Alzheimer's disease: Causes and prevention
Alzheimer's disease is a form of dementia affecting around 500,000 people in the UK, according to the NHS. A progressive loss of cells in the brain gradually affects memory, behaviour and other brain functions.
Although doctors know what happens to the brain with Alzheimer's disease, the reason the condition develops and affects some people and not others is less clear.
Some causes and risk factors have been established, and there are some lifestyle changes a person can make to help reduce their risk of developing Alzheimer's disease.
What causes Alzheimer's disease?
People are more likely to develop Alzheimer's disease as they grow older, but the disease is not a natural result of ageing. It is an abnormal condition the causes of which continue to be investigated.
The gradual loss of brain function that characterises Alzheimer's disease seems to be due to two main forms of nerve damage:
- Nerve cells develop tangles (neurofibrillary tangles)
- Protein deposits known as plaques build up in the brain.
Researchers are not yet sure why or how these processes occur, but some of the most promising recent research points to a normally occurring blood protein called ApoE (for apolipoprotein E), which is required for the transport of fatty substances in the body.
As with all proteins, the form of ApoE that each person has in their body is genetically determined and several different types have been identified - some of them apparently associated with a higher risk of Alzheimer's. It may be that certain forms of ApoE lead to the nerve damage.
Another possibility is that the protein, perhaps working in combination with other substances, is involved in the formation of the plaques. Whether or not ApoE partly causes Alzheimer's disease, genes almost certainly play a role in the disease and a person with a parent who had Alzheimer's disease is at higher risk.
Other causes have been proposed. One theory suggests that ingesting tiny particles of aluminium - from pots and pans, for example - may lead to Alzheimer's. Another proposes a link between plaque formation and free radicals - unstable, free-ranging molecules that can produce destructive chemical reactions. Both theories are controversial and unproven. Indeed, many researchers now consider the link between Alzheimer's and aluminium extremely questionable.
Another controversy centres on zinc, with the connection between zinc and Alzheimer's remaining unclear. It is thought that at low levels zinc may be protective but at higher doses it may be harmful, promoting the development of plaques that are associated with Alzheimer’s, although scientists remain unsure whether plaques cause Alzheimer's or are themselves a result of the disease. If the latter, zinc's ability to form plaques might be unrelated to what causes Alzheimer's disease in the first place.
There is some evidence that people with high blood pressure and high cholesterol have an increased chance of developing Alzheimer's. In a minority of cases, trauma may be a contributing factor. The more severe the head injury, the greater the risk of Alzheimer's dementia later in life.
While many of these theories are still being studied, it is clear that the biggest risk factors associated with developing Alzheimer's disease are increasing age and family history.