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What is the difference between dementia and Alzheimer’s disease?

Dementia vs Alzheimer's

Dementia can be caused by many different diseases – not just Alzheimer's – all of which affect the brain in different ways. Most often, these changes will show up as a decline in cognitive abilities such as thinking, problem solving and memory, as well as differences in mood and behaviour.

Alzheimer’s disease starts in the brain many years before symptoms start to show. Most people who develop Alzheimer’s will do so when they are over 65 years old.  Early symptoms are mild and so don’t stop someone doing their normal everyday activities. It’s only later that symptoms become severe enough to be called ‘dementia’.  

Other common causes of dementia include vascular disease, which prevents blood from getting to the brain properly, and Lewy body disease.

What is dementia?

Dementia is a term used to describe problems with memory or thinking. These symptoms get worse over time, which is known as ‘cognitive decline’.  

Dementia is caused by disease in the brain. It is not a natural part of aging.  

The symptoms of dementia typically include: 

• memory loss  – for example, problems recalling things that happened recently
• confusion and needing help with daily tasks – for example, struggling to make decisions, solve problems or follow a series of steps (such as cooking a meal) – for example, difficulties following a conversation or finding the right word for something
• problems with language and understanding – for example, difficulties following a conversation or finding the right word for something
• changes in behaviour – for example, becoming unusually anxious, irritable or sad.

The condition varies a lot from person to person. Not everyone will have problems with memory during the early stages.

All types of dementia, including Alzheimer's disease, are progressive conditions. This means that its symptoms are mild at first but they get worse over time. Sadly, dementia is a terminal condition and is the most common cause of death in the UK. 

What is Alzheimer’s disease?

Alzheimer’s disease is the most common cause of dementia. About two out of three people living with dementia in the UK have Alzheimer’s disease, which is sometimes called 'Alzheimer’s'.
 
Alzheimer’s disease is a physical illness which damages a person’s brain. It starts many years before symptoms start to show.
 
Early symptoms of Alzheimer’s are mild and don’t prevent someone from doing everyday activities by themselves. This is called mild cognitive impairment (MCI).

It’s often not possible at this stage to say for sure that the person’s symptoms are being caused by Alzheimer’s disease, as there could be many other causes.
 
Eventually Alzheimer’s disease causes so much damage to the brain that the person develops dementia. Technically this type of dementia is called ‘Alzheimer’s disease dementia’. However, most people – including healthcare professionals – just call it ‘Alzheimer’s disease’.
 
For most people, Alzheimer’s disease starts in and around the part of the brain involved in memory. However, in some rarer types of dementia the disease starts in a different part of the brain and so causes a different set of symptoms. This is called ‘atypical Alzheimer’s’. For example, posterior cortical atrophy is caused by Alzheimer’s in the back of the brain and mostly causes problems with vision.  

What causes Alzheimer's disease

The causes of Alzheimer’s disease are very complex, but one key part is the build-up of two substances inside the brain called 'amyloid' and 'tau'. These proteins have been highlighted as a major contributors to what goes wrong inside the brain in this disease. 

When conditions in the brain aren’t right, these proteins clump up and form tiny structures called plaques and tangles. These make it harder for the brain to work properly. 

Over time the disease causes brain cells to die and certain parts of the brain to shrink. It also reduces the amount of important chemicals needed to send messages around the brain. Although amyloid plays an important role in Alzheimer's disease, it does not represent the whole picture.

There is currently no cure for Alzheimer’s disease. However, treatments may temporarily ease some symptoms or slow down their progression in some people. 

What are the main other types of dementia – and what causes them? 

• Vascular dementia: this the second most common type of dementia. It is caused by problems with the blood supply to parts of the brain.
• Lewy body dementia: Lewy bodies are tiny clumps of protein that build up in the brain. When this happens, it leads to Lewy body disease. There are two main types: 
  • Dementia with Lewy bodies:  When the first signs of Lewy body disease are symptoms of dementia, this is known as ‘dementia with Lewy bodies (DLB)’. 
  • Parkinson’s disease dementia: Lewy body disease can also cause Parkinson’s disease, which mostly involves problems with movement but can also lead to dementia several years later. If it does, this is known as Parkinson’s disease dementia. 
• Frontotemporal dementia: this is a less common type of dementia. It can be caused by several different types of disease but they all mostly affect the front or the sides of the brain, known as the frontal and temporal lobes.
• Mixed dementia: A diagnosis of mixed dementia is generally used when someone has a mixture of clinical symptoms from two or more different types of dementia – for example, if they have symptoms of both Alzheimer’s disease and dementia with Lewy bodies.  

How do I know what type of dementia I have? 

A diagnosis of dementia needs to be made by a healthcare professional who specialises in dementia, usually following a detailed assessment at a local memory service.  

When someone gets a diagnosis of dementia they should ideally be told by the doctor what type they have. This doesn’t always happen though. Sometimes it’s hard to tell what the cause of a person’s dementia is – particularly during the earlier stages.

It’s not always essential to know straight away what the cause of dementia is, but it can help to make better sense of the person’s symptoms and to get the right treatment.  

Does Alzheimer’s Society support people with dementia, as well as Alzheimer’s disease? 

We support anyone who has dementia. We can help guide people with mild cognitive impairment or who are worried about their memory. Find out how Alzheimer's Society can support you. 

We’re a vital source of support, giving help to everyone who needs it today, and hope for everyone in the future. 

This post was first published in July 2018 and most recently updated in November 2024.