Vegan Diets and Vitamin B12

As more and more of my family, friends and clients choose a more plant-based diet the more questions I get about how to get all the nutrients you need. I am a believer in food first and that we can get most of what we need by eating a variety of foods but when it comes to eating a strict vegan diet, getting all the nutrients you need in adequate amounts through food becomes complicated and somewhat challenging. There are several myths going around such as “you can get enough B12 by eating the dirt on your fruit and vegetables if you don’t wash them” and “the bacteria in your mouth produce all the B12 you need”. Clearly B12 needs a little clarification.

Function of B12

First off, B12 is a water-soluble vitamin critical in the production of the myelin sheath around nerves. It is also involved in DNA production and repair, red blood cell production and assists in the conversion of carbohydrates, proteins and fats from food into energy.

B12 Absorption

Simply put, digestion and absorption of B12 requires hydrochloric acid and pepsin to release B12 from the protein and activate it to bind with intrinsic factor secreted in the stomach. It is then absorbed in the small intestine into the bloodstream.


A B12 deficiency can occur due to the autoimmune disease pernicious anemia. A B12 deficiency can cause megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, soreness of mouth and tongue, weight loss, tingling hands and feet, depression, poor memory and others. Large intakes of folic acid (>1000mcg/d) can mask damaging neurological effects of B12 deficiency.

Natural Sources of B12

Vitamin B12 is synthesized by microorganisms and is therefore not found in plant foods. Natural sources include fish, meat, poultry, eggs, milk and dairy products. Some bacteria produce B12 in small amounts but not enough to support the needs of humans. Seaweeds have a B12 analogue (inactive form of B12). Fermented foods are not fermented through B12 producing bacteria and are therefore not a source. Chlorella may improve B12 status slightly but is unreliable.

Recommended Intake and deficiency

The RDA for B12 is 2.4 mcg/day for adults and 2.6 mcg/day for pregnant women. Vegetarians and vegans are both at risk, ask are pregnant women because requirements are slightly higher. Infants of women who are deficient in B12 are also at risk because B12 crosses the placenta and is found in breastmilk and if the mother is deficient the baby may become as well, increasing the risk for serious neurological damage.

Food Sources

Synthetic vitamin B12 called cyanocobalamin is added to some fortified plant-based foods such as tofu, soymilk, rice, almond and hemp milk. 1 cup contains 1 mcg. It is also added to breakfast cereals (1-6 mcg/serving), veggie burgers and dogs (1.2-4.2 mcg/serving). B12 is also found in Red Star Nutritional Yeast grown on a B12 rich medium.

To ensure you get enough, aim for 3 servings of B12 rich foods per day. 1 serving is ½ cup fortified beverage, 30g breakfast cereal, 42g fortified soy product (veggie burger) or 1 Tbsp nutritional yeast. You may also want to take a B12 supplement, B complex or multivitamin containing B12. Supplements should be 250mcg (100 x the RDA because ingested B12 supplements are only 1% absorbed. If absorption is compromised due to decreased production of intrinsic factor, intramuscular injections of cyanocobalamine can be administered.

The Bottom Line: If you are vegan be sure to check the labels on foods that may be fortified with B12 to ensure you are getting enough. If you don’t eat any foods fortified with B12 or just as insurance, it is a good idea to take a B12 supplement.

Vegan Diets and Vitamin B12 Vegan Diets and Vitamin B12 Vegan Diets and Vitamin B12 Vegan Diets and Vitamin B12