Vitamin B12
Why you need it: Vitamin B12 is vital for healthy nervous-system function and for the formation of DNA and red blood cells. It helps guard against anemia, a blood condition that causes fatigue and weakness.
Where to get it: Animal products are your best bet for B12. Cooked clams have the highest concentration of any food, with 84 micrograms (mcg) —a whopping 1,402% of your DV—in just 3 ounces. (One milligram equals 1,000 micrograms.) Vitamin B12 also occurs naturally in beef liver, trout, salmon, and tuna, and is added to many breakfast cereals.