Topics » Nutrition Science » 12 Questions Answered Regarding Vitamin B12
T. Colin Campbell Center for Nutrition Studies

Vitamin B12 is one of the most common topics I get asked about for those interested in a plant-based diet. I think we have a natural tendency to make sure we are getting enough of everything, and vitamin B12 is a legitimate concern for exclusively plant-based eaters, so it causes a fair amount of anxiety.

Because of this, I spent some time reviewing literature regarding B12 when I was writing my book The Campbell Plan, in which I discuss B12, other supplements, and many other hot topics as people transition to a plant-based diet. What you’ll learn is that B12 certainly need not cause anxiety once you have a little bit of understanding about the vitamin and what you should do to get enough.

Here is a conversation covering the basics. This is my interpretation of the evidence for general knowledge and should not be taken as medical advice. There are many clinical scenarios that might alter the advice below. Please discuss with your doctor.

How is B12 made?

B12 is made by anaerobic microorganisms (ie. bacteria that do not require oxygen to live). Anaerobic bacteria are common in the gastrointestinal tract of animals.

Vitamin B12

What foods might naturally contain B12?

  • Animal foods, including meat, milk, and eggs, contain B12 and are essentially the exclusive source of the vitamin in the American food supply (not counting supplements or fortification).
  • Two varieties of edible algae (Dried green (Enteromorpha sp.) and purple (Porphyra sp.) seaweed (nori)) have been found to have active B12, but other algae have inactive B12-analog compounds that have no apparent benefit in animal metabolism.
  • Some varieties of mushrooms and some foods made with certain fermentation processes have very small amounts of active B12.
  • Plants found in our food supply do not contain B12, though plants grown in experimental settings with B12-enriched soils or water (with hydroponic processes, for example) do actually take up B12.

How do animals get B12?

  • They absorb B12 made by their gut bacteria, in the case of ruminants like cows and sheep.
  • They eat poop (coprophagia), like some rodents do. (Please don’t get any bright ideas from this fact!)
  • They have bacterial contamination of their food.
  • They eat animal-sourced foods like other animal flesh, milk, or eggs.

I don’t eat my own poop, or anyone else’s poop. How do I get B12?

  • I’m pleased with your basic hygiene choices. But if you don’t eat animal-sourced foods, you aren’t getting B12 except through foods that have been artificially fortified with B12 (nondairy milks, cereals, etc.), which is potentially insufficient.
  • I mentioned a few rare plants or fermented foods before that may have B12, but I absolutely do not think these are a reliable way to get B12 for the average person.
  • This is why I recommend a daily supplement for those people with a reduced intake of animal foods.

Vitamin B12

Who is at risk for B12 deficiency?

  • Adults over the age of 50 who have atrophic gastritis (their stomach isn’t making as much acid) may not absorb B12 as well. This accounts for the majority of deficiency in older adults. Because atrophic gastritis may be relatively common, a B12 supplement or fortified foods are recommended by the Institute of Medicine for all adults over age 50, regardless of diet.
  • Many other conditions can predispose someone to B12 absorption problems: celiac disease, Crohn’s disease, pancreas dysfunction, history of bowel or stomach surgery, and others.
  • People with prolonged use of certain medications, including heartburn medicines such as proton pump inhibitors (like omeprazole, pantoprazole, etc…) and H2 blockers (like ranitidine, famotidine, cimetidine, etc…). Metformin, the common diabetes drug, may also lower B12 absorption.
  • People with reduced intake of animal foods

I don’t eat animal foods. How much B12 should I take?

  • Update on 5/10/18: For the general adult population, a daily dose of the smallest available tablet of B12 is more than sufficient. Recently, there has been some evidence that large dose B12 supplementation may be associated with an increase in cancer risk in some groups.[1] Because of these findings, and because I can’t find plain B12 supplements smaller than 500 mcg per pill, I’ve been recommending people take a multivitamin.* We only need about 2.4 mcg of B12 daily. So choose a multivitamin with a low level of B12 (perhaps 10-20mcg), and relatively low levels of everything else. Alternately, you can take the smallest dose of B12 you can find intermittently, perhaps every couple days, or a couple times a week, and get your blood levels checked to make sure it is sufficient. But don’t take a single large dose and expect to be loaded up for the next 6 months. It seems to be a good idea to take something at least weekly. Your body will absorb only a small amount of B12 in any pill. The reason for this low absorption is that there is only enough intrinsic factor (the body’s chemical that shuttles B12 into your gut cells) excreted per meal to absorb 2-4 micrograms of B12. In addition, your body absorbs B12 by passive absorption, but it does this with perhaps 1% of the total dose you consume (the percentage decreases with higher dosages).
  • I suggest a dosage just high enough to give you a nice low-average level of B12. I do not suggest B12 for anything other than to prevent deficiency.
  • For those with existing deficiencies or problems with absorption, you may need significantly higher doses. Please discuss this with your doctor.

What form B12 should I take?

  • Personally, I don’t really advise any particular form. You can take cyanocobalamin or methylcobalamin. Both have been shown to increase B12 levels. If any readers have seen primary research (ie. not a webpage like this one) that suggests a different interpretation, please let me know.
  • If you are concerned with deficiency or maximizing absorption, chewable or dissolvable tablets are much better absorbed. As discussed in my smoothie article that generated lots of lively debate, very important digestion starts in the mouth. This is another example.

Should I get blood levels checked?

  • For exclusively plant-based eaters, I suggest getting your B12 level checked every few years, particularly if you aren’t great about taking a supplement. I also suggest checking your methylmalonic acid (MMA) level, which is more specific for testing if you have enough active B12. Both are simple blood tests. This, like many other very specific suggestions in this article, are simply my interpretation of the information I’ve seen. There is no large database of studies, for example, that compares checking B12 yearly versus checking every 5 years. So this is just my best guess.

Should I take extra B12 for mega energy and other superior function?

  • No. I’m not aware of any evidence that supplementation does more than prevent deficiency.

What problems does B12 deficiency cause?

  • It classically causes a type of anemia (megaloblastic) and a neurological disorder (subacute combined degeneration). These are real and there are multiple unfortunate case reports in the literature of people, including young children, with permanent neurologic damage from B12 deficiency.
  • Symptoms of this type of anemia include: fatigue and weakness, weight loss, and sore tongue
  • Symptoms of this neurological disorder include: numbness and tingling of hands and feet, memory changes, poor balance, and depression
  • Infants can have developmental delay and failure to thrive (as an aside, these problems are almost always caused by other things)

Vitamin B12

When should I start supplementing a plant-based child who isn’t consuming animal foods?

  • First of all, congratulations on making an excellent health choice. I suggest all infants be exclusively breastfed for the first 6 months and that mom take a daily supplement so that her breast milk has B12. Formulas, if used, will contain B12.
  • Once baby stops getting a large portion of his or her calories from breast milk or formula, it probably is worth supplementing (Perhaps at age one? I don’t know. This depends on your circumstance). I suggest the smallest dose of B12, smashed up into an even smaller amount, and put in the food fed to baby. Many foods are already fortified with B12. Fortified foods may be sufficient if you carefully monitor how much baby gets.

Does our B12 requirement mean we aren’t pure herbivores?

  • At the risk of inciting ideological responses, here’s my answer: I believe it to be clear that humans did not evolve as strict vegans. From what we currently know, I believe our requirement for B12 supports this point of view. I believe that in the environment of scarcity we evolved in, we adapted to do quite well with a wide range of foods. That being said, we likely evolved from primarily plant-eaters millions of years ago and remain close genetic relatives to primarily plant-eating primates. Modern nutritional science has shown a dietary pattern dominated by unrefined plants, even exclusively containing plants, to be superior for prevention and reversal of chronic disease. Are we designed to be eating some insects, or some dirt, or some meat? Perhaps, but we don’t need to, and in our current environment of overabundance and profoundly sedentary lifestyles, I actually think this type of recommendation would do more harm than good.
  • Is it possible we’ll learn more information that changes the B12 conversation as we learn more about the gut microbiome? I’m not sure, but I sure hope so.
*Recommending a multivitamin is a recent change in my clinical practice. In the study I mentioned, there was a increased risk of cancer in users of isolated B12 supplements but no increased risk among users of multivitamins. Generally, multivitamins have a lower dose of B12, and though it’s just a guess, I think it is probably better to supplement regularly with low doses than take isolated megadoses less frequently. Sometimes you can find a multivitamin where two tablets or two capsules equals one dose. Even better! Just take one tablet or one capsule (in other words, half the multivitamin dose). You’re just looking for minimum levels to prevent deficiency. Let me be clear, though: a multivitamin will not prevent or treat chronic disease, increase your general well being if you are healthy or, most importantly, replace the health value of whole foods. Do not take a multivitamin or any other vitamin and ever consider that as replacement for healthy whole foods.


  1. Brasky, T. M., et al. (2017). “Long-Term, Supplemental, One-Carbon Metabolism-Related Vitamin B Use in Relation to Lung Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort.” J Clin Oncol: JCO2017727735.

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