Alzheimer’s disease is a progressive brain disorder that gradually affects memory, thinking, behaviour and a person's ability to carry out everyday activities.
It is the most common cause of dementia.
Dementia is not one specific disease. It is a general term describing a decline in memory, thinking and other cognitive abilities severe enough to interfere with everyday life.
According to the World Health Organization, approximately 57 million people worldwide were living with dementia in 2021, with more than 60% living in low- and middle-income countries.
Alzheimer’s disease is estimated to account for approximately 60–70% of dementia cases.
Although Alzheimer’s becomes more common with increasing age, it is important to understand that dementia is not an inevitable or normal part of ageing.
What Is Alzheimer’s Disease?
Alzheimer’s disease causes progressive changes within the brain.
These changes can begin many years before obvious memory or thinking problems become noticeable.
Over time, nerve cells—called neurons—lose their ability to function properly, lose connections with other neurons and eventually die.
As increasingly important brain networks become affected, symptoms become more severe.
The disease can eventually interfere with communication, movement, swallowing and the ability to perform basic activities without assistance.
What Happens in the Brain With Alzheimer’s Disease?
Alzheimer’s disease involves several complex biological processes.
Two of its best-known features are abnormal changes involving proteins called beta-amyloid and tau.
Amyloid Plaques
Beta-amyloid is formed from the breakdown of a larger protein.
In Alzheimer’s disease, abnormal beta-amyloid can accumulate between neurons, forming deposits known as amyloid plaques.
Scientists continue to investigate exactly how different forms of beta-amyloid contribute to disease progression.
Tau Tangles
Healthy neurons contain an internal transport system that helps move nutrients and other essential materials.
A protein called tau normally helps stabilise part of this system.
In Alzheimer’s disease, abnormal chemical changes cause tau to detach and accumulate within neurons, forming structures called neurofibrillary tangles.
These changes interfere with normal cellular function.
Loss of Neurons and Connections
Alzheimer’s also involves inflammation, disruption of communication between neurons and progressive loss of nerve cells and their connections.
As damage spreads through the brain, affected areas can shrink.
However, Alzheimer’s is much more complicated than simply having “plaques and tangles,” and researchers continue to investigate the biological processes responsible for the disease.
What Are the Early Symptoms of Alzheimer’s Disease?
Symptoms vary between individuals.
Memory problems are often among the first noticeable signs, particularly difficulty remembering recently learned information.
Early symptoms may include:
- forgetting recent conversations or events
- repeatedly asking the same questions
- frequently misplacing belongings
- difficulty remembering appointments
- problems finding familiar words
- becoming confused about dates or places
- difficulty planning or solving problems
- trouble managing money or paying bills
- taking longer to complete familiar tasks
- reduced judgement or decision-making ability
- becoming lost in familiar surroundings
- changes in mood, personality or behaviour.
One isolated episode of forgetfulness does not mean someone has Alzheimer’s disease.
The important concern is a persistent or worsening change from the person's previous abilities, particularly when it begins interfering with everyday life.
Normal Ageing or Alzheimer’s Disease?
Occasional forgetfulness can occur with normal ageing.
For example, someone may temporarily forget where they put their keys but later remember.
Alzheimer’s disease produces more persistent and progressive problems.
Someone might repeatedly place objects in unusual locations and be unable to retrace their steps, repeatedly forget important recent conversations, become lost in familiar places or increasingly struggle with activities they previously managed independently.
Ageing itself does not automatically lead to dementia.
Many people remain cognitively healthy into very old age.
Mild Alzheimer’s Disease
During the mild or early stage, a person may remain largely independent but increasingly experience difficulties.
These can include:
- memory loss that disrupts everyday life
- repeating questions
- forgetting recently learned information
- poor judgement
- problems handling finances
- difficulty planning or solving problems
- losing track of dates or locations
- misplacing belongings
- becoming lost
- taking longer to perform routine activities
- changes in initiative, mood or personality.
This is often the stage when Alzheimer’s disease is diagnosed.
Moderate Alzheimer’s Disease
As Alzheimer’s progresses, greater supervision and assistance are usually required.
Symptoms can include:
- increasing memory loss and confusion
- forgetting parts of personal history
- difficulty recognising some family members or friends
- problems learning new information
- difficulty reading, writing or working with numbers
- problems organising thoughts
- shortened attention span
- difficulty dressing or completing other multistep activities
- changes in sleeping patterns
- agitation or restlessness
- wandering
- anxiety
- suspiciousness or paranoia
- hallucinations or delusions in some people
- inappropriate or impulsive behaviour.
Caring needs generally increase substantially during this stage.
Severe Alzheimer’s Disease
In advanced Alzheimer’s disease, a person becomes increasingly dependent on other people for care.
Symptoms can include:
- severe communication difficulties
- inability to recognise surroundings
- major physical decline
- difficulty walking or moving independently
- difficulty swallowing
- loss of bladder or bowel control
- reduced interest in eating
- weight loss
- increased sleeping
- inability to perform basic personal care.
Swallowing difficulties can increase the risk of food or liquid entering the lungs, potentially causing aspiration pneumonia.
What Causes Alzheimer’s Disease?
There is no single cause that explains every case.
Alzheimer’s disease is thought to result from complex interactions between age-related brain changes, genetics, health conditions, lifestyle and environmental factors.
For most people, researchers cannot identify one specific event that caused the disease.
Is Alzheimer’s Disease Genetic?
Genes can influence Alzheimer's risk, but genetics does not have the same role in every case.
Some genetic variants increase susceptibility without guaranteeing that a person will develop Alzheimer's disease.
One well-known example is APOE ε4, which increases the risk of developing Alzheimer's and is associated with developing the disease at a younger age in some populations.
But carrying APOE ε4 does not mean a person will definitely develop Alzheimer’s disease, and people without it can still develop the condition.
Rare genetic mutations can directly cause inherited forms of Alzheimer’s disease.
These cases account for only a small proportion of all Alzheimer's disease.
Having a parent or sibling with Alzheimer’s may increase risk, but family history does not make the disease inevitable.
Anyone considering predictive genetic testing should discuss the implications with an appropriately qualified healthcare professional or genetic counsellor.
Age Is the Strongest Known Risk Factor
Age is the strongest known risk factor for Alzheimer's disease.
Most people diagnosed with Alzheimer’s are older adults.
Alzheimer's can occur earlier.
When symptoms develop before age 65, the condition is commonly referred to as younger-onset or early-onset Alzheimer's disease.
Although uncommon, some genetically determined cases can begin much earlier in adulthood.
Most importantly, Alzheimer’s should never be dismissed simply as an unavoidable consequence of getting older.
Other Factors Associated With Dementia Risk
Modern dementia research increasingly recognises that brain health is influenced throughout life.
The World Health Organization's updated 2026 guidelines on reducing cognitive decline and dementia risk address potentially modifiable factors involving health, behaviour and the environment.
Important factors associated with dementia risk include:
- high blood pressure
- diabetes
- physical inactivity
- tobacco use
- harmful alcohol use
- social isolation
- hearing problems
- high cholesterol
- obesity
- depression
- traumatic brain injury
- air pollution
- some aspects of visual impairment
- other cardiovascular and metabolic risks.
Not everyone with these risk factors develops dementia, and people without obvious risk factors can still develop Alzheimer's disease.
Risk is not destiny.
Can Alzheimer’s Disease Be Prevented?
There is currently no guaranteed way to prevent Alzheimer’s disease.
However, there is increasingly strong evidence that addressing modifiable risk factors across life can reduce or delay some cases of dementia.
In its updated 2026 guidance, WHO reports that up to 45% of dementia risk may be attributable to potentially modifiable risk factors.
This does not mean 45% of every individual's personal risk can simply be eliminated.
It means that, at the population level, addressing important modifiable factors could potentially prevent or delay a substantial proportion of dementia cases.
Ways to Support Brain Health and Reduce Dementia Risk
Evidence-based risk reduction involves overall health rather than a miracle food, supplement or brain-training product.
Stay Physically Active
Regular physical activity supports cardiovascular health and is associated with better brain health.
Adults should aim to follow physical-activity recommendations appropriate to their age, health and ability.
Walking, cycling, swimming, dancing and other forms of movement can all contribute.
Do Not Smoke
Tobacco use is associated with numerous diseases and is also a modifiable dementia risk factor.
People who smoke can benefit from evidence-based help to stop.
Avoid Harmful Alcohol Use
Heavy or harmful alcohol consumption can damage the brain and is associated with dementia risk.
If you drink alcohol, follow appropriate health guidance for your circumstances and country.
Manage High Blood Pressure
High blood pressure is an important cardiovascular risk factor and is also associated with cognitive decline and dementia.
Have your blood pressure checked appropriately and follow treatment recommendations if hypertension is diagnosed.
Manage Diabetes
Diabetes is associated with increased dementia risk.
People with diabetes should work with healthcare professionals to manage blood glucose, blood pressure, cholesterol and other cardiovascular risks.
Manage Cholesterol and Cardiovascular Health
What benefits the cardiovascular system can also be important for brain health.
Appropriate management of cholesterol and other cardiovascular risk factors forms part of a broader dementia-risk-reduction strategy.
Eat a Healthy Diet
A healthy dietary pattern emphasising vegetables, fruits, whole grains, legumes, nuts and other nutrient-rich foods can support cardiovascular and overall health.
No individual food has been proven to prevent Alzheimer's disease.
Be cautious of products claiming that particular berries, oils, vitamins or supplements can “stop dementia.”
Protect Your Hearing
Hearing loss is associated with dementia risk.
People experiencing hearing problems should consider appropriate assessment and management.
Stay Socially Connected
Social isolation has been associated with poorer health and dementia risk.
Maintaining meaningful relationships, community participation and social engagement may contribute to healthy ageing.
Protect Your Head
Traumatic brain injury is associated with increased dementia risk.
Use appropriate protective equipment during work, sport and travel, follow road-safety practices and take steps to reduce falls where relevant.
Address Depression and Mental Health
Depression and dementia have a complicated relationship.
Persistent depression should be properly assessed and treated rather than assumed to be a normal part of ageing.
Reduce Exposure to Air Pollution Where Possible
Air pollution has increasingly been recognised as a potential contributor to dementia risk.
Individuals cannot always control environmental exposure, which is why dementia prevention also requires broader public-health and environmental policies.
Can Vitamins or Supplements Prevent Alzheimer’s?
No vitamin, herbal remedy or dietary supplement has been established as a guaranteed way to prevent Alzheimer's disease.
Be particularly cautious about supplements advertised as:
- “memory cures”
- “brain detoxes”
- “Alzheimer’s prevention pills”
- “plaque removers”
- “natural dementia cures.”
Some products may interact with prescription medicines or cause adverse effects.
Treat genuine nutritional deficiencies when they exist, but do not assume that taking large doses of vitamins will prevent dementia.
When Should Memory Problems Be Checked?
Seek medical assessment when memory or thinking changes are:
- becoming progressively worse
- affecting work or everyday responsibilities
- interfering with finances or medication management
- causing someone to become lost
- affecting communication
- producing significant changes in personality or behaviour
- noticed consistently by family members or friends.
Early assessment matters because Alzheimer’s is not the only possible explanation for cognitive symptoms.
Other Conditions Can Cause Memory Problems
Memory and concentration difficulties can sometimes result from conditions other than dementia.
Examples can include:
- depression
- sleep disorders
- medication side effects
- thyroid disorders
- vitamin deficiencies
- infections
- alcohol or substance-related problems
- some neurological disorders.
Some causes may be treatable.
This is another reason not to diagnose Alzheimer’s based solely on symptoms seen online.
How Is Alzheimer’s Disease Diagnosed?
There is no single routine assessment that should be interpreted in isolation.
Evaluation may involve:
- a detailed medical history
- information from family or someone who knows the person well
- physical examination
- neurological examination
- cognitive and memory testing
- assessment of the person's ability to carry out everyday activities
- blood tests to investigate other possible causes
- brain imaging such as MRI or CT in appropriate cases.
Specialist assessment may include additional testing.
Biomarkers and Alzheimer's Diagnosis
Alzheimer's diagnosis has changed significantly as scientists have developed ways of detecting biological signs of the disease.
Specialist investigations may include PET imaging or analysis of cerebrospinal fluid for Alzheimer-related biomarkers.
Blood-based biomarker tests measuring proteins associated with amyloid and tau are also advancing rapidly and are becoming available in some healthcare systems.
However, availability and approved clinical use vary by country.
A blood test should not be interpreted independently of a proper clinical assessment.
Is There a Cure for Alzheimer’s Disease?
There is currently no cure that reverses Alzheimer’s disease.
However, treatment has advanced significantly.
Some medicines can help manage cognitive symptoms, while newer disease-modifying treatments can slow disease progression in carefully selected people with early Alzheimer's disease.
Treatment decisions require individual medical assessment.
Medicines for Alzheimer’s Symptoms
Medicines used in appropriate patients can include cholinesterase inhibitors, such as:
- donepezil
- rivastigmine
- galantamine.
Another medicine, memantine, may be used in some people with moderate-to-severe Alzheimer's disease.
These medicines do not cure Alzheimer's, but they may help some people manage cognitive and functional symptoms for a period of time.
Newer Disease-Modifying Treatments
A major change in Alzheimer's treatment has been the development of medicines targeting amyloid in the brain.
Examples include lecanemab and donanemab, which have been authorised in some countries for selected people with early Alzheimer's disease.
These treatments are not cures.
They can modestly slow clinical decline in appropriate patients, but they require careful patient selection and monitoring because potentially serious side effects can occur, including amyloid-related imaging abnormalities (ARIA) involving brain swelling or bleeding.
Access, regulatory approval and eligibility vary substantially between countries.
Anyone considering these treatments needs assessment by an appropriate specialist.
Living With Alzheimer’s Disease
Good Alzheimer's care involves much more than medication.
Depending on the stage of disease, helpful approaches can include:
- maintaining predictable routines
- making the home environment safer
- supporting appropriate physical activity
- encouraging social engagement
- managing other medical conditions
- supporting adequate food and fluid intake
- reviewing medicines regularly
- addressing sleep problems
- planning for increasing care needs
- providing support for family members and caregivers.
People living with Alzheimer's should continue to be treated with dignity and included in decisions about their lives for as long as possible.
Supporting Caregivers
Alzheimer’s affects families and caregivers as well as the person diagnosed.
Caring responsibilities can become physically, emotionally and financially demanding.
Caregivers should not be expected to manage everything alone.
Depending on local availability, support may come from:
- family and friends
- healthcare professionals
- dementia organisations
- community services
- respite care
- caregiver support groups
- social-care services.
Seeking help is an important part of sustainable dementia care.
The Bottom Line
Alzheimer’s disease is a progressive brain disorder and the most common cause of dementia.
Memory loss is often an early symptom, but Alzheimer's can also affect language, judgement, problem solving, orientation, mood, behaviour and eventually physical functioning.
Increasing age is the strongest known risk factor, but Alzheimer’s disease is not a normal or inevitable part of ageing.
There is currently no guaranteed method of preventing Alzheimer's and no cure that reverses established disease.
However, current evidence indicates that addressing modifiable dementia risk factors—including physical inactivity, smoking, harmful alcohol use, high blood pressure, diabetes, social isolation and other health and environmental factors—may reduce or delay some dementia.
And treatment is evolving. Alongside medicines that help manage symptoms, newer disease-modifying therapies can slow progression in some carefully selected people with early Alzheimer's disease.
Anyone experiencing persistent or worsening changes in memory, thinking or behaviour should seek appropriate medical assessment rather than assuming that the changes are simply part of getting older.
Medical Disclaimer
This article provides general educational information and is not a substitute for diagnosis or personalised medical advice from an appropriately qualified healthcare professional. Memory problems can have many possible causes. Anyone experiencing persistent or worsening cognitive changes should seek professional assessment. Availability and approval of Alzheimer's diagnostic tests and treatments vary between countries.
Sources and Further Reading
World Health Organization — Dementia
https://www.who.int/health-topics/dementia
World Health Organization — Risk Reduction of Cognitive Decline and Dementia: Guidelines, Second Edition (2026)
https://www.who.int/publications/i/item/9789240123557
World Health Organization — 2026 Dementia Risk-Reduction Guidelines Announcement
https://www.who.int/news/item/15-07-2026-new-who-guidelines--up-to-45--of-dementia-risk-could-be-prevented-or-delayed
National Institute on Aging — Alzheimer's Symptoms and Diagnosis
https://www.nia.nih.gov/health/alzheimers-symptoms-and-diagnosis
National Institute on Aging — What Are the Signs of Alzheimer's Disease?
https://www.nia.nih.gov/health/alzheimers-symptoms-and-diagnosis/what-are-signs-alzheimers-disease
National Institute on Aging — Alzheimer's and Dementia
https://www.nia.nih.gov/health/alzheimers-and-dementia
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