Nori (Laver): Nutrients, What Research Shows and Safety

Nori is the dark red-purple seaweed called laver, from the genus Pyropia (formerly Porphyra), a red alga. It is pressed into thin dried sheets and used around sushi and rice balls, or crumbled over food. [2] People eat it for flavor, and some plant-based eaters ask whether it can supply vitamin B12. This page separates the whole food from snacks and supplements, and says what research does and does not show.

Read this first

• Iodine: nori is a lower-iodine seaweed than kombu or wakame, but it is not iodine-free. One lab survey found about 16 micrograms (mcg) per gram in nori, against more than 8,000 mcg per gram in a kelp salt substitute. [5] A Taiwan analysis found nori averaged about 37 mg per kg, wakame about 140 and kombu about 2,523. [6] Seasoned snack sheets are a separate story: see seaweed snacks.
• Vitamin B12: do not count on nori as your B12 source. Some purple laver contains true B12, but the human evidence is small and mixed, and health bodies tell vegans to use fortified foods or a supplement. [2] [3] [4] [8] [9]
• Thyroid disease, pregnancy, young children: iodine from seaweed can matter. Ask your own clinician; we do not tell anyone to eat or avoid nori for a thyroid condition. [11]
• Allergy emergency: for trouble breathing or swelling of the face or throat, call 911 (or your local emergency number). Proper evidence on nori allergy was not found in the sources we read.
• Evidence in one line: one small 4-week trial in 30 vegetarians found roasted nori improved blood B12 markers; no trial shows nori treats or prevents disease. [3]

What is in it (USDA values)

The USDA item below is "Seaweed, laver, raw" (FoodData Central 168458, SR Legacy). [1] This is wet laver as it comes out of the sea. It is not a dried sushi sheet or a roasted snack, so dried sheets weigh much less per sheet and hold much more per gram. The serving column is the USDA household portion of 10 sheets, 26 g. [1]

% Daily Value uses the FDA 2016 Daily Values; serving figures are the 100 g values multiplied by 0.26. Values vary with species, harvest place and processing. [1] USDA lists no iodine for this food. USDA's B12 value of 0 does not prove nori lacks B12, because the USDA method does not tell true B12 from look-alike molecules; other measurements are below. [2]

For dried purple laver, a review of Japanese food-table data and other surveys gave 77.6 mcg B12 per 100 g dry weight, with other reports from about 12 to 134 mcg per 100 g depending on species and product. It also gave about 10.7 mg of iron and 1.19 g of n-3 fatty acids per 100 g of dried laver. [2] Those are dry-weight numbers and cannot be compared with the wet USDA row. Dried sheets are light: the review says one sheet is about 0.3 g. [2]

What research says

Eaten as food vs taken as supplement. The trial above used roasted nori sheets as food. We did not read any trial of nori extracts or nori tablets. The cooking-style Welsh laverbread (a laver puree) is not covered by the sources we read, so we say nothing about it.

How much is a normal serving

The USDA household portion for raw laver is 10 sheets (26 g), or 2 tablespoons (10 g). [1] That is information, not a prescription. For dried sushi nori, the trial used 5 g and 8 g a day for 4 weeks, which is a research dose, not advice. [3] The sources we read give no official nori serving from a health body.

Safety, allergy and medicines

• Iodine and thyroid: seaweed can bring too little or too much iodine to the thyroid. The Teas survey concluded some Asian seaweed dishes might exceed the adult upper intake limit of 1,100 mcg a day. [5] Nori is lower than kombu or wakame in that survey and in the Taiwan analysis, but "nori wrappers" in a Hong Kong test (2022) reached 34,600 mcg per 100 g in one rice-ball product, giving 450 mcg in a 1.3 g serving. [6] [10] Levels differ between products, so label and species matter: a Norwegian survey of 96 seaweed products found iodine content high and labeling of species and iodine often inadequate. [7] NHS says high iodine doses over a long time can change how the thyroid works. [11] If you have thyroid disease, are pregnant or breastfeeding, or feed young children, ask your clinician. See seaweed iodine and thyroid.
• B12 trust: do not stop a prescribed B12 supplement or fortified foods because you eat nori. NHS lists a vegan diet without B12 supplements or fortified foods as a deficiency risk. [9]
• Metals: the Hong Kong test found cadmium and inorganic arsenic in all 27 ready-to-eat seaweed samples (18 snacks, 8 nori wrappers, 1 shredded), all within the limits it applied. [10] See heavy metals in foods.
• Warfarin and kidney disease: the Hong Kong Consumer Council advised people with chronic kidney disease or on warfarin to consult a doctor or dietitian before eating seaweed. [10] USDA lists a small amount of vitamin K in wet laver (4 mcg per 100 g). [1] Keep intake steady and tell your care team.
• Allergy: proper evidence on seaweed allergy was not found in the sources we read. Seasoned sheets may carry soy, wheat, fish or sesame in the ingredients; read the label.

Choosing, storing and food safety

• Check the pack for species, iodine and sodium information. The Hong Kong Council asked makers to list iodine on labels, and found some label values did not match test values. [10]
• Proper evidence on storage times was not found in the sources we read.
• Plain sheets are different from seasoned snacks; see the snack page below.

Related pages

• Seaweed snacks (roasted nori)
• Seaweed and vitamin B12 claims checked
• Iodine in seaweed: how much by type
• Seaweed iodine and thyroid
• Vitamin B12 for vegetarians and vegans
• Wakame