Vitamin B12. Computer model of a molecule of vitamin B12. Atoms are represented as spheres and are colour-coded: carbon (yellow), hydrogen (white), nitrogen (blue) and oxygen (red). At centre is a cobalt ion (pink). Humans are unable to produce vitamin B12 and so must obtain it from their diet, it is found in meat, poultry, fish and dairy products. It is needed for the production of red blood cells and for a healthy nervous system. Deficiency of vitamin B12 leads to pernicious anaemia, which causes tiredness, dizziness, reduced sense of taste and a reduced sense of vibrations.