Alike the other B vitamins, vitamin B12 (or cobalamin) plays an essential role in the production of energy. It is also important for proper red blood cell formation and neurological function as well as lowering homocysteine levels that decrease your risk of heart disease [I].
Vitamin B12 is an interesting vitamin within food sources because it is bound to protein (primarily animal protein). Once ingested, vitamin B12 is separated from protein by the activity of the hydrochloric acid and enzymes in the stomach. The B12 is then “free” to combine with another protein called intrinsic factor, which is secreted by the stomach's parietal cells. Once bound to intrinsic factor, it is absorbed and used by the body.
Most vitamins are made by plants and animals, which are absorbed when we eat them. But no plant or animal has been shown to be able to produce vitamin B12. The only source of this vitamin appears to be tiny bacteria! Animal products only contain B12 because they either eat the bacteria or the bacteria is produced in their rumen. This is why potential B12 deficiency is something vegans need to be acutely aware of.
Vitamin B12 Deficiency
Primary deficiency of this vitamin occurs when one's diet does not include foods containing vitamin B12. Secondary deficiency can occur when irritation and inflammation of the stomach prevents the stomach cells from producing intrinsic factor, which leads to the vitamin not being absorbed (known as pernicious anemia). Another factor that can contribute to secondary vitamin B12 deficiency is when the cells of the stomach reduce production of hydrochloric acid (hypochlorhydria). This happens frequently with the elderly and people who are under a lot of stress. B12 injections may be necessary when absorption through the stomach is not possible.
Vitamin B12 deficiency symptoms can include memory loss, fatigue, difficulty sleeping, and severe neurological dysfunction. Numbness, tingling, or itching in the extremities may also indicate a deficiency. Dementia and memory loss are sometimes treated with B12.
Recommended Daily Allowance (RDA)
Men 19 and older, 4 mcg/day
Women 19 and older, 2.4 mcg/day
Pregnant women, 2.6 mcg/day
Breastfeeding women, 2.8 mcg/day
Upper Level (UL), unknown
Food Sources of Vitamin B12
Animal sources: shellfish, fish, organ meats, and dairy in smaller amounts
3 oz fresh or canned clams— 84.1 mcg
3 oz cooked octopus— 30.6 mcg
3.5 oz smoked sockeye salmon— 18.1 mcg
3 oz blue fin tuna— 9.2 mcg
1 fillet rainbow trout— 9.0 mcg
1 medium oyster— 7.2 mcg
1 turkey giblet— 69.3 mcg
1 slice pan-fried beef liver— 67.3 mcg
3 oz rabbit meat— 7.1 mcg
3.5 oz beef cut tender medallions— 0.8 mcg
3.5 oz pheasant— 0.8 mcg
1 oz Swiss cheese— 0.9 mcg
1 oz gjetost cheese— 0.7 mcg
1 oz mozzarella— 0.6 mcg
Organic desiccated beef liver capsules is a phenomenal way to get your B12 needs met if organ meats aren’t your thing and you have a tendency to be low in B vitamins and B12. Beef liver capsules are also an excellent way to get your iron needs met as well.
Plant sources: laver (seaweed), miso, tempeh, tamari, and shoyu
Think of anything that is fermented by bacteria, and you most likely have a source of vitamin B12. However, the amounts of B12 in plant sources are very small.
A Note for Vegans
It is very controversial as to whether a healthy vegan diet supplies adequate amounts of B12. Cultured and fermented bean products like tempeh, miso, tamari, and shoyu may or may not contain significant amounts of B12, depending upon the bacteria, molds, and fungi used to produce them. The B12 content of sea vegetables can also vary depending on the distribution of microorganisms in the surrounding sea environment.
Incorporating fortified brewer's yeast can solve this problem. Brewer's yeast is made from a one-celled fungus called Saccharomyces cerevisiae, which is grown on sugar beets and is very rich in B vitamins. However, brewer's yeast does not contain significant amounts of B12 in itself. Brands fortified with B12 are available, so check the food label to make sure B12 has been added!
[I] Saposnik G, Ray JG, Sheridan P, McQueen M, Lonn E. “Homocysteine-lowering therapy and stroke risk, severity, and disability: additional findings from the HOPE 2 trial”. Stroke. 2009 Apr;40(4):1365-72. doi: 10.1161/STROKEAHA. 108.529503. Epub 2009 Feb 19. Web. June. 2016. <http://www.ncbi.nlm.nih.gov/pubmed/19228852?dopt=Abstract>.