Those who choose to follow a vegan diet, need to ensure an adequate source of B12. Usually this means a supplement. However, many people rely on seaweed as a source of B12 as they have heard it is a good source, specifically nori.
Nori, is the seaweed that is commonly used to make sushi (or nori) rolls that have been very popular in our culture. Some studies have found that nori has a significant amount of B12 and the researchers have even states that nori is a, “most excellent source of vitamin B12 among edible seaweeds, especially for strict vegetarians.”
Watanabe F, Takenaka S, Katsura H, Masumder SA, Abe K, Tamura Y, Nakano Y. Dried green and purple lavers (Nori) contain substantial amounts of biologically active vitamin B(12) but less of dietary iodine relative to other edible seaweeds. J Agric Food Chem. 1999 Jun;47(6):2341-3.
One study found that the B12 in the nori comes from a symbiotic relationship with the bacteria that live on the nori.
Croft MT, Lawrence AD, Raux-Deery E, Warren MJ, Smith AG. Algae acquire vitamin B12 through a symbiotic relationship with bacteria. Nature. 2005 Nov 3;438(7064):90-3.
Other information, as this article implies, is that the B12 in nori may be coming from tiny crustacean that are caught and ground up in the production of the Nori, which of course, would mean it is not technically vegan nor would it be an acceptable vegan solution to the B12 issue. (NOTE: Amphidods are tiny shrimp like crustaceans)
Food Additives and Contaminants, Volume 24, Number 9, September 2007 , pp. 917-922(6) Allergenicity and allergens of amphipods found in nori (dried laver)
So, these issues raise several questions and I turned to my colleague Jack Norris, RD who wrote an excellent article on B12 for vegans, for his responses.
1) Do you think the B12 is coming from crustaceans or from a "symbiotic relationship with
I don't know. It could possibly be both.
2) Does nori contain active B12 and if so, how much.
According to Jack Norris, RD, "A portion of its B12 analogue, especially in raw (vs. dried) nori, probably active. "
3) Has this amount be quantified?
"Yamada et. al. tried to quantify it. They determined that dried nori had 1.5 mcg of active B12 and raw nori had 2.7 mcg (per 30 g of nori). "But the more important question is whether it lowers MMA levels (which might be a function of how much active B12 compared to inactive B12 it has). A food could have a great deal of active B12, but unless it lowers MMA levels, it's not going to do much to help prevent B12 deficiency.
4) Can Nori be relied on as a dependable source of B12 for a vegan?
I would never recommend a food as a source of vitamin B12 until it is consistently shown to reduce methylmalonic acid (MMA) levels. As I show at the link you list below, the one time nori was tested, the dried nori *increased* MMA levels, and the raw nori also increased levels but not to a statistically significant degree. Based on that, nori should not be recommended to prevent B12 deficiency.
Well, there you have it.
While nori may indeed contain B12, and soe of it in its active form, without further evidence, it should not be relied upon as dependable source of B12 for a vegan.
And in fact, it may not even be vegan, though some companies are now selling "fish-free" nori.