Dementia is caused by gradual changes and damage in the brain. The most common causes of dementia include diseases in which the brain cells degenerate and die more quickly than they would as part of the normal ageing process. The changes usually happen because of a build-up of abnormal proteins in the brain.
This damage leads to a decline in a person's mental and, sometimes, physical abilities.
The abnormal proteins are different in each type of these kinds of dementia. In most cases, dementia is not inherited directly from family members. However, frontotemporal dementia can sometimes run in families.
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, leading to 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 bloodflow. 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 the causes of vascular dementia.
Causes of Alzheimer's disease
Alzheimer's disease is the most common form of dementia. In Alzheimer's, the loss of brain cells leads to the brain shrinking.
Part of the brain known as the cerebral cortex is particularly affected by this shrinkage. 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", gradually 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 less neurotransmitter chemicals are available to carry messages from one brain cell to another. The plaques and tangles also affect the chemicals that carry messages between brain cells.
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.
It's possible that Lewy bodies interfere with the effects of two of the messenger chemicals in the brain called 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 slow 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 from their parents.
Motor neurone disease is sometimes associated with frontotemporal dementia. It is a rare condition that damages the nervous system over time, 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 they do not continue to get worse with time). These can include:
There are also rarer causes of neurodegenerative dementia, including:
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