Vitamin B12, molecular model. Vitamin B12 comprises a group of compounds that contain cobalt. Atoms are represented as spheres and are colour-coded: carbon (blue), hydrogen (gold), cobalt (dark red), nitrogen (dark blue), oxygen (red) and phosphorus (purple). Vitamin B12 is an essential nutrient that humans are unable to produce and so need to obtain from their diet. It is found in meat, fish poultry and dairy products. Vitamin B12 is needed for producing red blood cells and for a healthy nervous system. Deficiency can lead to pernicious anaemia, with symptoms including tiredness, dizziness and a reduced sense of taste.