Dementia guide

Causes of dementia

Dementia is caused by damage in the brain. The most common causes of dementia are called neurodegenerative diseases, and include Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies. With these diseases, the brain cells degenerate and die more quickly than is part of the normal ageing process. This leads to a decline in a person's mental and, sometimes, physical abilities. The gradual changes and damage to brain cells are caused by a build-up of abnormal proteins in the brain.

These abnormal proteins are different in each type of neurodegenerative dementia. In most cases, dementia is not inherited directly from family members. However, a small number of cases of Alzheimer's disease and frontotemporal dementia can run in families.

Vascular dementia is caused when the brain's blood supply is interrupted. If the blood supply is restricted or stopped, brain cells begin to die, resulting in brain damage.

The causes of the different types of dementia are listed below.

Causes of Alzheimer's disease

Alzheimer's disease is the most common form of dementia. In Alzheimer's disease, the loss of brain cells leads to the brain shrinking. The medical name for this is atrophy.

An area of the brain known as the cerebral cortex is particularly affected by atrophy. The cerebral cortex is the layer of grey matter covering the brain. Grey matter is responsible for processing thoughts and many of the complex functions of our brains, such as storing and retrieving memories, calculation, spelling, planning and organising.

Clumps of protein, known as "plaques" and "tangles", progressively form in the brain. The plaques and tangles are thought to be responsible for the increasing loss of brain cells. Connections between brain cells are lost and there are less neurotransmitter chemicals available to carry messages from one brain cell to another. They also affect the chemicals that carry messages between brain cells.

Causes of vascular dementia

Vascular dementia is caused when the brain's blood supply is interrupted.

Like all organs, the brain needs a constant supply of oxygen and nutrients from the blood to work properly. If the supply of blood is restricted or stopped, the brain cells will begin to die, resulting in brain damage.

If the blood vessels inside the brain narrow and harden, the brain's blood supply can gradually become interrupted. The blood vessels usually narrow and become hard when fatty deposits build up on the blood vessel walls, restricting the flow of blood. This is called atherosclerosis, and is more common in people who have high blood pressure, type 1 diabetes and those who smoke.

Atherosclerosis in the smaller blood vessels in the brain will also cause them to clog up gradually, depriving the brain of blood. This is known as small vessel disease. 

If the brain's blood supply is interrupted rapidly during a stroke, this can also damage brain cells. 

Not everyone who has had a stroke will go on to develop vascular dementia. However, if you have had a stroke or you have been diagnosed with small vessel disease, you may have an increased risk of developing vascular dementia.

Read more about vascular dementia.

Causes of dementia with Lewy bodies

Lewy bodies are small, circular lumps of protein that develop inside brain cells. It is not known what causes them. It is also unclear how they damage the brain and cause dementia.

One theory is that Lewy bodies interfere with the effects of two of the messenger chemicals in the brain – dopamine and acetylcholine. These messenger chemicals, which send information from one brain cell to another, are called neurotransmitters.

Dopamine and acetylcholine are thought to play an important role in regulating brain functions, such as memory, learning, mood and attention.

Dementia with Lewy bodies is closely related to Parkinson's disease. This is a condition where part of the brain becomes more and more damaged over a number of years, leading to physical symptoms, such as involuntary shaking (tremor), muscle stiffness and slowness of movement. A person with dementia with Lewy bodies may also develop these symptoms.

Read more about dementia with Lewy bodies.

Causes of frontotemporal dementia

Frontotemporal dementia is caused by damage and shrinking in two areas of the brain. The areas of the brain affected are called the temporal lobe and the frontal lobe. This type of dementia is one of the more common types seen in people who are under 65 years of age.

In an estimated 20% of cases, people who develop frontotemporal dementia have inherited a genetic mutation (an altered gene) from their parents.

Motor neurone disease is also sometimes associated with frontotemporal dementia. It is a rare condition that progressively damages the nervous system, causing the muscles to waste away.

Read more about frontotemporal dementia.

Less common causes of dementia

Other causes of dementia or dementia-like conditions may be treatable or non-progressive (meaning that they do not continue to get worse with time). These can include:

There are also rarer causes of neurodegenerative dementia, including:

Page last reviewed: 19/06/2013

Next review due: 19/06/2015

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The 1 comments posted are personal views. Any information they give has not been checked and may not be accurate.

frank adey said on 12 December 2013

There does seem to be many more cases of Dementia and Alzheimers developing...are there any clues as to what may be triggering this.
As it not only effects old, but all ages. Is there something in our habits since 2000 to 2013 that may be cortributing to this developement?
What research is being done to try to find a link or cause?

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