Vitamin B12
Below is summary of what people on a plant-based diet should know about vitamin B12. For more detailed information, see:
- Vitamin B12 Recommendations for Vegans and Near-Vegans.
- Vitamin B12: Are You Getting It? by Jack Norris, RD
- What Every Vegan Should Know about Vitamin B12 by Health Professionals & Vegan Organizations
There are a number of myths about vitamin B12. Some vegan advocates emphasize that humans need only small amounts of B12 and that it can be stored in the body for years. It is true that, at the time they become vegan, some people have enough B12 stored in their liver to prevent overt B12 deficiency for many years. However, people often misinterpret this to mean that you only need to consume a tiny amount of B12 once every few years. Actually, to build up such stores, it takes many years of consuming B12 beyond one's daily needs. Many people do not have large enough stores of B12 to be relied upon even for short periods. This is an easy problem to solve by simply eating B12-fortified foods or taking a supplement.
There are no reliable, unfortified plant sources of vitamin B12 (see B12 in Tempeh, Seaweeds, Organic Produce, and Other Plant Foods for more information); therefore fortified foods and/or supplements are necessary for the optimal health of vegans and even vegetarians in many cases. Luckily, vitamin B12 is made by bacterial fermentation such that no animal foods are necessary to provide it.
There are two types of B12 deficiency: overt and mild.
Overt vitamin B12 deficiency:
B12 protects the nervous system. Without it, permanent damage can result (e.g., blindness, deafness, dementia). Fatigue, and tingling in the hands or feet, can be early signs of deficiency. B12 also keeps the digestive system healthy and an overt deficiency can cause digestive problems.
Mild vitamin B12 deficiency:
By lowering homocysteine levels, B12 reduces the risk of heart disease, stroke, and other diseases. Vegans and near-vegans who do not supplement with vitamin B12 have consistently shown elevated homocysteine levels.
From 1999 to 2003, there were many studies comparing the homocysteine levels of vegans and vegetarians who do not supplement their diet with vitamin B12 to those of non-vegetarians. In every study, the vegans or vegetarians had higher homocysteine levels than the meat-eaters and in the range associated with an increased risk of heart disease and stroke.
In contrast, one study compared vegans who supplemented their diets with vitamin B12 (an average of 5.6 mcg/day) with non-vegetarians. Their homocysteine levels were the same, and well within the healthy range. Details can be read in the section Homocysteine, B12, Vegetarians, and Disease of Vitamin B12: Are You Getting It?
If you have been a typical meat eater for most of your life, your body should have stored enough B12 to prevent overt deficiency for a number of years. However, when B12 intake is zero, old B12 stores cannot be relied on to keep homocysteine levels in check.