Hijiki: Nutrients, What Research Shows and Safety

Hijiki (Sargassum fusiforme, also called Hizikia fusiforme) is a brown seaweed from the coasts of East Asia. It is sold dried as thin black strands, soaked and cooked, often with vegetables and fried bean curd in Japanese home cooking. [8] It is the one common sea vegetable that several governments have told people to avoid, because it holds much more inorganic arsenic than other seaweeds. This page reports what each agency said and where they differ, and separates the food from supplements and hype.

Read this first

• Inorganic arsenic is the lead safety story. The UK Food Standards Agency (FSA), the Canadian Food Inspection Agency (CFIA), the Hong Kong Centre for Food Safety (CFS) and Food Standards Australia New Zealand (FSANZ) have each advised people to avoid hijiki. [1] [4] [5] [6] Japan's health ministry took a different line in 2004: usual intake is low, so the risk does not rise in a balanced diet unless a very large amount is eaten. [7] See the table below, and the guide on heavy metals in seaweed and the hijiki advice.
• Inorganic arsenic is the more toxic form. It is linked to skin, bladder and lung cancers in people. [11] Most arsenic in other seaweeds is mostly organic, and the UK survey found none of the inorganic kind above its detection limit in the other four seaweeds it tested (including arame). [3]
• Hijiki also carries a lot of iodine (a Korean survey averaged about 527 mg per kg dry weight). Too much iodine can disturb the thyroid. [13] [16]
• Pregnancy, children and thyroid disease: a Japanese study found that frequent hijiki eaters, pregnant women and children among them, had higher inorganic arsenic intakes. [10] Ask your clinician about hijiki and thyroid disease or pregnancy.
• Allergy: seaweed allergy is rare, but for trouble breathing or swelling of the face or throat, call 911 (or your local emergency number). [19]
• Evidence in one line: the arsenic findings are measurements and risk calculations, not cases of poisoning; the health benefit claims for hijiki are mostly laboratory findings.

What is in it (no USDA entry)

No USDA entry for this food: USDA FoodData Central (SR Legacy) has no listing for hijiki, so we do not show a USDA nutrient table. We did not find a full nutrient table for hijiki in the sources we read, and we do not invent numbers. What the sources did measure is below. These are dried seaweed unless stated, and values vary a lot with harvest place, season and processing.

For comparison, sea tangle (a kombu-type kelp) averaged 2,432 mg iodine per kg dry weight in the same Korean survey, and the same survey found hijiki iodine rose to its highest in the February and March harvest season. [13] The 2004 Thyroid study found nori about 16 mcg per gram. [17]

Plant compounds: we did not read a human study on hijiki's plant compounds. Extracts studied in laboratories (for example antioxidant peptides) are lab findings only and say nothing about eating hijiki.

What research says

Eaten as food versus taken as supplement: we read no trial of hijiki capsules or extracts. A review of seaweed risks and benefits says human trials are still needed. [21]

How much is a normal serving

There is no official serving size for hijiki in the sources we read, and we give no dose advice. For information only: a Japanese study estimated about 6.5 g a day on average for cooked hijiki households, based on serving size and how often it is eaten (two to three times a month in most households). [8] The Korean national survey estimated an average of 0.09 g of hijiki a day per person. [13] Official advice from the UK, Canada, Hong Kong and Australia is to avoid it, not to limit it. [1] [4] [5] [6]

Safety, allergy and medicines

What each agency said (as read):

The Japanese position was reported in a short excerpt of a Tokyo Metropolitan Government FAQ; we could not open the ministry's own document. [7] Later research partly challenges "low intake": hijiki is the main algae source of inorganic arsenic in the Japanese diet [9], and frequent eaters have higher intakes. [10]

Other points:

• Preparation: in a laboratory study, heating hijiki at 90 °C for 5 minutes cut arsenic content by roughly 33 to 80%, and a salt-water soak reduced it further. [12] That is a lab result on whole plants; it does not make hijiki "safe" by the agencies' wording.


• Iodine: the adult upper level is 1,100 mcg a day in the US and 600 mcg in the EU (EFSA), as quoted in the sources we read. [17] [13] In the Korean assessment, hijiki consumers could exceed the EFSA level. [13] NHS says taking high doses of iodine for long periods could change how the thyroid works. [18]


• Cadmium, lead, mercury: an EFSA 2023 report found cadmium exposure from seaweed within the range of whole-diet estimates and inorganic arsenic and lead about 10 to 30% of whole-diet estimates for adult seaweed eaters. [15] It did not break out hijiki in the abstract we read.


• Other arsenic forms: EFSA 2024 judged arsenobetaine and a common arsenosugar unlikely to raise a health concern at current exposures. [20]


• Allergy: seaweed allergy is rare. Anaphylaxis signs include trouble breathing, throat swelling and shock; call 911 right away and use prescribed epinephrine. [19]


• Medicines, vitamin K, kidney disease, sodium: we did not find hijiki-specific figures in the sources we read. See seaweed, medicines and health conditions.

Choosing, storing and food safety

• Dried hijiki and its cooked dishes are the forms discussed above; the arsenic findings apply to hijiki specifically, not to arame, nori, kombu or wakame. [3] [5]
• Hong Kong's CFS advises checking labels on prepackaged foods for hijiki. [5]
• We did not read a source with storage advice for hijiki. See how to buy, prepare and store seaweed.

Related pages

• Heavy metals in seaweed: arsenic, cadmium and the hijiki advice
• Arame
• Iodine in seaweed: how much by type
• Seaweed in pregnancy and breastfeeding
• Heavy metals and contaminants in foods
• Seaweed, iodine and thyroid