I have read studies where that theory is disputed and I have seen studies where that theory is proved.  The bottom line is that there is no firm study that prove the link. If you are making this perfect sweet potato every day, then maybe using an aluminum foil might be problematic.  Using aluminum foil once in a while is ok. Truth is, Alzheimers is very complicated and there is no one source. I like using foil because it circulates the heat evenly.  At the end of the day, you have to do what you think is right for you.  No judgments here!