Here is a recent review of over the counter supplements for memory; I was happy to see a favorable view of curcumin and lion's mane:

Over the Counter Supplements for Memory: A Review of Available Evidence - PubMed (nih.gov)​

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Multi-vitamin supplements have been found to be beneficial:

Multivitamin Supplementation Improves Memory in Older Adults: A Randomized Clinical Trial - PubMed (nih.gov)

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Among curcumin supplements, one specific form has a published Alzheimer's study, and previous research done at UCLA with predementia:

Theracurmin Supplementation May be a Therapeutic Option for Older Patients with Alzheimer's Disease: A 6-Month Retrospective Follow-Up Study - PubMed (nih.gov)