by Jack Norris, RD
Vitamin B12 is arguably the most important nutrient in vegan nutrition. B12 is found in meat, dairy, and eggs. In contrast, there are no reliable plant sources of B12. Luckily, B12 doesn’t need to be obtained from animal foods because it’s made by bacteria. B12-fortified foods are widely available in many countries and B12 supplements tend to be common and inexpensive. The discovery of vitamin B12 in the 1940s allowed veganism to become a realistic lifestyle.
The overwhelming consensus in the mainstream nutrition community and among vegan health professionals is that B12 supplementation is necessary for the optimal health of vegans. The good news is that vegans who supplement with B12 often have a superior B12 status to meat-eaters.
But what if a vegan feels fine and so doesn’t bother supplementing with B12?
B12 is normally needed for red blood cells to divide and become active and if B12 intake is low an overt deficiency can manifest through fatigue, known as macrocytic anemia or megaloblastic anemia. B12 also protects the nervous system and without it someone can develop tingling in the hands or feet. If not treated, the deficiency can progress to more serious symptoms such as blindness, deafness, and dementia.
To further complicate matters, someone can develop subclinical deficiency which manifests as elevated homocysteine levels. Homocysteine is a potentially toxic byproduct of protein metabolism that the body clears with the help of B12. Elevated homocysteine levels have been consistently associated with an increased risk of cognitive decline, cardiovascular disease (especially stroke), and early mortality; there’s also a link with low bone mineral density. Many studies have found a high prevalence of elevated homocysteine among vegans who don’t supplement with B12. In contrast, vegans who supplement with B12 have healthy homocysteine levels (details in Homocysteine and Mild B12 Deficiency in Vegans).
A 1955 study from the U.K., one of the earliest studies of vegans, found a high prevalence of B12 deficiency with some vegans suffering from nerve damage and dementia. There have been many documented cases of individual vegans developing overt B12 deficiency symptoms after a period of not supplementing (see Individual Cases of B12 Deficiency in Vegans). And I’ve personally known numerous vegans who neglected B12 and subsequently experienced fatigue and temporary neuropathy that resolved upon supplementation.
If you look further into the details of vitamin B12, you’ll quickly find that they’re expansive and complicated. But one thing is simple: Vegans should ensure a reliable source of B12.
There are many options for meeting B12 recommendations, depending on how often you take B12 or eat fortified foods. The table below shows options for meeting the U.S. Institute of Medicine (IOM) recommended dietary intake or the European Food Safety Authority (EFSA) adequate intake. We explain how these amounts were calculated in our Rationale for Recommendations.
The recommendations above are for the cyanocobalamin form of B12 which is the form used for most fortified foods and many supplements. Cyanocobalamin is the form that we recommend because it’s more stable and has been researched more thoroughly than other forms. The hype around the other forms of B12 is mostly propaganda from the supplement industry. For more information on the forms, see Coenzyme Forms: Methylcobalamin and Adenosylcobalamin.
- B12 is normally measured in micrograms, which can be abbreviated as either µg or mcg. 1,000 micrograms equals 1 milligram (mg).
- If you haven’t had a regular source of B12 for more than a few months, take 2,000 µg once a day for 2 weeks to replenish your stores.
- While there’s no definite cutoff for when larger amounts of B12 become unsafe, we somewhat arbitrarily recommend not taking more than 1,000 µg per day over the long-term without guidance from a physician.
- Large doses of B12 can trigger acne-like symptoms in a small number of people.
- To increase absorption, we recommend chewing B12-only supplements and swallowing multivitamins whole.
- People with kidney disease or a suspected B12 deficiency or malabsorption should talk to their doctors about an appropriate B12 regimen.
- In March of 2020, the Daily Value for B12 on food nutrition labels in the United States was lowered from the 1968 RDA of 6 µg to the current RDA of 2.4 µg.
- Store B12 supplements and fortified foods in a dark, cool place, preferably a refrigerator. Exposure to light can damage B12.
- B12-fortified toothpaste is available in some locations and has been shown to be a reliable source of B12 for vegans.
- Can a Natural Diet Require Supplements?
- What Every Vegan Should Know about Vitamin B12: An Open Letter from Health Professionals and Vegan Organizations
Research on Vitamin B12
The links below provide a thorough review of the scientific literature on vitamin B12 and the vegan diet.
- Brief History of B12 Recommendations for Vegans
- Government Recommendations
- Institute of Medicine’s Recommendations
- European Food Safety Authority’s Recommendations
- Cyanocobalamin Absorption
- Vegan Health B12 Recommendations
- Appendix A. Minimizing Methylmalonic Acid Levels
- Appendix B. Clinical Trials: Impact of B12 Supplementation on Metabolites
- Serum B12
- Methylmalonic Acid
- Notes on Clinical Trials of B12 Supplementation
- Appendix C. Factorial Approach
- Appendix D. Pregnancy and Breastfeeding
- Appendix E. IOM Recommendations for People Over Age 50
- Appendix F. ASMBS B12 Recommendations for People after Bariatric Surgery
- Clinical Trials in Nonvegetarians
- Extrapolating Wolters et al.’s Findings to Vegans
- Observational Studies
- B12 Malabsorption
- Degradation of B12 under Experimental Conditions
- Yamada et al.’s 2008 Study of B12 in Fortified Beverages and Multivitamins
- Kondo et al. and Herbert et al.’s Research on Multivitamins circa 1980
- Potential Improvements in the Accuracy of Nutrition Labeling
- B12 Transport Proteins and Multivitamins
- Observational Study of B12 in Fortified Non-Dairy Milks
- Anecdotal Reports
- Dangers of Recommending “Take a Multivitamin”
- Appendix A: Personal Experiment
- PREVEND Raises Concern
- Negative Outcomes in Vitamin B12 Supplementation Trials
- Vitamin B12 and Cyanide
- Cyanocobalamin and Kidney Disease
- B12 Amounts Versus B12 Activity
- Microbiological Assay
- R-protein Assay
- Intrinsic Factor Assay
- Intrinsic Factor Assay Shown to Be Unreliable in Humans
- Ochromonas Malhamensis Fares Better Than an Intrinsic Factor Assay
- Paper Chromatography
- Methods for Measuring B12 Activity of a Food
- Bacterial Contamination
- Plant Foods with Practically No Detectable B12 Analogue
- Fermented Foods
- Mankai (Duckweed)
- Seaweeds (Macroalgae)
- Soil and Organic Produce as a B12 Source for Vegans
- Background on Homocysteine
- Homocysteine in Vegetarians and Vegans
- B12 Status and Prospective Studies of Cognitive Decline
- B12 Metabolites and Brain Volume
- Randomized Controlled Trials of B-Vitamins, Cognitive Decline, and Brain Atrophy
- Research on Vegetarians and Vegans
- Summary of B12 and Cognition
- Mortality and Cardiovascular Disease
- Bone Mineral Density