Folate (found naturally in vegetables and beans) and B12 (in animal products) help produce new cells. They also join forces to break down homocysteine, an amino acid that, at high levels, is linked to Alzheimer's disease. But too much folate and too little B12 may have a negative effect on your mental agility (in one study, people with this imbalance scored lower on cognitive function tests). So in this case, teamwork isn't a plus—it's simple prudence.
For breakfast, fill an omelet with spinach. For dinner, cook a salmon fillet with a side of asparagus, and try to limit the amount of alcohol you drink. (It can impede your body's ability to use the vitamins.)