Researchers do not yet know the cause of Alzheimer's disease. The most important risk factor appears to be age. According to the National Institute on Aging, the number of people with Alzheimer's doubles every 5 years after the age of 65.
Another risk factor or cause of Alzheimer's appears to be family history. A family form, or familial Alzheimer's disease, is a rare form of Alzheimer's that usually occurs early--between the ages of 30 and 60--and can be inherited.
The more common form of Alzheimer's, which occurs later in life, does not have an obvious link to family history. However, one risk factor for this type of Alzheimers disease is a protein or gene called the apolipoprotein E or the apoE gene.
ApoE helps carry cholesterol in the blood. The apoE gene has three forms. One seems to protect a person from Alzheimer's. One appears to be neutral and neither protects nor assists in the development of the disease. And finally, the last form appears to make a person more likely to develop Alzheimer's. Undoubtedly, there are other genes that increase the risk of AD that are yet to be discovered. Weight, environment, level of education, and gender are all associated with Alzheimer's. With the exception of gender (more women have Alzheimer's than men); these factors may slow down or speed up the course of the disease, rather than contribute to the cause of Alzheimer's. Recently, a study of women in Sweden revealed that obesity in women is associated with a decrease in brain matter-whether or not this will be associated with Alzheimer's remains to be seen, but it is an example of how overall health can affect the course of the disease. In another study, researchers discovered that the more formal education a person has the better his or her memory and learning ability will be, even in the presence of Alzheimer's disease. In other words, formal education preserved memory and function, even among those persons with Alzheimer's.