Alzheimers appears to be a "shrinking" of the brain, and there is currently no cure. It appears that there is a buildup of plaque and damage to the neurons, etc., that reduces the size, and therefore, functions of the brain. In that regard, it may be somewhat related to the buildup of plaque in the arteries, which leads to things like stroke, and heart failure...but so far researchers have not been able to pinpoint the cause.
Most studies indicate that staying physically, and Mentally active is the best thing a person can do. There are many threads on the forum dedicated to various word games, etc., that can make a person think...and this may be a good thing, rather than just sitting around watching junk on TV all day. In many ways, the brain is like a muscle...If you Don't Use it, you Lose it.