Causes of dementia
Dementia is a term used to describe the symptoms that occur when there's a decline in brain function.
Dementia is not a single disease. There are different diseases that can cause dementia. Many of these diseases are associated with an abnormal build-up of proteins in the brain.
This build-up causes nerve cells to function less well and ultimately die. As the nerve cells die, different areas of the brain shrink.
Causes of Alzheimer's disease
Alzheimer's disease is the most common type of dementia.
Alzheimer's disease is thought to be caused by the abnormal build-up of 2 proteins called amyloid and tau.
Deposits of amyloid, called plaques, build up around brain cells. Deposits of tau form "tangles" within brain cells.
Researchers do not fully understand how amyloid and tau are involved in the loss of brain cells, but research into this is continuing.
As brain cells become affected in Alzheimer's, there's also a decrease in chemical messengers (called neurotransmitters) involved in sending messages, or signals, between brain cells.
Levels of 1 neurotransmitter, acetylcholine, are particularly low in the brains of people with Alzheimer's disease.
Medicines like donepezil increase levels of acetylcholine, and improve brain function and symptoms.
These treatments are not a cure for Alzheimer's disease, but they do help improve symptoms.
Read more about treatments for dementia.
The symptoms that people develop depend on the areas of the brain that have been damaged by the disease.
The hippocampus is often affected early on in Alzheimer's disease. This area of the brain is responsible for laying down new memories. That's why memory problems are one of the earliest symptoms in Alzheimer's.
Unusual forms of Alzheimer's disease can start with problems with vision or with language.
Read more about Alzheimer's disease.
Causes of vascular dementia
Vascular dementia is caused by reduced blood flow to the brain, which damages and eventually kills brain cells.
This can happen as a result of:
- narrowing and blockage of the small blood vessels inside the brain
- a single stroke, where the blood supply to part of the brain is suddenly cut off
- lots of "mini strokes" that cause tiny but widespread damage to the brain
Not everyone who has a stroke will go on to develop vascular dementia.
Read more about vascular dementia.
Because both vascular dementia and Alzheimer's disease are common (especially in older people) they may be present together.
This is often called mixed dementia because a mix of these 2 conditions is thought to be the cause of the dementia.
It can be difficult to know how much each cause is contributing to a person's problems.
Causes of dementia with Lewy bodies
Lewy bodies are tiny clumps of a protein called alpha-synuclein that can develop inside brain cells.
These clumps damage the way the cells work and communicate with each other, and the brain cells eventually die.
Dementia with Lewy bodies is closely related to Parkinson's disease and often has some of the same symptoms, including difficulty with movement and a higher risk of falls.
Read more about dementia with Lewy bodies.
Causes of frontotemporal dementia
This is an important cause of dementia in younger people. It's most often diagnosed between the ages of 45 and 65.
It's caused by an abnormal clumping of proteins, including tau, in the frontal and temporal lobes at the front and sides of the brain.
The clumping of these proteins damages nerve cells in the frontal and temporal lobes, causing brain cells to die. This leads to shrinking of these areas of the brain.
Frontotemporal dementia is more likely to run in families than other, more common causes of dementia.
Read more about frontotemporal dementia.
Rarer causes of dementia
There are many rarer diseases and conditions that can lead to dementia, or dementia-like symptoms.
These conditions account for only 5% of dementia cases in the UK.
Mild cognitive impairment
Mild cognitive impairment (MCI) is not a cause of dementia.
it’s a term used to describe minor memory and thinking problems, such as:
- memory loss
- difficulty concentrating
- problems with planning and reasoning
These symptoms are not severe enough to cause problems in everyday life.
If the underlying illness is treated or managed, symptoms of MCI often disappear and cause no further problems.
But in some cases, people with MCI are at increased risk of going on to develop dementia, which is usually caused by Alzheimer's disease.
Read more about how to prevent dementia.
Take part in dementia research
There are many dementia research projects and clinical trials going on around the world, many of which are based in the UK.
If you have a dementia diagnosis or are worried about memory problems, you can help scientists understand more about it, and develop possible treatments, by taking part in research.
Carers can also take part, as there are studies into the best ways to care for someone with a dementia diagnosis.
Video: early onset dementia
In this video, an expert explains the value of early diagnosis and planning for the future.
Media review due: 1 July 2024
Page last reviewed: 11 January 2021
Next review due: 11 January 2024