Possibly related: there's some interesting work on the increased risk of Alzheimer's for carriers of an ApoE4 genotype that seems to block perfusion of DHA: https://pubmed.ncbi.nlm.nih.gov/27358067/

Dr. Rhonda Patrick has an interesting hypothesis around phospholipid-bound DHA potentially being a remediation:

https://faseb.onlinelibrary.wiley.com/doi/10.1096/fj.201801412R (TLDR: eat fish eggs)

That ApoE4 genotype also seems to change brain glucose and ketone metabolism: https://www.jneurosci.org/content/38/30/6665.

Unrelated: I find ApoE4 interesting as it's a perfect example of antagonistic pleiotropy (something that's adaptive when young( increased intelligence), but maladaptive when old (Alzheimer's) ). If you've wondered why brilliant folks get Alzheimer's, it seems it's not in *spite* of the brilliance but both can come from the same genotype (but remember that genes are not destiny)