Nori (Laver)

Food · Vegetables · Sea Vegetables

Connected to · 1

food source · 1

Vitamin B12
Dried nori contains real, active B12, and one review judges it the most suitable natural source currently available to vegetarians; but the amount varies widely with species and processing, so it cannot be the only source. What is measured in spirulina, by contrast, is mostly inactive look-alikes.
Mechanism · 2
Mechanism · Real B12, not a look-alike
Watanabe 1999 measured it two ways and found that dried nori contains a substantial amount of active B12, not the look-alikes in spirulina that the body cannot use. Plants do not make B12 themselves, and the B12 in nori is thought to come from bacteria associated with the alga.
Evidence · Containing it is not covering it
The amount can differ severalfold between species and between ways of drying and storing, and in some samples the B12 breaks down into inactive look-alikes; the UK Vegan Society and other bodies still list seaweeds, nori included, as unreliable B12 sources. A small open-label trial in 2024, with 30 vegetarians over 4 weeks, found that eating roasted nori improved serum B12 and related markers. That is a positive signal, but it is one small, short trial that still needs repeating, and it is not enough to justify stopping a supplement. So nori is a bonus, not a plan.

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What is nori · a sheet of red seaweed

EVIDENCEGUIDE 1

READ THE ORIGINAL

Nori is far lower in iodine than kelp, so it is a seaweed you can eat every day. It also contains real, active vitamin B12, which is rare in plant foods, but the amount is unreliable, so vegans cannot use it as their only source. Why its B12 is real but unreliable is explained in the chapter on whether nori's B12 counts.

Nori is the dark-green, crisp, sea-scented sheet wrapped around sushi; onigiri wraps and seasoned nori snacks are the same thing. It is a red seaweed, a different class from kelp, which is a brown seaweed.

One more thing about it is often oversold: by dry weight its share of protein is striking, but a sheet weighs only a few grams.

Two dark olive-green roasted nori sheets, one tilted and one curled at the front edge. — A CLOSER LOOK
A large-looking sheet is paper-thin
These are roasted nori sheets; a large surface area does not mean a large weight is eaten.

Educational content, not medical advice — consult a clinician.

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