Nori: Its Potential as a Plant Source of B12

I just read an interesting paper from March 2011 (sent my way by Dave of It was a cross-sectional study on semi-vegan, Buddhist nuns from Korea. The study was done by German researchers studying how the nuns’ B12, folate, and iron intakes were affecting their blood cell size (1).

The nuns’ blood cells appeared fine, indicating that either they were getting plenty of vitamin B12 for the purposes of their blood cells, or that they were getting enough folate to mask a B12 deficiency. I should also point out that there are two types of B12 deficiency – one that causes blood problems (which can be masked by high intakes of folate) and one that causes nerve problems (that cannot be masked by high folate intakes).

For me, the more interesting part of the paper was how strongly the researchers suggested that nori (also known as laver) is a reliable source of vitamin B12.

The semi-vegan Buddhists ate some dairy, but it was not very much according to their diet diaries (only 21 grams per day on average). If you assume they were drinking milk, 21 grams would be only about .1 µg of B12 per day. That is not enough to keep vitamin B12 levels at the 360 pmol/l that they averaged, indicating they either were eating more animal products than reported or were getting their B12 elsewhere, such as from nori.

The nuns ate 1.3 g of nori per day. According to previous studies, nori contains anywhere from about 1.5 to 20 µg of B12 analogue per 30 g. That would mean 1.3 g of nori would contain .05 to .6 µg. If we generously assume the nori had the very highest amount of B12 and add the .6 to the .1 µg from dairy products, you get .7 µg of B12 per day in the best case scenario. That still does not seem to be enough to explain such high B12 levels.

However, the semi-vegans did eat other sea vegetables and many sea vegetables are known to have B12 analogues. Generally, blood B12 levels of people who eat significant amounts of sea vegetables cannot be considered reliable, because the testing methods cannot discern between active and inactive B12 analogues.

There have been quite a few studies measuring the vitamin B12 content of nori. But only one has actually tested the seaweeds’ effect on methylmalonic acid (MMA) levels. MMA is the only marker that can determine true vitamin B12 activity as it is not impacted by high folate intakes. When there is not enough active B12 in the blood, MMA levels rise. The one study on nori that measured nori’s effects on MMA levels found that it increased MMA levels, though the increase was statistically significant for only dried nori and not from raw nori. This means that dried nori had anti-B12 activity, while the raw nori did not improve nor harm B12 status. Most nori eaten in the U.S. is dried.

This current study on semi-vegan Buddhist nuns in Korea could have at least partially solved this whole question of B12 sufficiency by testing MMA levels. Although it would not necessarily have meant that the nuns’ were getting most of their vitamin B12 from nori, healthy MMA levels would have at least indicated if most of the B12 in their blood was active.

The study that really needs to be done is to take some willing vegan participants in the Western world and have them avoid all B12 supplementation until their MMA levels increase above normal. Then feed them nori purchased in stores in the U.S. and see what it does to their MMA levels and how much is needed. If their MMA levels improve, then the same study should be performed a few different times on different people and with different batches of nori. Three successful studies like this would satisfy me that nori is a reliable source of vitamin B12 for vegans. Until these studies are done, choosing nori instead of B12-fortified foods or supplements could result in vegans harming themselves.

In countries where vitamin B12 fortification or supplements are not readily available, it makes perfect sense that researchers would hope that B12 would be in an available food such as nori. And, while I am quite skeptical of its reliability, I certainly hope nori turns out to be a reliable source of vitamin B12.

While I would be very happy to see a new source of vitamin B12 for vegans, especially in developing countries, this would not therefore prove that a vegan diet is “natural”. That question is answered by the fossil evidence as to whether Homo sapiens ate animal products throughout our evolution, and not whether plants could theoretically provide all the nutrients necessary for sustaining human life.

Humans have always had a rich, vegan source of vitamin B12 close by – our feces. Human feces contain much active vitamin B12. However, that does not mean that anything that gets contaminated with the bacteria from human feces is, therefore, also a rich source of vitamin B12. I have yet to see convincing data that human feces contamination on food, in water, or just in the soil can produce enough vitamin B12 to sustain humans, much less keep their homocysteine at a healthy level.


1. Lee Y, Krawinkel M. The nutritional status of iron, folate, and vitamin B-12 of Buddhist vegetarians. Asia Pac J Clin Nutr. 2011;20(1):42-9. Link

10 Responses to “Nori: Its Potential as a Plant Source of B12”

  1. Ellie Says:

    I have a follow up question on B12 – Ginny states somewhere on her site that the methylcobalamin form of B12 does not provide enough of the vitamin when taken in the doses/RDA recommended. Those doses are specifically for cyanocobalamin B12. Are there any studies or recommendations for methylcobalamin B12 or can you give me any more details on the differences between the two?
    Thanks so much,

  2. Jack Norris RD Says:


    Methyl- is usually recommended in 1,000 µg per day. More info:

  3. Gabriel Says:

    One of the issues with nori (and probably with most seaweeds) is that there is a high likelihood that the sheets contain fish and crustacean parts that get trapped in nets due to the way it is harvested. Personally I only use hand-harvested nori to minimize the likelihood of these animals getting killed and processed into the sheets. It does make me wonder if the B12 in nori is actually from sea creatures that were processed into the sheets. It would be interesting to see the difference in B12 content between hand-harvested nori and conventionally harvested nori.

  4. Duncan Says:

    Hi Jack
    I live in Korea, am mostly vegan and am interested in this study for obvious reasons. I have heard anecdotally about the B12 content in various korean foods such as Kimchi and after reading your piece I did a quick scan and came up with this…

    Nothing conclusive but interesting conclusion.

    and this one..

    “Surprisingly, the results of preliminary studies of centenarian diets showed that vitamin B12 status of Korean centenarians, who have consumed vegetable-based diets throughout their lives, was higher than our expectations. Therefore, we traced the unknown natural sources of vitamin B12 in traditional Korean foods”..

    But i guess take-home message would be unless you are truly eating like an older generation Korean don’t give up the supplements just yet..

  5. Jack Norris RD Says:


    I’m excited that you found the abstract to the Kwak et al. 2008 article. I had not been able to locate it on PubMed. Maybe it should have occurred to me to do a Google search. Unfortunately, they used a Lactobacillus delbruecki assay which has not been shown to distinguish between active and inactive B12.

  6. VeganMoFo 9: Vegan news you can use (B12!) and the weekly-round up (10/9/11) Says:

    […] Nori: Its Potential as a Plant Source of B12 […]

  7. Ales Says:

    Hi Jack,

    I just found that in recent years, blood test for B12 has become more accurate, because the test only measures biologically active B12. Does this mean that B12 analogues does not increase B12 values in blood tests?

    Section: Considerations:
    “The blood test for levels of vitamin B12 has become much more accurate within the past few years. Now, there are fewer false-normal results, because the test only measures biologically active B12.”

  8. Jack Norris RD Says:


    I don’t know. I haven’t heard this before and I’m not sure why that would be the case (though I can imagine how it might be). At this point, I’m skeptical though it’s possible.

  9. dimqua Says:

    Did you see this review, Jack?

  10. Jack Norris RD Says:


    Yes, and I just posted on it:

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