Alzheimer's disease: Causes and risk factors

We do not understand the exact cause of Alzheimer's disease, but it probably results from a complex set of factors.

What happens in the brain?

There are certain abnormalities found in the brains of people with Alzheimer's, but experts don't know whether these cause the disease or are a result of the disease.

Neurofibrillary tangles are twisted structures formed from part of the nerve.

Beta amyloid is a sticky substance that clumps to form structures called plaques. Plaques and tangles damage the healthy brain cells that surround them, causing the brain to waste away and shrink.

Another characteristic of Alzheimer's disease is that brain cells produce reduced amounts of chemicals, known as neurotransmitters that are required for communication between nerves. These chemicals include acetylcholine, serotonin, and norepinephrine.

Risk factors

Factors that may increase the risk of Alzheimer's disease include:

• Age. The risk of developing Alzheimer's disease increases with age. In the UK, one person out of 20 aged 65 and over has the disease. People over the age of 80 are thought to have a one in five chance of developing the condition.
• Gender. Alzheimer's disease affects women more frequently than men.
• Family history. About one in four cases are familial, meaning that more than one person is affected in the same family. First-degree relatives of a patient with Alzheimer’s disease have about a 2.5-fold increased risk of developing the condition themselves. In addition, a less common type of Alzheimer’s disease that starts before age 65 may be directly inherited.
• Down’s syndrome. People with Down’s syndrome often develop Alzheimer's disease in their 30s and 40s, although the exact reason is not known.
• Head injury. Some studies have shown a link between Alzheimer's disease and a significant head injury in the past.
• Environmental toxins. Some researchers suspect that increased exposure to certain substances, such as aluminium, may make a person more susceptible to Alzheimer's disease.
• Low education level. Although the reason is not clearly understood, some studies have shown that low education levels can be related to an increased risk of Alzheimer's disease.
• Other factors. Research suggests that high cholesterol levels and high blood pressure (factors linked to heart disease and strokes) may also increase the risk of developing Alzheimer's.