Understanding Alzheimer's Disease -- the Basics
What Causes Alzheimer's Disease? continued...
As with all proteins, the form of ApoE that people have in their bodies is genetically determined, and several different types have been identified -- some of them apparently associated with a higher risk of Alzheimer's. It may be that certain forms of ApoE lead to the nerve damage.
Another possibility is that the protein, perhaps working in combination with other substances, is involved in the formation of the plaques. Whether or not ApoE partly causes Alzheimer's disease, genes almost certainly play a role in the disease, and a person with a parent who had Alzheimer's disease is at higher risk.
Other causes have been proposed: One theory suggests that ingesting tiny particles of aluminum -- from cookware, for example -- may lead to Alzheimer's. Another proposes a link between plaque formation and free radicals -- unstable, free-ranging molecules that can produce destructive chemical reactions. Both theories are controversial and unproven. Indeed, many researchers now consider the link between Alzheimer's and aluminum extremely questionable.
Another controversy centers on zinc -- both excess zinc and zinc deficiency -- but the connection to Alzheimer's remains unclear. It is thought that at low levels zinc may be protective, but at higher doses it may be harmful. Yet, scientists remain unsure whether plaques cause Alzheimer's or are themselves a result of the disease. If the latter, zinc's ability to form plaques might be unrelated to what causes Alzheimer's disease in the first place.
There is some evidence that people with high blood pressure and high cholesterol have an increased chance of developing Alzheimer's. In a minority of cases, head trauma may be a contributing factor (the more severe the head injury, the greater the risk of Alzheimer's dementia later in life).
While many of these theories are still being studied, it is clear that the biggest risk factors associated with developing Alzheimer's disease are increasing age and family history.