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 is made by bacteria and doesn’t need to be obtained from animal products allowing vegans to obtain B12 through supplements and fortified foods.
But what if someone doesn’t bother?
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 becoming deficient. I’ve known many vegans who’ve neglected B12 and subsequently experienced fatigue and temporary neuropathy that resolved upon obtaining a reliable source. Research on non-supplementing vegans has shown them to have elevated levels of homocysteine which might increase the risk for cardiovascular disease and cognitive decline.
For these reasons, the overwhelming consensus in the mainstream nutrition community and among vegan health professionals is that supplementation is necessary for the optimal health of vegans.
Despite overwhelming evidence for the importance of vegans obtaining a consistent, reliable source of B12, some vegan advocates still believe that “plant foods provide all the nutrients necessary for optimal health,” and don’t address B12 when promoting the vegan diet. Others emphasize that humans need only small amounts of B12 and that it can be stored in the body for years, implying that there’s nothing with which to concern ourselves. While it’s true that at the time many people become vegan, they have enough B12 stored to prevent overt B12 deficiency for many years, markers of deficiency begin to increase shortly after intake stops.
If you look into the details of vitamin B12, you’ll quickly find out that they’re expansive and complicated. But one thing is simple: Vegans should ensure a reliable source of B12 according to the recommendations on our Daily Needs page.
Overt B12 Deficiency
Fatigue is a typical symptom of vitamin B12 deficiency. Vitamin B12 is normally needed for red blood cells to divide and become active. Without enough B12, fatigue can result due to a lack of oxygen-carrying capacity of the red blood cells. This condition is known as macrocytic or megaloblastic anemia.
B12 also protects the nervous system and without it, permanent damage can result, such as blindness, deafness, and dementia. B12-related nerve damage often manifests as tingling in the hands or feet and, if not treated, can progress to more serious symptoms.
To complicate matters, folate also helps red blood cells to divide. Many vegans obtain high amounts of folate from their diet and, due to a quirk in physiology, some vegans might get so much folate that even with a B12-deficiency their blood cells will continue to divide. This can mask a B12-deficiency, preventing the fatigue that can be an early warning sign.
Subclinical B12 Deficiency
Homocysteine is a byproduct of protein metabolism that the body clears with the help of B12. Many studies have found that vegans who don’t supplement with B12 have a high prevalence of elevated homocysteine without overt symptoms of deficiency.
There’s evidence that subclinical B12 deficiency and/or elevated homocysteine levels increase the risk of cognitive decline, cardiovascular disease (especially stroke), early mortality, and possibly low bone mineral density.
In contrast to vegans who don’t supplement with B12, vegans who supplement tend to have homocysteine levels well within the healthy range. More info can be found in Homocysteine and Mild B12 Deficiency in Vegans.
What Vegans Need to Know
The most critical information to know is how much B12 to take. We list our B12 recommendations the Daily Needs page, along with the most important notes about supplementing.
You also might be interested in our thoughts about the naturalness of a vegan diet in our article, Can a Natural Diet Require Supplements?
For opinions of health professionals not affiliated with VeganHealth, see this open letter from health professionals and vegan organizations, What Every Vegan Should Know about Vitamin B12.
Vitamin B12: Are You Getting It?
This article provides a thorough review of the scientific literature on vitamin B12 and the vegan diet.
Vitamin B12 Supplements
- Facts about Supplemental B12
- Vitamin B12: Rationale for VeganHealth’s Recommendations
- Brief History of B12 Recommendations for Vegans
- Government Recommendations
- Cyanocobalamin Absorption
- Vegan Health B12 Recommendations
- Appendix A. Minimizing Methylmalonic Acid Levels
- Appendix B. Clinical Trials: Impact of B12 Supplementation on Metabolites
- Appendix C. Factorial Approach
- Appendix D. Pregnancy and Breastfeeding
- Appendix E. IOM Recommendations for People Over Age 50
- Coenzyme Supplements: Methylcobalamin and Adenosylcobalamin
- Oral Supplements for B12 Malabsorption
- Are Multivitamins an Adequate Source of B12 for 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”
- Elevated Vitamin B12 Levels and Mortality
- PREVEND Raises Concern
- Side Effects and Negative Outcomes in B12 Supplementation Trials
- Vitamin B12 and Cyanide
- Cyanocobalamin and Kidney Disease
Measuring B12 Status
- Should I Get My B12 Status Tested?
Plant and Intestinal Sources
- Measuring B12: Why the Confusion?
- 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
- Vitamin B12 in Plant Foods
- Plant Foods with Practically No Detectable B12 Analogue
- Fermented Foods
- Mankai (Duckweed)
- Seaweeds (Macroalgae)
- Soil and Organic Produce as a B12 Source for Vegans
- Intestinal Bacteria as a Vitamin B12 Source
- Overt B12 Deficiency: Nerve Damage and Anemia
- Subclinical B12 Deficiency and Homocysteine in Vegans
- Background on Homocysteine
- Homocysteine in Vegetarians and Vegans
- Mortality and Cardiovascular Disease
- Bone Mineral Density
The B12 Molecule
- Vitamin B12 Analogues
- Vitamin B12 Absorption
- Coenzyme Functions
- Vitamin B12 and Nonhuman Animals
B12 Status of Vegans
- B12 Status of Vegan Infants and Toddlers
- B12 Deficiency Cases in Vegan Infants and Toddlers
- B12 Status of Vegan Children and Teenagers
- B12 Status of Vegan Adults
- B12 Status of Older Vegetarians
- B12 Status of Raw Foodist Vegans
- B12 Status of Macrobiotic Vegetarians
- B12 Status of Lacto-Ovo Vegetarians
- Individual Cases of B12 Deficiency in Vegans
- Immerman—The Exception