Alzheimer's disease is a progressive degenerative disorder that becomes worse over time. It involves a gradual loss of memory, as well as changes in behavior, thinking, and language skills.

Alzheimer's disease is the most common form of dementia. It affects more than 5 million people in the United States.

Although every person experiences Alzheimer's differently, the way in which the disease progresses can be grouped into a series of stages.

It is important to make sure that someone with dementia lives well with the condition and that their needs are met, rather than focusing on what stage they might be in.

How quickly does Alzheimer's disease progress?

Alzheimer's seems to develop slowly compared with other types of dementia, but the rate of progression varies between individuals.

In comparison to other types of dementia, Alzheimer's may develop slower. Regular exercise and staying active may help to maintain abilities for a longer time.

The average life expectancy for a person with this disease is 8-10 years after diagnosis, but people can live with Alzheimer's for 20 years or more.

Several factors can affect disease progression.

• Age: People with Alzheimer's symptoms that develop before age 65 years may have faster progression
• Genes: A person's genes may affect progression rate
• Physical health: People with poorly managed heart conditions or diabetes, who have had several strokes, or have repeated infections, may deteriorate quicker

Keeping active, being involved in activities, and getting regular exercise may help the individual to maintain their abilities for longer.

Other important factors include:

• Maintaining a healthy diet
• Getting enough sleep
• Taking all prescribed medication correctly
• Quitting smoking
• Not drinking too much alcohol
• Going to regular checkups

If a person with Alzheimer's disease experiences a sudden change in abilities or behavior, they could have another health problem or an infection. It is important to seek advice from a doctor as soon as possible.

Stages of Alzheimer's disease

Looking at Alzheimer's in stages can give a clearer idea of the changes that could occur.

Stages are a rough guide. The symptoms a person has, and when they appear, will vary. There are several different ways of mapping Alzheimer's disease. Some people refer to seven stages, while others refer to just three.

This article, however, will look at five stages of Alzheimer's disease:

1. Preclinical Alzheimer's disease
2. Mild cognitive impairment due to Alzheimer's disease
3. Mild dementia due to Alzheimer's disease
4. Moderate dementia due to Alzheimer's disease
5. Severe dementia due to Alzheimer's disease

The dementia noted in stages 3 to 5 describes the set of symptoms that affect memory, thinking, problem-solving or language, and they are severe enough to affect daily life.

The average time between the onset of Alzheimer's symptoms and reaching a diagnosis is approximately 2.8 years.

Stage 1: Preclinical Alzheimer's disease

The functional changes that are associated with Alzheimer's are thought to begin years, or even decades, before diagnosis.

This long phase is known as the preclinical stage of Alzheimer's disease. During this stage, there will not be any noticeable clinical symptoms.

Although there are no noticeable symptoms in the preclinical stage, imaging technologies can spot deposits of a protein called amyloid beta.

In people with Alzheimer's disease, this protein clumps together and forms plaques. These protein clumps may block cell-to-cell signaling and activate immune system cells that trigger inflammation and destroy disabled cells.

There are other biological markers, or biomarkers, that show an increased risk of disease, as well as genetic tests that can detect if a person does have an increased risk.

Using imaging technology to locate amyloid beta clumps, biomarker detection, and genetic testing could all be important in the future as new Alzheimer's treatments are developed.

Researchers are studying this preclinical stage to work out which factors can predict the risk of progression from normal cognition to stage 2 of Alzheimer's progression, which involves mild cognitive impairment.

Researchers are also hoping that their studies will help people with Alzheimer's get treated at a much earlier stage.

Disease-modifying therapies may be most effective in the more initial stages of Alzheimer disease, and they could slow disease progression.

Stage 2: Mild cognitive impairment due to Alzheimer's disease

Mild cognitive impairment occurs between the cognitive decline that is expected as a normal part of aging, and the most severe decline of dementia.

A person with mild cognitive impairment may notice subtle changes in their thinking and their ability to remember things. They may exhibit memory lapses when it comes to recent conversations they have had, recent events, or appointments they have been to.

However, changes to memory and thinking at this stage are not serious enough to cause problems with day-to-day life or usual activities.

As people age, it is normal for forgetfulness to increase slightly, or for individuals to take longer to think of a word or remember a name. If the problem is more severe, it could be a sign of mild cognitive impairment.

Symptoms of mild cognitive impairment include:

• Forgetting things more often
• Forgetting appointments, conversations, or recent events
• Inability to make decisions or feeling overwhelmed when doing so
• Becoming increasingly unable to judge the time or sequence of steps to complete a task
• Being more impulsive or showing increasingly poor judgment
• Friends and family noticing the above changes

People with mild cognitive impairment might also experience depression, irritability, aggression, apathy, and anxiety.

Not everyone with mild cognitive impairment will develop dementia. Research suggests that around 10-15 percent of older adults with mild cognitive impairment will develop dementia each year.

There are currently no drugs or therapies specifically approved that are able to treat mild cognitive impairment.

However, studies are underway to identify treatments that may help to improve symptoms, or prevent or delay their progression to dementia.

Stage 3: Mild dementia due to Alzheimer's disease

The mild dementia stage is the typical point at which doctors would diagnose Alzheimer's disease.

In addition to friends and family noticing that the person is having problems with their memory and thinking, these problems may also begin to affect daily life.

Symptoms of mild dementia due to Alzheimer's disease include:

• Difficulty remembering newly learned information
• Asking the same question repeatedly
• Trouble problem-solving and completing tasks
• Reduced motivation to complete tasks
• Experiencing a lapse in judgment
• Becoming withdrawn or uncharacteristically irritable or angry
• Having difficulty finding the correct words to describe an object or idea
• Getting lost or misplacing items

Stage 4: Moderate dementia due to Alzheimer's disease

During the stage of moderate dementia due to Alzheimer's disease, the person becomes increasingly confused and forgetful. They may need help with daily tasks and assistance with looking after themselves.

Symptoms of moderate dementia due to Alzheimer's disease include:

• Losing track of location and forgetting the way, even in familiar places
• Wandering in search of surroundings that feel more familiar
• Failing to recall the day of the week or season
• Confusing family members and close friends, or mistaking strangers for family
• Forgetting personal information such as address, phone number, what schools they went to
• Repeating favorite memories or making up stories to fill in the gaps they have in their memory
• Needing help with making decisions of what to wear for the weather or season
• Needing assistance with bathing and grooming
• Occasionally losing control of bladder or bowel
• Becoming unduly suspicious of friends and family
• Seeing or hearing things that are not there
• Becoming restless or agitated
• Displaying aggressive or physical outbursts

Stage 5: Severe dementia due to Alzheimer's disease

During this stage, the person's mental functioning continues to decline. Movement and physical capabilities can worsen significantly.

Symptoms of severe dementia due to Alzheimer's disease include:

• Inability to speak and communicate coherently
• Needing complete assistance with personal care, eating, dressing, and using the bathroom
• Failure to walk without help, unable to sit, or hold head up
• Rigid muscles and abnormal reflexes
• Loss of the ability to swallow, inability to control bladder and bowel movements

A person with severe Alzheimer's disease has a high chance of dying from pneumonia. Pneumonia is a common cause of death in those with Alzheimer's because as the person loses the ability to swallow, food and beverages can enter the lungs and cause infection.

Other common causes of death among people with Alzheimer's disease can include dehydration, malnutrition, and other infections.

Alzheimer's disease is currently the sixth leading cause of death in the U.S. Around 1 in every 3 seniors die from Alzheimer's or another type of dementia. It kills more people than breast cancer and prostate cancer combined.

Life expectancy for individuals with Alzheimer's disease varies depending on many factors. If a person's symptoms appear when they are in their 60s or 70s, they are likely to live for 7-10 years. However, if a person's symptoms start in their 90s, they are likely to live for around another 3 years.

Among the top 10 leading causes of death in the U.S., Alzheimer's is the only disease that cannot be slowed down, cured, or prevented.

As the cause of Alzheimer's is unknown, there is no known way to prevent the disease. Research is ongoing. Medications to treat the disease can help for a while with memory symptoms and other such cognitive changes.

Actions that may contribute to the reduction of dementia risk - or possibly delay its onset - include quitting smoking, cutting down on alcohol, eating a healthy diet, maintaining a healthy weight, and staying physically fit and mentally active.