Besides the critical function of allowing our cells to process glucose correctly, malic acid also binds to excess aluminum and pulls it out of the body, helping prevent aluminum toxicity (and, if you believe in the aluminum/Alz. connection, may prevent Alz.). Here's this clip:

"The Aluminum - Magnesium Link

Research have suggested that aluminum may be more likely to accumulate in the brains of persons whose diets are magnesium-deficient -- which, unfortunately, includes 90% of Americans! Several studies have shown that animals fed diets low in magnesium accumulate high concentrations of aluminum in the Central Nervous System. One of magnesium's many functions is to activate the enzyme tubulin involved in the maintenance of nerve tissue cells. It has been suggested that when there is not enough Magnesium in the body to plug into the appropriate receptor site on the tubulin enzyme, aluminum takes its place instead. This leads to the inactivation of tubulin and, consequently, inadequate nerve function. Malic acid can pull aluminum away from this enzyme, making a place for magnesium. This may be a protection against Alzheimer's disease. Malic Acid is found abundantly in fruits such as apples. Malic Acid is also produced in the human body. It is a metabolite of the Krebs cycle the set of biochemical reactions used to produce 90% of all energy in the cells of the body. Malic Acid readily crosses the Blood-Brain-Barrier and has been shown to bind to aluminum. It functions in the body by drawing aluminum away from the tubulin enzyme, so that Magnesium can plug into the receptor sites instead. Malic Acid's unique ability to bind with aluminum means it can be flushed out of the body, preventing unwanted build-up."

From: http://www.angelfire.com/az/sthursto..._toxicity.html

Flouridated water, by the way, contributes to our aluminum load:

"Treated municipal water - Many municipal water supplies are treated with alum (aluminum sulfate) to get rid of murkiness. At least seven separate studies have shown that people drinking water high in alum are more likely to develop Alzheimer's than people drinking water low in alum. The worst part is that alum can combine with flouride in the blood to form aluminum fluoride. About 300,000,000 pounds of sodium fluoride, an industrial waste from aluminum refiners, is added to our water supply each year. (see Fluoridated Water)

Aluminum researcher Elizabeth Jeffery has found evidence that flouride interferes with the body's ability to get rid of aluminum. She says, "My research indicates that flouride readily combines with aluminum in the blood, and that aluminum flouride, once formed is very poorly excreted in the urine." She believes that the aluminum fluoride then becomes concentrated in the bones (where flourine replaces calcium) and continues to slowly release and recycle through the body over time. Albert Burgstahler, a professor of biochemistry at the University of Kansas, has found that aluminum flouride can pass unusually well through biological barriers, notably the blood-brain barrier, and accululate in the brain."

From the same website source as above.

Aluminum is everywhere, in our water, in our foods, deodorant, shampoos, toothpastes, medicines, even fillings. Like most things, we have to have a small amount of aluminum to survive, but in our world of today it looks like we are being inundated, and our bodies cannot process the stuff out fast enough.

My take away from this is that we are all probably getting way more aluminum than we need, and to offset that, eat foods rich in magnesium and/or supplement, and be sure you get enough malic acid, either from apples (or other food source, but apples appear to be one of the highest food sources) or a supplement.