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Head to the dairy aisle for this plentiful source of vitamin B12. In 2011 scientists found that people with indications of a B12 deficit performed worse on tests of long-term memory. Study author Christy Tangney, PhD, says too little B12 can lead to the degeneration of myelin sheaths—the protective layer around our nerves that allow impulses to travel quickly through the brain.

An alternative: Swiss cheese.