Vitamin B12 and vegan diets - Lessons from
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 recognised 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.
Getting an adequate amount of B12
National recommendations for B12 intakes vary
significantly from country to country. The US recommended intake is 2.4 micrograms a day for ordinary
adults rising to 2.8 micrograms for nursing mothers. The German recommendation is 3 micrograms a day.
Recommended intakes are usually based on 50% absorption, as this is typical for small amounts from foods.
To meet the US and German recommendations you need to obtain sufficient B12 to absorb 1.5 micrograms per
day on average. This amount should be sufficient to avoid even the initial signs of inadequate B12 intake,
such as slightly elevated homocysteine and MMA levels, in most people. Even slightly elevated homocysteine
is associated with increased risk of many health problems including heart disease in adults, preeclampsia
during pregnancy and neural tube defects in babies.