Most cases are caused by Alzheimer's disease, vascular dementia, or dementia with Lewy bodies (DLB). All these types of dementia cause similar symptoms but some features may point to a particular cause. However, it may not be possible to say what is causing the dementia in every case.
This is the most common type of dementia, causing at least half of all cases, possibly up to three quarters. It is named after the doctor who first described it. In Alzheimer's disease the brain shrinks (atrophies) and the numbers of nerve fibres in the brain gradually reduce. The amount of some brain chemicals (neurotransmitters) is also reduced - in particular, one called acetylcholine. These chemicals help to send messages between brain cells. Tiny deposits called plaques also form throughout the brain. It is not known why these changes in the brain occur, or exactly how they cause dementia. Alzheimer's disease gradually progresses (worsens) over time as the brain becomes more and more affected.
Blood vessel dementia (vascular dementia)
This causes about a fifth of all cases of dementia. It is due to problems with the small blood vessels in your brain. The most common type is called multi-infarct dementia. In effect, this is like having many tiny strokes, that otherwise go unrecognised, throughout the thinking part of the brain. A stroke occurs when a blood vessel blocks and stops the blood getting past. So, the section of brain supplied by that blood vessel is damaged or dies (an infarct occurs). After each infarct, some more brain tissue is damaged. So, a person's mental ability gradually declines. Vascular dementia can also sometimes happen after a more major stroke.
The risk of developing vascular dementia is increased by the same things that increase the risk of stroke. For example: high blood pressure, smoking, a high cholesterol level, lack of exercise, etc. See separate leaflet called Preventing Cardiovascular Diseases for more details. However, it is now thought that some of these vascular risk factors may also be involved in the development of Alzheimer's disease and other types of dementia as well.
Lewy body dementia/dementia with Lewy bodies (DLB)
This causes 10 to 15 in every 100 cases of dementia. Lewy bodies are tiny abnormal protein deposits that develop in nerve cells in the brain of people with this condition. It is not clear why the Lewy bodies develop but they interfere with the normal working of the brain.
If Lewy bodies develop in a part of the brain called the brain stem, as well as symptoms of dementia, someone may also develop symptoms similar to Parkinson's disease. For example, stiffness, slowness of movement and a shuffling walk with difficulty in starting, stopping, and in turning easily.
Some people can have a degree of two different types of dementia at the same time. For example, both Alzheimer's disease and vascular dementia, or both Alzheimer's disease and DLB. This is known as mixed dementia. However, in most cases of mixed dementia, there is usually one of the causes for dementia that is thought to be the main (predominant) cause. In this situation, treatment is aimed at the predominant cause of dementia.
Other causes of dementia
There are over 60 diseases which can cause dementia. Many are rare and, in many, the dementia is just part of other problems and symptoms. In most cases the dementia cannot be prevented or reversed. However, in some disorders the dementia can be prevented, or stopped from getting worse if treated. For example, some cases of dementia are caused by alcohol abuse, infections such as syphilis, or some vitamin deficiencies, all of which can be treated.
Who gets dementia?
Dementia is a common problem. According to figures provided by the Alzheimer's Society, there are currently 835,000 people with dementia in the UK. It is estimated that there will be over two million by 2050. The older you are the higher chance there is of getting dementia. Between the ages of 65 and 74, 1-3 people in 100 will have dementia. By the age of 95, 41 people in 100 will have it. However, dementia is not a normal part of ageing. It is different to the age-associated memory impairment that is common in older people. Rarely, dementia affects younger people. Dementia is said to be early-onset (or young-onset) if it comes on before the age of 65. There are some groups of people who are known to have a higher risk of developing dementia. These include people with:
- Down's syndrome or other learning disabilities. People with Down's syndrome are more likely to develop Alzheimer's disease.
- Parkinson's disease. As many as half of people with Parkinson's disease may develop dementia.
- Risk factors for cardiovascular disease (angina, heart attack, stroke and peripheral arterial disease). The risk factors for cardiovascular disease (high blood pressure, smoking, a high cholesterol level, lack of exercise, etc) are risk factors for all types of dementia, not just blood vessel dementia (vascular dementia).
- A past history of a stroke.
- A history of drinking excess alcohol.
- A family history of dementia. There is a small extra risk of getting dementia if you have a mother, father or sibling with dementia. Dementia also seems to run in some families so there may be some genetic factors that can make someone more likely to develop dementia. We do know that a few of the more rare causes of dementia can be inherited (can be passed on through genes in your family).
- Severe psychiatric problems such as schizophrenia or severe depression. It is not clear why this is the case.
- A past history of a head injury.
- Lower intelligence. Some studies have shown that people with a lower IQ and also people who do not have very high educational achievement are more likely to develop dementia.
- A limited social support network.
- Low physical activity levels. A lack of physical activity can increase your risk of dementia. See separate leaflet called Physical Activity for Health for more details.
Further reading and references
Dementia; NICE CKS, August 2016 (UK access only)
Dementia Fact Sheet; World Health Organization (WHO), April 2016
Donepezil, galantamine, rivastigmine and memantine for the treatment of Alzheimer's disease; NICE Technology Appraisal Guidance, March 2011
Guidelines for the diagnosis and management of Alzheimer's disease; European Federation of Neurological Societies (2010)
Robinson L, Tang E, Taylor JP; Dementia: timely diagnosis and early intervention. BMJ. 2015 Jun 16350:h3029. doi: 10.1136/bmj.h3029.
Dementia: Supporting people with dementia and their carers in health and social care; NICE Clinical Guideline (November 2006, last updated September 2016)
Dementia, disability and frailty in later life – mid-life approaches to delay or prevent onset; NICE Guidelines (October 2015)
Health matters: midlife approaches to reduce dementia risk; Public Health England Guidance, March 2016
Laver K, Dyer S, Whitehead C, et al; Interventions to delay functional decline in people with dementia: a systematic review of systematic reviews. BMJ Open. 2016 Apr 276(4):e010767. doi: 10.1136/bmjopen-2015-010767.
Howard R, McShane R, Lindesay J, et al; Donepezil and memantine for moderate-to-severe Alzheimer's disease. N Engl J Med. 2012 Mar 8366(10):893-903. doi: 10.1056/NEJMoa1106668.
Brechin D et al; Alternatives to antipsychotic medication: Psychological approaches in managing psychological and behavioural distress in people with dementia, The British Psychological Society, March 2013
Living with dementia - Planning ahead; Alzheimer's Society
Dementia; NICE Quality Standard, June 2010
Dementia: independence and wellbeing; NICE Quality Standard, April 2013
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