To me, vitamin B12 is a weird one, because it's in so many foods that (unless you're vegan in which case you already know all this stuff and do other clever things) you're likely to get way more vitamin B12 in your diet than you need. But it's in every running list as an essential vitamin for runners!

B12 keeps your blood cells and nerves healthy, without it you can feel extremely tired, have low energy or weak muscles, depression, or even pins and needles and a sore tongue. In many ways it’s similar to iron, and B12 was even discovered when medical professionals were looking for cures for anaemia. 

If you do have a B12 deficiency, it might not even be because of a lack of B12 in your diet. For B12 to be absorbed you need “intrinsic factor” in your intestinal tract, which is a substance made in your stomach. B12 can only be made by bacteria which
is why it’s found in foods that come from animals. It’s chemical structure is really different from any other vitamin, and it contains cobalt!

Good sources of vitamin B12 (copied and pasted from www.webmd.com) are;

  • Beef, liver, and chicken
  • Fish and shellfish such as trout, salmon, tuna fish, and clams
  • Fortified breakfast cereal
  • Low-fat milk, yogurt, and cheese
  • Eggs