B12 is an essential nutrient for human health. Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis.You need to consume adequate amounts to avoid megaloblastic anemia and neurological disorders.
There are some people at increased risk of developing B12 deficiency; including older adults, people with gastrointestinal disorders, or people with pernicious anemia. Pernicious anemia affects less than 2% of the population, and those people are not able to adequately absorb Vitamin B12. Breastfeeding infants may also be at risk if their mother's stores of B12 are low.
There are no adequate plant-sources of B12— despite what you might have heard about eating “dirty” vegetables. Let’s start with the story behind that idea to better understand why it's critical to complement your plants with a B12 source.
We all know that human life relies on fertile soil. We don’t often realize that we rely on the life in our soil. One reason is that soil bacteria produce Vitamin B12. By consuming vegetables straight from the family garden, or foraged from the wild, humans have historically ingested trace amounts of B12. This is the reason that some people advocate not washing your vegetables in order to ingest the B12 that remains on the surface. In our super-sanitized world, we (or food producers) thoroughly wash food, which further reduces the chance of ingesting a sufficient amount of B12 through natural sources.
You may theoretically be able to derive B12 from dirty vegetables, but when you recognize the critical importance of B12, you realize that method is quite risky. You are essentially rolling the dice with a nutrient that is critical for neurological functions, for maintaining your immune system; and even for making blood cells and DNA. Consuming unwashed produce also increases the likelihood of ingesting pesticides and herbicides as well as potentially harmful bacteria. It is not advisable to depend on this method of obtaining B12.
Why is this a particular concern for plant-based people? B12 deficiency is common among people following a plant-based diet. In a review including 13 studies with vegan participants, 10 studies reported at least 20% of vegan participants were B12 deficient. If a human consumes other animals, they may obtain B12 from the meat. It is not that those animals naturally produce B12 — the Vitamin comes from bacteria — but those animals live in unsanitary environments, and they ingest more bacteria than humans, so the B12 accumulates in their tissues.
You can also find B12 in “fortified foods”— nutritional yeast is a great example; many breads, dairy-free milks, and cereals are also fortified. These fortified products, however, contain relatively low doses of Vitamin B12 compared to a supplement. This may be sufficient if you eat these products very regularly (nearly every day), but if you eat them only occasionally, it is worthwhile to complement your plant-based diet with a source of B12. Most doctors and dietitians are quick to agree with this recommendation.