B12 is an exceptional vitamin. It is required in smaller amounts than any other known vitamin. Ten micrograms of B12 spread over a day appears to supply as much as the body can use. In the absence of any apparent dietary supply, deficiency symptoms usually take five years or more to develop in adults, though some people experience problems within a year. A very small number of individuals with no obvious reliable source appear to avoid clinical deficiency symptoms for twenty years or more. B12 is the only vitamin that is not recognized as being reliably supplied from a varied wholefood, plant-based diet with plenty of fruit and vegetables, together with exposure to sun. Many herbivorous mammals, including cattle and sheep, absorb B12 produced by bacteria in their own digestive system. B12 is found to some extent in soil and plants. These observations have led some vegans to suggest that B12 was an issue requiring no special attention, or even an elaborate hoax. Others have proposed specific foods, including spirulina, nori, tempeh, and barley grass, as suitable non-animal sources of B12. Such claims have not stood the test of time.
In over 60 years of vegan experimentation only B12 fortified foods and B12 supplements have proven themselves as reliable sources of B12, capable of supporting optimal health. It is very important that all vegans ensure they have an adequate intake of B12, from fortified foods or supplements. This will benefit our health and help to attract others to veganism through our example.