Unfortunately you cannot obtain Vitamin B12 from a plant source. You must consume an animal product to get B12, which is a problem for vegans. In this case it is important to supplement a vegan diet with a B12 supplement. Commercially made B12 supplements are vegan as they are produced from bacteria.

A long term B12 deficiency can cause neurological damage, poor brain function, memory loss and anemia. B12 is also crucial in liver function.

Some vegans feel they can Spirulina to help with a B12 deficiency. Unfortunately the Methylcobalamin B12 found in Spirulina is in a very small amount and very hard to utilize.