For many vegans,
vitamin B12 is
the issue. More controversy exists over this
nutrient than any other. The short story is this:
Vegans need to supplement their diet with vitamin B12 or risk deficiency. There is really very little disagreement about this among health professionals with expertise in
vegan diets. Even so, questions and misinformation about vitamin B12 continue to make the rounds among vegans.
All vitamin B12 comes from bacteria. These bacteria live in the soil and in the intestines of animals. The B12 they produce gets incorporated into animal tissue and animal products such has milk and eggs. Thus, animal products become a source of B12 for humans. Bacteria on the outside of plant foods also produce B12 and theoretically, when these foods are consumed, they can provide humans with B12. Realistically, normal cleaning of food eliminates most of the available B12; consequently, these foods are not a reliable source.
Some vegans are loathe to believe that they need supplements or fortified foods to meet B12 needs. In some cases, this might reflect a desire to believe that vegan diets are natural and sufficient without supplementation. Historically, vegan diets probably were completely adequate, and there is reason to believe that humans were perfectly suited to do without nonvegan food sources of B12. The requirement for vitamin B12 is infinitesimal - only 2 micrograms a day. In fact, one teaspoon of vitamin B12 would meet the needs of nearly one hundred people for the rest of their lives! In addition, our bodies hoard B12 by storing any excess and by recycling what is used. The fact that it is saved, combined with the minimal amount required, suggests that we evolved to live healthfully in a B12-poor environment. Without animal foods in the diet, we probably did just fine on the little bits of B12 we picked up here and there through contamination of food and water. In many parts of the world, this is still probably sufficient to meet B12 needs. Potential problems exist for Western vegans, however, because our food supplies are well sanitized, and contamination with B12-producing bacteria is less likely. Of course, there are many advantages to eating clean food, so any inconvenience over B12 is a small price to pay.