Stop believing the myths about vitamin B12 on a vegan diet that are putting your health at risk. Embrace the reality that vitamin B12 is a nutrient of concern on a vegan diet because there are no reliable sources of this vitamin naturally occurring in plant-based foods.
- What is Vitamin B12?
- What Does Vitamin B12 Do in the Body?
- Daily Intake Requirements of Vitamin B12
- Vitamin B12 Deficiency
- How to Consume Enough Vitamin B12 as a Vegan
- Vitamin B12 Supplements for Vegans
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What is Vitamin B12?
Vitamin B12 is a water-soluble vitamin and an essential nutrient. Essential nutrients are any compound that our bodies cannot make; therefore, we must consume all the essential nutrients through diet.
Vitamin B12 is also called cobalamin. The structure of vitamin B12 always contains a cobalamin molecule. Different molecules attach to the cobalamin and form various analogues of vitamin B12. Some analogues are active in the body, some are not, and some inactive analogues can be converted into active analogues by the body. Only two analogues of vitamin B12 are active in the body: adenosylcobalamin and methylcobalamin.
Cyanocobalamin is the vitamin B12 analogue often found in supplements. It is readily converted to both active B12 analogues in the body. There is also hydroxocobalamin, found in foods, and it too can be converted into an active form of vitamin B12 by the body. All other analogues of vitamin B12 (aka cobalamin molecules) are considered inactive, because they cannot be converted into one of the two active vitamin B12 analogues.
These inactive analogues are present in many different foods but do not count towards vitamin B12 intake requirements as they do not become active in the body.
What Does Vitamin B12 Do in the Body?
Vitamin B12 acts as a coenzyme. This means vitamin B12 works together with other molecules, called enzymes, to help them perform their intended role in the body. Enzymes are an important group of molecules that allow specific reactions to happen in the body.
There are three main functions of vitamin B12:
- DNA Production and Healthy Red Blood Cells: Vitamin B12 is part of a metabolic pathway that creates molecules needed for DNA production. This pathway enables production of healthy red blood cells.
- Homocysteine Conversion: This same metabolic pathway uses vitamin B12 to convert homocysteine into other molecules. Homocysteine is toxic to the body if it builds up.
- Healthy Nerve Cells: Vitamin B12 is needed for healthy nerve cells and may be related to healthy aging of the brain.
Daily Intake Requirements of Vitamin B12
The recommended dietary allowance of vitamin B12 for adults is 2.4 mcg per day 1. Absorption of vitamin B12 tends to decrease with age so there is some debate that the recommendation should be increased for adults over the age of 65.
The value of 2.4 mcg is recommended because it’s the amount of vitamin B12 needed to prevent macrocytic anemia, a common sign of vitamin B12 deficiency 1.
However, vitamin B12 does more than just prevent anemia and recent research suggests a need for a higher daily intake, for optimal health. An intake of 4-7 mcg of vitamin B12 from food sources was found to produce optimal levels of vitamin B12 biomarkers, including homocysteine and methylmalonic acid, in healthy adults 2.
Doses of vitamin B12 above the recommended level are generally considered safe 1. There is no upper limit set for the intake of vitamin B12, meaning an intake of 4-7 mcg or more per day should be safe 1, 2. Always talk with your doctor or dietitian before starting/ changing any supplements.
Vitamin B12 Deficiency
With vitamin B12 deficiency, any or all of the three main functions of vitamin B12 can go awry, causing:
- Macrocytic Anemia: This is the "classic" outcome of vitamin B12 deficiency. Macrocytic anemia means that red blood cells did not divide properly and are too large to function.
- Homocysteine Buildup: Homocysteine buildup is associated with increased risk of heart disease and Alzheimer's disease 3, 4. It's possible to not have any signs or symptoms of vitamin B12 deficiency and still have elevated homocysteine levels.
- Nerve Damage: Vitamin B12 deficiency has the potential to cause irreversible, permanent nerve damage 5. Vitamin B12 is needed to produce myelin which acts as an insulator for nerve cells. Without myelin, nerves don't function properly (and the nerve cell can then die) 5.
Signs and Symptoms of Vitamin B12 Deficiency
As a quick reference, here’s a list of signs and symptoms for vitamin B12 deficiency 6:
- Fatigue, loss of energy
- Tingling/ numbness in hands and feet
- Reduced sensitivity to pain/ pressure
- Blurred vision
- Abnormal gait
- Sore tongue
- Poor memory
- Personality changes
- Macrocytic anemia
- Faulty digestion, diarrhea
- Lack of appetite
- Loss of menstruation
If you have any of these symptoms, see a doctor for diagnosis immediately. Nerve damage from vitamin B12 deficiency can become severe and permanent. All of these signs and symptoms can also be caused by other conditions, some of which may be serious.
How to Consume Enough Vitamin B12 as a Vegan
Food sources of vitamin B12 for vegans include:
- Fortified nutritional yeast
- Fortified non-dairy products (ex. soy milk, almond milk)
- Fortified meat alternatives (TVP, soy-based meats), breakfast cereals etc.
As you can see, the key here is fortification. As a vegan you can choose to eat an adequate intake of B12 fortified foods or take a vitamin B12 supplement.
There is a lot of misinformation about vitamin B12 out there. To clear things up:
- Vegan foods that may contain vitamin B12 are said to be: fermented foods (tempeh, miso, fermented tea, kombucha), algae (chlorella, spirulina), seaweeds (nori), and organic plants (fruits and vegetables).
- None of these foods have been shown (in research studies) to be a reliable source of vitamin B12.
- For a food to be considered a reliable source of vitamin B12, it needs to consistently improve vitamin B12 levels in people and needs to show that it has vitamin B12 activity in the body. There are lots of analogues of the B12 molecule that do nothing for the body.
- Fortified foods and vitamin B12 supplements are the only reliable sources of vitamin B12 for vegans.
Vitamin B12 Supplements for Vegans
As noted above, the recommended dietary allowance for vitamin B12 is 2.4 mcg per day 1. There is little evidence about vitamin B12 requirements for people relying on supplements alone, including vegans. One study found that a daily supplement of 2 mcg or 10 mcg per day was not enough to lower homocysteine levels to an ideal range 7.
There’s also a limit to how much vitamin B12 the body can absorb at once. High doses of vitamin B12 saturate the body’s mechanism for absorption. This means you absorb a smaller percent of vitamin B12 as the dose increases.
I have seen varying recommendations for the amount of vitamin B12 vegans need to supplement. I personally value the rigorous research that went into the B12 supplement recommendations on veganhealth.org. The author has taken all available research into account, including absorption rates of vitamin B12. Other expert vegan dietitians agree with these recommendations 8. To summarize the findings, vegans have 3 options for meeting their vitamin B12 requirement:
- Consume 2 servings of foods fortified with 2.0-3.5 mcg of vitamin B12 each day, at different times in the day (4-6 hours apart).
- Take a daily vitamin B12 supplement (cyanocobalamin) of 25-100 mcg each day.
- Take a vitamin B12 supplement (cyanocobalamin) of 1,000 mcg two times each week.
Adults over the age of 65 may need higher doses of 500 to 1000 mcg of vitamin B12 supplement each day. Always speak to a doctor before starting any supplements.
These recommendations are specific to cyanocobalamin supplements. Cyanocobalamin is the most stable form of vitamin B12 and is almost exclusively used in research studies about vitamin B12 supplementation. Therefore, the recommendations for vitamin B12 supplementation are based on taking cyanocobalamin.
There are other forms of vitamin B12 supplements on the market. The primary alternative is methylcobalamin. Research on the effectiveness of methylcobalamin as a vitamin B12 supplement is limited. However, it seems that very high doses of methylcobalamin, 1,000-2,000 mcg per day (compared to 25-100 mcg per day of cyanocobalamin) are needed for optimal vitamin B12 status 8, 9. There’s no evidence to suggest that methylcobalamin is superior to cyanocobalamin 10.
Summary: Vegan Vitamin B12
Vitamin B12 is an essential nutrient that's not found naturally in plant-based foods. Therefore, vegans need supplementation to avoid the risk of vitamin B12 deficiency. Always speak to your doctor or dietitian before starting new supplements or changing your supplement routine. Working with a vegan Dietitian can set you up for success on a vegan diet and give you the confidence to live a healthy lifestyle long-term!
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- Dietary Reference Intakes Tables
- Daily intake of 4 to 7 microg dietary vitamin B-12 is associated with steady concentrations of vitamin B-12-related biomarkers in a healthy young population
- Role of homocysteine in the development of cardiovascular disease
- Hyperhomocysteinemia and Alzheimer's disease: A systematic review
- Neuroenhancement with Vitamin B12—Underestimated Neurological Significance
- Associations of lifestyle and vascular risk factors with Alzheimer's brain biomarker changes during middle age: a 3-year longitudinal study in the broader New York City area
- Effect of physiological doses of oral vitamin B12 on plasma homocysteine: a randomized, placebo-controlled, double-blind trial in India
- Vitamin B12: A Vegan Nutrition Primer
- Methylcobalamin and Adenosylcobalamin
- Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency
Please note that this is a curated list of references for the topics above and is not intended to be comprehensive.
Disclaimer: always speak with a doctor before changing your diet. Please read our full website disclaimer.
Author Profile: Nicole Stevens
Nicole is a vegan Registered Dietitian (RD) and founder of Lettuce Veg Out. She provides vegans with balanced meals and easy-to-understand nutrition science.
Having attained a Masters degree and passing a national registration exam, Nicole is a trusted source of nutrition information. She uses this knowledge to educate others about vegan diets and how to thrive as a vegan.