It is not known exactly what causes this process to begin, although people with Alzheimer’s disease have been found to have abnormal amounts of protein (amyloid plaques), fibres (tau tangles) and a chemical called acetylcholine in the brain.
These reduce the effectiveness of healthy neurons (nerve cells that carry messages to and from the brain), gradually destroying them.
Over time, this damage spreads to several areas of the brain, such as the grey matter (responsible for processing thoughts) and the hippocampus (responsible for memory).
Although it is still unknown what triggers Alzheimer’s disease, several factors are known to increase your risk of developing the condition.
Age is the single most significant factor in the development of Alzheimer’s disease. The likelihood of developing the condition doubles every five years after you reach 65 years of age.
However, it is not just older people who are at risk of developing Alzheimer’s disease. Around 1 in 20 people with the condition are under 65. This is called early-onset Alzheimer’s disease and it can affect people from around 40 years of age.
The genes you inherit from your parents can contribute to your risk of developing Alzheimer’s disease, although the actual increase in risk is small if you have a close family member with the condition.
However, in a few families, Alzheimer’s disease is caused by the inheritance of a single gene, and the risks of the condition being passed on are much higher.
If several of your family members have developed dementia over the generations, it may be appropriate to seek genetic counselling for information and advice about your chances of developing Alzheimer’s disease when you are older.
The Alzheimer’s Society website has more information about genetics and dementia.
People with Down’s syndrome are at a higher risk of developing Alzheimer’s disease.
This is because the genetic fault that causes Down’s syndrome can also cause amyloid plaques to build up in the brain over time, which can lead to Alzheimer’s disease in some people.
Whiplash and head injuries
People who have had a severe head injury or severe whiplash (a neck injury caused by a sudden movement of the head) have been found to be at higher risk of developing Alzheimer’s disease.
Research shows that several lifestyle factors and conditions associated with cardiovascular disease can increase the risk of Alzheimer’s disease.
- high blood pressure
- high cholesterol
You can help reduce your risk by stopping smoking if you smoke, eating a healthy, balanced diet, and having regular health checks as you get older. It is also important to keep as active as possible, both mentally and physically, to help reduce the risk of Alzheimer’s disease.
While scientists know Alzheimer’s disease involves progressive brain cell failure, the reason cells fail isn’t clear. Like other chronic conditions, experts believe that Alzheimer’s develops as a complex result of multiple factors rather than any one overriding cause.
Both age and genetics have been identified as risk factors, but many questions still remain. The discovery of additional risk factors will deepen our understanding of why Alzheimer’s develops in some people and not others.
- Age and Alzheimer’s
- Family history and Alzheimer’s
- Genetics and Alzheimer’s
- Related information
- Age and Alzheimer’s
Although Alzheimer’s is not a normal part of growing older, the greatest risk factor for the disease is increasing age. After age 65, the risk of Alzheimer’s doubles every five years. After age 85, the risk reaches nearly 50 percent.
Family history and Alzheimer’s
Another Alzheimer’s risk factor is family history. Research has shown that those who have a parent, brother, sister or child with Alzheimer’s are more likely to develop the disease. The risk increases if more than one family member has the illness. When diseases tend to run in families, either heredity (genetics) or environmental factors or both may play a role.
Genetics and Alzheimer’s
There are two categories of genes that influence whether a person develops a disease: (1) risk genes and (2) deterministic genes. Researchers have identified Alzheimer’s genes in both categories.
Genetics in Alzheimer’s (approx 14 min.)
Risk genes increase the likelihood of developing a disease, but do not guarantee it will happen. Researchers have found several genes that increase the risk of Alzheimer’s. APOE-e4 is the first risk gene identified, and remains the gene with strongest impact on risk. APOE-e4 is one of three common forms of the APOE gene; the others are APOE-e2 and APOE-e3.
Everyone inherits a copy of some form of APOE from each parent. Those who inherit one copy of APOE-e4 have an increased risk of developing Alzheimer’s. Those who inherit two copies have an even higher risk, but not a certainty.
In addition to raising risk, APOE-e4 may tend to make symptoms appear at a younger age than usual. Scientists estimate that APOE-e4 is implicated in about 20 percent to 25 percent of Alzheimer’s cases.