Evidence-Based Nutrient Recommendations

Vitamin B12


by Jack Norris, RD

Vitamin B12 is the most important nutrient for vegans to be aware of. B12 is found in meat, dairy, and eggs. In contrast, there are no reliable plant sources of B12 other than fortified foods. Luckily, B12 is made by bacteria and so doesn’t need to be obtained from animal products.

It’s fairly easy for most vegans to obtain a source of B12, and taking it on a regular basis will provide someone with a B12 status equal to or superior to people who rely on animal products for B12. 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. This and many other Individual Cases of B12 Deficiency in Vegans, and a great deal of other research, has led to the overwhelming consensus in the mainstream nutrition community and vegan health professionals that vitamin B12 fortified foods or supplements are necessary for the optimal health of vegans. I’ve known many vegans who neglected B12 and subsequently experienced fatigue and temporary neuropathy that resolved upon obtaining a reliable source.

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 vitamin 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.

Mild B12 Deficiency

Homocysteine is a byproduct of protein metabolism that the body clears with the help of vitamin B12. Elevated homocysteine levels are linked with increased risks of dementia, heart disease, and stroke.

From 1999 to 2003, many studies found that vegans who weren’t supplementing with vitamin B12 had unusually high levels of homocysteine. In contrast, one study found that vegans who supplement with vitamin B12 (an average of 5.6 mcg/day) had homocysteine levels well within the healthy range.

What Vegans Need to Know

The most critical information to know is:

For other opinions, 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—it includes every important study on vegans published since 1980.

The B12 Molecule

Measuring B12 Status


Plant and Intestinal Sources

Vitamin B12 Supplements

  • Vitamin B12: Rationale for Recommendations
  • People Over Age 50
  • Oral Supplements for B12 Malabsorption
  • B12 Status of Vegans

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    • If you have a question about whether it's okay to cut supplements in half or combine supplements to achieve the dose we recommend, the answer is “Yes.” Be aware that nutrient recommendations are only estimates—it's not necessary to consume the exact amount we recommend every single day.
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    • We cannot provide personal nutrition advice for specific health conditions. If you need private counseling, here's a list of plant-based dietitians and we especially recommend VeganHealth contributor Taylor Wolfram, MS, RDN, LDN.
    • We urge you to consult with a qualified health professional for answers to your personal questions.

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