesment, or MoCA. The MoCA may be more effective than the MMSE, since it can identify people who are mildly affected (Pinto, 2019).  

Brain scans like MRIs can show brain lesions and changes that occur in some people with AD, which can be helpful in supporting an Alzheimer’s diagnosis. Brain images can also rule out other possible causes of cognitive symptoms, like strokes (Chandra, 2019). 

Healthcare providers often repeat the tests just mentioned to help determine how the person’s memory and other cognitive functions are changing over time.

How do you treat Alzheimer’s disease? 

There’s currently no cure for Alzheimer’s disease. There are, however, medications to treat AD symptoms. There are two main types of medication, acetylcholinesterase inhibitors and NMDA antagonists, that help people with Alzheimer’s manage their symptoms (Cummings, 2019).

  • Acetylcholinesterase inhibitors block the enzyme acetylcholinesterase, increasing the amount of acetylcholine in the brain. Nerve cells use acetylcholine to communicate, so higher levels of acetylcholine may improve cognitive function. 

  • NMDA antagonists block the NMDA receptor and regulate the effects of a neurotransmitter called glutamate.

Researchers are continuing to identify new possibilities for drugs to manage AD. For example, in 2021, a new drug named aducanumab entered the stage, and the US Food and Drug Administration (FDA) granted it accelerated approval. In clinical trials, this drug reduced amyloid deposits in the brain—the kind of protein deposits seen in the brains of people with AD (FDA, 2021).

While that sounds promising, there’s some uncertainty about whether the drug actually slows down the progression of cognitive decline. For now, the drug is approved for people with early Alzheimer’s disease. Medicare will cover aducanumab, which costs around $28k per year, only for people who receive it as participants in a clinical trial.

Being diagnosed with a condition like Alzheimer’s disease may feel disheartening. But there are ways to treat your symptoms and resources you can use to help identify the best options for you. Talking to your healthcare provider about AD may be your best first step. 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

August 15, 2022

Written by

Felix Gussone, MD

Fact checked by

Chimene Richa, MD

About the medical reviewer

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.