Although scientists are unsure of the initial cause of Alzheimer's disease, it is known that the symptoms of Alzheimer's disease are caused by the disconnection and death of neurons in the brain. Based on what scientists understand about Alzheimer's disease, the following have been established as risk factors for the disease:

• Age. By far the greatest risk factor for developing Alzheimer's disease is age. The number of people with Alzheimer's disease doubles every five years after the age of 65, according to the National Institute of Neurological Disorders and Stroke (NINDS).
  
  
• Family history. People who have a sibling or parent with Alzheimer's disease are more likely to develop the disease themselves. This risk is greater if more than one member of the family has been diagnosed with Alzheimer's disease. Although the phenomenon is still being studied, it is thought to be related to a slight variation in the genes of certain people that makes them especially susceptible to the disease.
  
  
• Head injury. There is strong evidence that suggests that people who sustain serious head injury are more likely to develop Alzheimer's disease later in life. However, this link has not been firmly substantiated by medical research and is more commonly linked to other forms of dementia.
  
  
• Lifestyle factors. Although this is somewhat controversial, a number of lifestyle factors might play a role in the development of Alzheimer's. These include lack of exercise, lack of access to a social network, and lack of mentally stimulating activities. For example, numerous studies have shown that people with advanced degrees are less likely to develop Alzheimer's, possibly due to increased brain elasticity. In addition, there may be a link between obesity and the metabolic syndrome and Alzheimer's disease.
  
  
• Environmental factors. There have been some reports linking aluminum to an increased risk of developing Alzheimer's disease. Aluminum is a common element that is found naturally in the environment as well as in various household products. Although toxic levels of exposure to aluminum is known to cause some neurological symptoms, the role of aluminum in the development of Alzheimer's disease is not fully understood. Many experts believe that the risks associated with normal aluminum exposure are low.