Does reading, and posting, in endless forum threads help your brain too ??
Does chess prevent alzheimer's disease?

I have an old man in my Spanish class who is learning so that he can delay the onset of Alzheimers, apparently his physician or whatever told him it would help to learn another language.
If that's true than I can definitely see playing/learning chess being of similar benefit, as even reading/interpretting notation itself is like learning a new language!
Learning a new language helps a lot. Learning to use computers, or a smartphone, also helps tremendously.
Chess is strongest when it is played for hours. For instance, I had a very important exam last july, the kind of exam that can get you the job of your life. It took an average of 7 hours to finish the exam. We were allowed to stop for 5 minutes. Most didn't know how to efficiently feed the brain in only 5 minutes. It took me 1 minute. I used the same food I would use in a tournament. At the end of the exam people were exhausted, I was fine, Chess is more taxing,I said to myself.
I noticed the difference because 4 years ago when I took the same exam I was brain dead after 4 hours. I've been playing chess for 3 years now.
Oh! I passed the exam ;)

Pulp; he had a picture of me. He just kept saying, "I have to pass this, I don't want to end up like THAT guy".

"There's been more than 1 million professional chess players only in the 20 century. So, Chess has been tested on over 1 million subjects and none showed symptoms of the disease."
Frankly, I find this extremely difficult to believe.
First off - how are they defining "professional chess player" here? Is it people who have been able to make a living just from playing chess? Are they counting anyone who's played in a tournament for a little prize money? How do they arrive at such an outlandish figure?
Second - what is their method for ascertaining that not a single one has had Alzheimer's? Has there been someone who's followed these supposed 1,000,000 players around their entire lives over the course of the previous 100 years, keeping tabs on each person and their medical history to make note of any occourance of Alzheimer's? Again, how do they arrive at such an extraordinary claim?
I realize that folks like to elevate their hobbies and pastimes, but in the course of such elevation one should probably refrain from making claims that just don't sound believable to any kind of rational scrutiny.
Now I'll try to make my 78-year old grandfather learn chess. But apparently he is in middle stage Alzheimer so I guess it may only slow it down rather than stopping. ;)