Alzheimer's Disease: Causes and Risk Factors
In-depth information on the causes and risk factors of Alzheimer's Disease.
The causes of Alzheimer's disesase are not entirely known but are thought to include genetics and environmental factors. New research indicates that free radicals (highly reactive molecules that can cause oxidation, or damage to cells) may play a role in the development of AD.
A gene for the protein epsilon apolipoprotein (Apo E)—especially Apo E3 and Apo E4 varieties—is thought to accelerate the formation of abnormal deposits (called plaques) in the brain and increase the risk for AD. Reports indicate that between 50% and 90% of those with the Apo E4 gene develop AD. However, even people without inherited genes for the disease can get AD.
Scientists also believe the environment may play a part in AD because people in different regions of the world have widely varying risks of developing the disease. For example, people living in Japan and West Africa have much less risk for AD than Japanese and Africans living in the United States.
People with Alzheimer's disease have abnormal deposits, or plaques, in their brain tissue. These plaques contain beta amyloid, a protein that releases free radicals, or highly reactive molecules that can cause damage to cells through a process called oxidation. These free radicals are believed to lower levels of acetylcholine (a brain chemical that helps transmit impulses in the nervous system) and damage brain tissue, bringing on the symptoms of AD.
Although not confirmed by scientific studies, other factors that have been speculated to contribute to the development of AD include infections (such as herpesvirus type 1), exposure to metal ions (such as aluminum, mercury, zinc, copper, and iron), or prolonged exposure to electromagnetic fields.
The causes and risk factors contributing to the development of Alzheimer's disease are not entirely clear. The following all appear to have an association with AD to varying degrees.
- Family history of Alzheimer's disease
- Older age—20% to 40% of people with AD are older than 85
- Female gender—while women tend to develop AD more than men, this may be related to the tendency for women to live longer
- Americans are more likely to get AD than Asians or Native Americans
- Long-term high blood pressure
- History of head trauma—one or more serious blows to the head may put a person at an increased risk
- Down Syndrome
- Elevated levels of homocysteine (a body chemical that contributes to chronic illnesses such as heart disease, depression, and AD)
- Aluminum or mercury poisoning
- Prolonged exposure to electromagnetic fields
- Consuming a low-fat, low-calorie diet may reduce the risk for Alzheimer's.
- Higher intake of fatty, cold-water fish (such as tuna, salmon, and mackerel) has been associated with a lower risk of dementia. This may be due to the high level of omega-3 fatty acids found in such fish. Eating fish at least two to three times per week provides a healthy amount of omega-3 fatty acids.
- Reducing intake of linoleic acid (found in margarine, butter, and dairy products) may prevent cognitive decline.
- Antioxidants, such as vitamins A, E, and C (found in darkly colored fruits and vegetables) may help prevent damage caused by free radicals.
- Maintaining normal blood pressure levels may reduce the risk for AD.
- Hormone-replacement therapy in postmenopausal women may decrease production of chemicals that cause AD, stimulate growth of brain cells, and improve blood flow in the brain. However, the role of hormones in the prevention of AD is still controversial.
- Some studies suggest that certain medications may prevent AD, including "statin" drugs (such as pravastatin or lovastatin, used to lower cholesterol) and nonsteroidal anti-inflammatories (NSAIDs), with the exception of aspirin. More research is necessary, however, to determine how effective these medications are in reducing the risk of the disease.
- Keeping mentally and socially active may help delay the onset or slow the progression of AD.
Last Updated: 25 February 2016
Reviewed by Harry Croft, MD