Excerpt from http://www.earthsave.bc.ca/materials...ealth/b12.html

"We only need tiny amounts of B12 because the vitamin is stored and conserved so well by our bodies. According to a study published in the American Journal of Clinical Nutrition it is recommended that we get 2 g of B12 a day . This includes a large safety margin; the Physicians Committee for Responsible Medicine suggests we really only need 1 g a day. The official recommended daily intakes are 1 g in Canada and 2 g in the United States . Again, these figures have large safety margins built in. For most of us, excess B12 can be stored in our bodies for three years, although this varies. Dr. Michael Klaper suggests that anyone who has been vegan for more than three years should get their B12 level checked. If it is below 130 picograms per millilitre then you should make a conscious effort to add more B12-containing plant foods or supplements to your diet.

As yet, there are no known risks of consuming too much Vitamin B12 but there are some serious risks if our bodies don't absorb enough of it over a long period of time. That's because B12 is involved in some pretty important functions. Mainly, it's critical in the formation of red blood cells and the function of the nervous system. In particular, it plays a role in cell division and helps maintain the protective sheaths surrounding nerve fibres. It is also involved in the metabolism of certain amino acids and fatty acids . Over time, if someone is not getting enough B12 they can develop a type of anaemia in which red blood cells do not mature properly. Although very rare, severe deficiencies can lead to nerve and spinal cord damage. Some earlier symptoms of B12 deficiency include weakness; fatigue; difficulty with balance when walking; a numb, tingling in the fingers and toes like "pins and needles;" confusion; an inability to concentrate, and changes in the colour and surface of the tongue.

The Bottom Line: Are Vegans at risk?
By far, the most common cause of B12 deficiency is not the lack of the vitamin in the diet, but a problem in absorbing it, caused by a lack of a chemical in the body called the intrinsic factor. Doctors can easily test whether a person has a normal ability to absorb B12. For those who do not, no amount of the vitamin in the diet will help, and periodic injections of B12 will be necessary. Although there have been some reports of adult vegans with anaemia and nerve irritation as a result of their diet, these cases are very rare. A 1986 study of vegans by Dr. Milton G. Crane, MD did show that the serum levels of B12 of some of the subjects bordered on amounts that could be inadequate in some people . Another study by the British hematologist, Dr. Frey Ellis, and Dr. T.A.B. Sanders showed most vegans to have generous amounts of Vitamin B12, even though B12 tablet supplements were not used. So, while deficiency in vegans is possible, and the consequences serious, they are easily prevented according to Dr. Klaper by having a reliable source of B12 three times a week. There is still much to be learned about Vitamin B12 but one thing is certain: for most people a well-planned vegan diet can supply all the adequate nutrition needed for a long, happy and healthy life.

Special needs for pregnant women and young children
Pregnant and nursing women need to make sure that both they and their newborns get a reliable source of B12 in their diets every day. Babies need it every day because they don't yet have the stores of the vitamin to draw on like adults do. B12 needs to be in the mother's diet every day during pregnancy and lactation to allow for the child's growth and development. Dr. Klaper suggests infants get 0.5 g daily while pregnant and nursing Moms need 4 g daily. Most baby formula is fortified with B12 and tablets can always be crushed and added to food for infants."