Evidence-Based Nutrient Recommendations

Vitamin B12


by Jack Norris, RD

For the last few months, I was feeling sluggish, had to lie down a couple of times a day, found it difficult to work evenings and to exercise for long periods. Under [an] MD’s guidance, I was taking protein powder, creatine, testosterone, nystatin, etc., all to no avail. I was taking nutritional yeast every day, so I knew it wasn’t B12 deficiency. Then, one day, I came across your B12 article by sheer accident. I wasn’t going to read the whole thing, but I glanced through it and was struck by your insistence that none of the usual sources are adequate. I still didn’t believe it, but I had some old B12 pills in the fridge, so I popped one. The effect was almost immediate and remarkable. I have been taking them almost every day, my stamina and energy level are up, and I feel middle-aged again instead of a tired old man.

–Alex Hershaft, PhD, President of Farm Animal Rights Movement

Vitamin B12 is a complicated vitamin with unique absorption mechanisms and four active analogs. There are also a number of inactive analogs, pseudovitamin B12, that can possibly interfere with its function.

Vitamin B12 is found in meat, dairy, and eggs. In contrast, there are no reliable plant sources of B12 other than fortified foods. Luckily, vitamin 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 vitamin B12, and taking B12 on a regular basis will provide you with a B12 status equal to or superior to people who rely on animal products for B12. But what if you don’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.

Despite the overwhelming evidence, 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 in their livers to prevent overt B12 deficiency for many years, markers of B12 deficiency usually start to increase abnormally within a few months.

Overt B12 Deficiency

B12 protects the nervous system and without it permanent damage can result (e.g., blindness, deafness, dementia). Fatigue and tingling in the hands or feet are often the early signs.

Vitamin B12, like folate (aka folic acid), is needed to help red blood cells divide. In some cases, vegans may get so much folate that even with B12 deficiency, their blood cells continue to divide properly. But in other cases, a vitamin B12-deficient vegans’ blood cells will fail to divide properly and they’ll become fatigued due to macrocytic anemia, also known as megaloblastic anemia.

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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