3 Answers

Try fish oil capsules

Maximize the use of your brain - use it, don't lose it!

I enjoy puzzles, Sudoku, for example.  My mom does word searches.  There are lots of math and word puzzles and books filled with them.  A good way to increase your memory is to play games that require you to focus on memory.  A simple card game like Concentration, a free phone app. called "Brain Age Analyzer".  There is a game played in a small group where the first person says a thing that starts with the letter "a".  Next person repeats the "a" word and adds one that starts with "b".  Next one repeats the "a" and "b" words and adds a word the starts with "c".  And so it goes.  
Taking a class in American Sign Language, singing songs, memorizing poems or verses. Repetition is retention.