I've read three different medical studies in the past 1-2 years regarding approaches to memory/cognition. All 3 studies showed a clear and decisive benefit due to the exact same thing: cardiovascular activity 4-5 days or more a week. It wasn't even close. No benefits seen in any OTC products / herbal products (Prevagen). The exercise significantly improved outcomes over prescription medicines like Aricept, and also over other long presumed benefits like "exercising your brain" with sudoku, puzzles, etc.
Also of interest is how cardiovascular exercise can help improve symptoms of Parkinsons.