Vitamin B12 in Nori

Summary A review paper by the Watanabe group suggests that vegans can rely on nori for vitamin B12. I strongly advise against this.

There is a group of researchers in Japan who regularly publish papers in scientific journals about plant sources of vitamin B12. Fumio Watanabe is often the lead researcher, so I refer to them as the “Watanabe group.”

Some of their papers analyze the B12 in foods such as mushrooms, algae, and black tea, while other papers are just review articles of previous research. The latter is the case with their latest paper, Vitamin B12-containing Plant Food Sources for Vegetarians, published in the May 5, 2014 issue of Nutrients (1). A free version can be obtained at the link.

When the Watanabe group analyzes a food for B12, they often find molecules that they believe to be the vitamin. But a complication with simply finding B12 in food is that the food might also contain inactive B12 analogues that interfere with active B12. The Watanabe group is well aware of this and often analyzes the food for some of the typical inactive B12 analogues. Sometimes they feed the food to rats to see if it lowers the rats’ methylmalonic acid (MMA) levels, the prime indicator of B12 activity. Based on how much active B12 and inactive analogues they find, and any results with rats, they make recommendations as to whether a food can provide B12 for vegans.

In their latest review, based on the results of their various experiments combined with a study in which six vegan children stayed healthy eating large amounts of seaweed (my analysis here), they suggest that nori is a “suitable” source of B12 for vegans.

The biggest flaw in this theory is that there is a study that tested raw and dried nori using the gold standard of lowering MMA levels in humans (2), and although the authors of this study were optimistic about raw nori, the fact was that both dried and raw nori reduced B12 status in their subjects.

I often hear from people who say they have been vegan for some time, have not supplemented with B12, and are not B12 deficient. They take this to mean that vegans don’t need a supplemental source of B12. In most cases they do not know whether, in fact, they are B12 deficient or not, because they haven’t been appropriately tested for deficiency. And once you go vegan without a source of B12, you never know when deficiency symptoms might kick in – someone can be fine for years and then one day they start to feel tingling in their fingers or toes or they become severely fatigued. You don’t want to end up like any of the vegans listed in the Individual Cases of Deficiency.

There is also the problem of subclinical B12 deficiency where someone doesn’t feel any symptoms but has mild deficiency for years that can possibly develop into dementia or a stroke. As the Watanabe group says in their latest paper:

“However, Vitamin B12 deficiency may go undetected in vegetarians because their diets are rich in folic acid, which may mask vitamin B12 deficiency until severe health problems occur. Vitamin B12 deficiency contributes to the development of hyperhomocysteinemia, which is recognized as a risk factor for atherothrombotic and neuropsychiatric disorders, thereby negating the beneficial health effects of a vegetarian lifestyle.”

This does not mean that vegans need to get tested for B12 deficiency. On the contrary, I don’t see any need for that unless you decide not to supplement with B12 according to the recommendations here or you are supplementing but experiencing symptoms of B12 deficiency.

Whenever I post about B12, it is inevitable that someone, I suspect an internet troll in many cases, will pipe in to say that cyanocobalamin is not a good source of B12 but that methylcobalamin is. Except in very rare cases, this is not true (see Methylcobalamin & Adenosylcobalamin for more information). If you decide to rely on methylcobalamin, I recommend at least 1,000 µg per day.

If this post interested you, you might also want to read my August 2013 post about the Watanabe group, B12 in Plants and Algae Update.

In conclusion, there is no new evidence to suggest that nori is a reliable source of B12 for vegans and I advise against relying on it.


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1. Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B12-containing plant food sources for vegetarians. Nutrients. 2014 May 5;6(5):1861-73. | link

2. Yamada K, Yamada Y, Fukuda M, Yamada S. Bioavailability of dried asakusanori (porphyra tenera) as a source of Cobalamin (Vitamin B12). Int J Vitam Nutr Res. 1999 Nov;69(6):412-8. | link

38 Responses to “Vitamin B12 in Nori”

  1. Michael Greger, M.D. Says:

    Thank you for your astute work on B12 as always. Particularly appreciated your note about cyano vs. methyl- forms. Keep up the great work!

  2. Jack Norris RD Says:

    Thank you for your kind words, Dr. Greger!

  3. Grace Says:

    Thank you so much for your detailed work on b12, and for all the info you give here and on This is my favourite nutrition blog. As a keen student of nutrition, I’ve learned so much from reading your stuff, and my diet and health are better for it.

  4. Joel Says:

    Hi Jack,
    Your note at the end of this post is concerning and confusing to me. I could have sworn I began taking Deva’s Vegan B12 as a result of a recommendation in your blog, although I can’t find it now. Anyway, that’s methyl-. But you are saying that it would be better for the average person (I’m 64 and male by the way) to be taking cyano-? Oy. So … where do I find that?
    Thank you. I rely on your advice — Joel

  5. Jack Norris RD Says:

    Hi Joel,

    I’m not sure what you saw, and I can see how it could get confusing (perhaps I had suggested Deva as a decent source of vegan vitamins?), but I have been very consistent in saying that methylcobalamin is only needed in rare case. If you take 1,000 µg of methylcobalamin per day, it should work as well as cyanocobalamin.

  6. Joel Says:

    Hi again Jack,
    Well, I just used the Pangea link at your site and searched for B12, but only methyl- came up (the Deva I’m already using). Any suggestions for cyano- sources?
    Thanks again, and Happy Labor Day ‘-) — Joel

  7. Jack Norris RD Says:


    You should be able to get cyanocobalamin at any grocery or drug store, it’s the most common form of B12 by far.

  8. Joel Says:

    Okeedoke. Thanks — Joel

  9. Andrea Says:

    What is the point of researching B12 levels in plants when all plants are low in B12 and B3?

    The big question is how do wild animals have high levels of B3 and B12 in their tissues while on a diet extremely low in B3 and B12?

  10. Dan Says:

    It is easy to take B12 supplements: they are dirt cheap and reliable for raising B12 levels in vegans. People fear chemicals (“chemophobia”) but don’t realize that food contains thousands of chemicals.

  11. JT Says:

    Many of us do not absorb B12 from supplements and need regular shots. Every vegan should get tested, and if supplements are not raising your levels, then research pernicious anemia. More and more of us are discovering this problem. Depression is another horrific symptom of possible B12 deficiency.
    I didn’t worry about B12 for years, but now I know better. This can be a very dangerous health issue.

  12. Jack Norris RD Says:


    I agree that B12 can be a dangerous health issue, but there is no reason why someone should be tested only because they are vegan. If someone can’t absorb B12 from supplements, then they can’t absorb them from animal products (it’s actually a lot easier to absorb them from supplements). So vegan who take supplements have an advantage over meat-eaters. Research has also shown that taking 2,000 µg per day is actually more effective than injections in people who have pernicious anemia:

  13. Dan Says:

    I had a very high B12 level on a meat-eater’s diet more than 2 years ago. I have not checked my B12 on supplements – I just assume they are working (100-250 µg per day). Should I check my B12 count? (I assume if I can absorb it from meat and have such a great level then surely I can absorb it from an isolated synthetic in a supplement).

  14. Jack Norris RD Says:


    I find your logic to be very good and would not see why you would need to get your B12 checked.

  15. Mikko Says:


    It’s no mystery. B12 is produced by bacteria in the soil, not by animal cells. Wild herbivore animals get a lot of B12 as their plant food comes with some soil on it. Carnivores eat the meat of the herbivores and get B12 from soil indirectly that way. Some animals can also absorb B12 made by bacteria in their guts. There’s also soil bacteria with B12 in untreated water in the lakes, streams etc.

    Human beings would probably do fine if we could still drink our water untreated from the nearest creek, or eat some not-so-well washed potatoes straight out of the ground.

  16. Jack Norris RD Says:


    B12 is produced by bacteria living in the digestive tracts of animals.

    It makes sense that there would be B12-producing bacteria in feces-contaminated soil and possibly actual B12 in that soil. But the idea that all soil contains a significant amount of B12 such that if we didn’t sanitize our food and water we could get ample B12 from it is lacking evidence as far as I can tell. Here is something I wrote on the subject that you might find interesting:

  17. Brandon Becker Says:

    Andrea says above that plants are low in B3. That’s not true. See the chart on this page:

    When calculating my daily diet, I never have a problem meeting the RDA for B3.

    Regarding B12, if there was enough evidence that I could rely on nori/laver seaweed for B12 and not have to take supplements, I would. I already eat seaweed snacks to ensure iodine and also because they taste good and are nutritious in other ways. It’s not about fear of chemicals (though we should be skeptical of anything synthetic based on the precautionary principle) but rather about not wanting to waste money on pills and have to remember to take them.

  18. Dan Says:

    We are immersed in a world of synthetic compounds. That doesn’t by itself bother me. If you’ve ever eaten food from the grocery store/supermarket (even the organic stuff), you will have consumed synthetic compounds. They are in the packaging, and of course in the air, water and soil, whereby they get into plants. Most medications are synthetic.

    I am just making this point because people seem to object to cyanocobalamin because it’s synthetic. Anything made by a person is synthetic. One need only open one’s eyes to see how that fact is rarely relevant to good health (a few controversial compounds aside). There are many naturally derived compounds that could kill a person if ingested even in infinitesimal amounts (such as phyllotoxins in certain mushrooms)

  19. Brandon Becker Says:

    The question is whether something is toxic or not. Many chemicals created by humans, meaning synthetics, are toxic. I assume all synthetics are harmful based on the precautionary principle unless they are shown not to be. Note that I’m not saying that anything natural is harmless – there are plenty of compounds found in nature that can kill humans like you mentioned with certain mushrooms. As I said, the question is whether something is toxic or not. Cyanocobalamin at the recommended amounts has shown to be safe, because your liver filters out the cyanide. I’m going to keep taking it until there is enough evidence that I can rely on nori/laver seaweed for B12.

  20. Brandon Becker Says:

    I found a paper from 1990 discussing natural versus synthetic chemicals:

    “We conclude that natural and synthetic chemicals are equally likely to be positive in animal cancer tests.”

    So let’s assume everything is unsafe unless proven safe rather than assuming safety without evidence.

  21. Andrea Says:


    Nice assumptions.


    Which foods are you talking about as sufficient sources of B3?

    Mushrooms, sunflower seeds and other plant foods somewhat rich in B3 are a RARITY! They dont count to fulfill our nutritional requirements.

    Animal flesh food names don’t count as sufficient sources of B3 since the flesh rich in B3 came from animals consuming a diet low in B3. Are you able to solve the riddle of how animals are able to have high levels of B3 in their flesh while consuming a diet low in B3?

  22. Brandon Becker Says:

    Why do you call those foods a “rarity”? I eat them all the time and they are easily found in grocery stores where I live in NC. They certainly count to fulfill our nutritional requirements. There’s no reason anyone eating a variety of plant foods and getting enough calories should worry about niacin.

  23. Brandon Becker Says:

    The body can also make niacin from the amino acid tryptophan, also easily found in plant foods:

  24. rick Says:

    From on b12 recommendations: “Amounts much larger than these are considered safe, but it’s probably best not to take more than twice the recommended amounts.” If high doses are considered safe, then would you please explain why t’s probably best not to take more than twice the recommended amounts?

    Also as I recall from either one of your posts or, you referenced a study showing b12 helpful in treating depression, but ONLY in the methyl form.


  25. Jack Norris RD Says:


    This sort of statement is a guess. To date, there have been few problems associated with high intakes of vitamin B12. But there have not actually been long-term clinical trials testing various amount of vitamin B12. So, we don’t have much reason to believe that large amounts of vitamin B12 are harmful, but why risk it?

  26. Toyo Says:

    1000ug of B12 is a massive dose, hundreds of times greater than the RDA. What is the rationale for megadosing like this?

  27. Toyo Says:

    I now see the rationale for recommending the high doses:

    “Some researchers question whether these non-cyanocobalamin supplements are stable in their oral form. For this reason, much larger amounts are typically used with the hope that at least some is absorbed intact. ”

  28. Jossi Says:

    As I know, you can only absorb about 1.6 microgram per intake on the active way using the intrinsic factor. But about 1% will get absorbed passively via diffusion.
    That means you will absorb 11.6 microgram per 1000 microgram pill.
    That’ll either help to cure an existing b12-deficiency (taken once or twice a day) or prevent a deficiency if taken twice a week (some prefer that).

    I cured my mild b12-deficiency with 2000 microgram methylcobalamin a day within a month and am now down to 2000-3000 microgram a week to keep it stable.
    I was a bit insecure about cyanocobalamin since some people said it might have some side effects if you take such a high amount, so I decided to go for methylcobalamin. This information might well be wrong, but anyway, methylcobalamin worked for me and it isn’t that expensive.

  29. TC Says:


    Great article!

    What about b12 from creek water or un-treated or unfiltered water from natural sources?

    I’ve heard on the intertube that natural water sources and soil are the places where people were ‘meant’ to get vitamin b12 from. I saw your early post about soil not having enough b12 but how about natural water sources? If they do, is it because the b12 dissolves in the water source from the ground it’s running through or is it from the bacteria?

    If animals are able to get their vitamin b12 from bacteria, and that’s they only source animals get it from, then why can’t we get it from just eating the same bacteria? Why can’t we get it from probiotics like what’s found in live yeast and sauerkraut?

  30. Jack Norris RD Says:


    Carnivorous animals get B12 from eating other animals. Here is a link about herbivorous animals:

    Fermented foods:

  31. Katie Says:

    Hi Jack. I’ve been vegetarian for about 15 years, and I eat eggs several times a week and dairy every day. I also supplement with B12-fortified nutritional yeast and occasionally with the MegaFood Blood Builder (which also appears to derive its B12 from nutritional yeast).

    My understanding is that the yeast itself cannot produce the B12 and that it is supplemented with B12 from a cyanobacteria. Is this correct? Is the difference in how the body absorbs the B12 based on which bacteria produces it? If so, how would you know which bacteria was used to fortify the nutritional yeast? Contact the manufacturers? Or is it standard practice to use the type that creates the readily-absorbed form of the nutrient?

  32. Jack Norris RD Says:


    > and that it is supplemented with B12 from a cyanobacteria.

    It’s produced from bacteria, but I’m not sure about the “cyano” part. My sense is that nutritional yeast companies just buy crystallized B12 from a vitamin producer and sprinkle it onto the nutritional yeast–they probably don’t have anything to do with the actual bacteria that produce the B12. The form of B12 they use is almost certainly cyanocobalamin, which is the most stable form and is absorbed well.

  33. Katie Says:

    Also, if the form from nutritional yeast is not well absorbed by the body, which brands would you recommend? Would the standard bottle of B12 pills from the grocery store work? I would just want to make sure it’s from a vegetarian source!

  34. Katie Says:

    Wonderful, thanks for taking the time to write back!

  35. Ari Says:

    hi dr jack norris!! i supplement b12 daily with methylcobalamin (had acne with cyanocobalamin form), so can i keep eating seaweed or it will still interfere in the actual b12 system? its my main source of iodine…is it safe?

  36. Jack Norris RD Says:


    Eating seaweed a few times a week is fine.

  37. Ari Says:

    Thank you dr. jack norris!!!

    could you please inform me if seaweed have any DHA or EPA? and if not, why? cause there is no DHA/EPA algae based supplements in my country (brazil), and it would be very expensive to import it.


  38. Jack Norris RD Says:


    Seaweed have very small amounts of EPA and DHA and you can’t get very much without concentrating it into pills. In other words, I’m sorry, but no. But you’d probably be fine sticking with making sure you get extra ALA.

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