Vitamin B12 (cobalamin)
A water-soluble vitamin essential for red blood cell formation, the nervous system and DNA synthesis, found almost exclusively in animal products.
B12 is unique among vitamins: it contains a cobalt atom (hence “cobalamin”) and is made only by micro-organisms (bacteria, archaea). Animals accumulate it by eating these bacteria or through their own gut flora.
An original angle: no plant produces B12. Vegans must supplement; it is not optional. The false plant sources (spirulina, seaweed, unfortified yeast) contain inactive analogues (pseudo-B12) that can even block receptors and worsen the deficiency.
A fascinating historical fact: our ancestors probably got some B12 from unfiltered water (rich in bacteria) and less “clean” food. Modern hygiene has removed this incidental source.
Deficiency sets in slowly (the liver stores 3 to 5 years of reserves), which makes it tricky: the symptoms (fatigue, tingling, cognitive problems, anaemia) appear late, sometimes after irreversible nerve damage.
Groups at risk beyond vegans: older people (reduced absorption), people on metformin (diabetes) or PPIs (acid-suppressing drugs), which block absorption. B12 needs intrinsic factor (a stomach protein) to be absorbed; without it (gastritis, surgery), even a meat-based diet is not enough.