Another Alzheimer's theory is that it's sugar/carbohydrate related. Lots of very good evidence for it, look up "sugar and Alzheimer's" for some info. It's not getting much press (for obvious reasons) but here's a article.

https://www.theatlantic.com/health/archive/2018/01/the-startling-link-between-sugar-and-alzheimers/551528/