Mozuku: Nutrients, What Research Shows and Safety

Mozuku is a soft, thin, slippery brown seaweed. The Okinawa kind is Cladosiphon okamuranus, a brown alga (class Phaeophyceae). It is eaten as a whole food, often served cold in a small dish with a vinegar-based dressing or in soups. The strands are coated in a slimy gel. That gel is rich in fucoidan, a sulfated sugar chain found in brown seaweeds. [7] Fucoidan is why mozuku is often called a health food. This page keeps the seaweed you eat apart from fucoidan extracts and supplements, and apart from hype.

Read this first

• No mozuku iodine figure found. We did not find a measured iodine amount for mozuku in the sources we read. Brown seaweeds can hold a lot of iodine: in one study kombu had 3,522 mcg per gram dry weight, wakame 27 and nori 5.0. [3] Mozuku was not tested in that study, so we cannot say where it falls. Too much iodine can upset the thyroid. [3] [5]
• Thyroid disease, pregnancy, breastfeeding and young children: ask your clinician or pharmacist before eating seaweed often. We do not tell anyone to eat or avoid mozuku for a thyroid problem. [3] [5]
• Blood thinners: the Memorial Sloan Kettering Cancer Center (MSK) page on fucoidan says it may add to the effect of anticoagulants such as warfarin and heparin. [6] That page is about fucoidan products; we did not find a source on whole mozuku and blood thinners. Ask your prescriber.
• Allergy: seaweed is not fish or shellfish. If you ever have trouble breathing or swelling of the face or throat after eating, call 911 (or your local emergency number).
• Evidence in one line: there is one small human trial of mozuku fucoidan (in a drink, not the whole seaweed), and bigger claims come from lab and animal work. [1] [2]

What is in it (USDA values)

No USDA entry for this food. USDA FoodData Central (SR Legacy) does not list mozuku, so we do not give a nutrient table. We also did not find a peer-reviewed composition table for mozuku (for example iodine, vitamin K or sodium) in the sources we read, and we will not guess numbers. Proper evidence not found in the sources we read.

What we did read:

• In growing mozuku, a lab study found that fucoidan sits in the cell wall and is more abundant in older thalli (the seaweed body), where it likely adds strength. [7]


• A lipid analysis of five Japanese seaweeds found mozuku's fats grouped with hijiki and laver, not with kombu or wakame. This is lab chemistry, with no health claim. [8]


• Mozuku is sold fresh in brine, salted, or dried, in different forms. Fresh, brined and dried products differ in water and sodium, so label values are not comparable. We did not find a source with measured values.

What research says

Eaten as food vs taken as an extract. The one human trial used a fucoidan extract in a drink. [1] A plate of mozuku is a different product: the amount of fucoidan in it was not measured in any source we read. Do not assume food gives the same effect. Fucoidan from different seaweeds also differs in structure, and that changes its activity. See Fucoidan.

How much is a normal serving

We did not find an official serving size for mozuku (no USDA portion, no Japanese or Australian guidance in the sources we read). We will not give one. Small side dishes are common in Okinawan meals, but that is a custom, not a rule. This is information, not a prescription. For how iodine adds up across seaweeds, see iodine in seaweed. Health Canada (2025) lists an iodine upper limit of 1,100 mcg a day for adults, and 200 to 600 mcg for children aged 1 to 13. [4] The European Food Safety Authority upper level is lower, 600 mcg a day for adults, as quoted in one study. [3]

Safety, allergy and medicines

• Iodine and the thyroid: excess iodine from seaweed has been linked to hyperthyroidism, thyroid inflammation and goiter, and children and pregnant people may be more vulnerable. [3] The American Thyroid Association (statement 2013, page updated 2024) advises against iodine and kelp supplements above 500 mcg a day. [5] That statement is about supplements, not about mozuku. Boiling cut iodine in the kombu studied by up to 99% after 15 minutes. [3] We do not know if that holds for mozuku.
• Arsenic and metals: most seaweeds contain mostly organic arsenic (arsenosugars), which the authors of one paper call "less toxic or for which the toxicity is not known"; hijiki is singled out for inorganic arsenic. [3] We did not find arsenic or cadmium results for mozuku. Boiling cut arsenic by 43 to 50% in the seaweeds tested. [3] See heavy metals in foods.
• Blood thinners and surgery: MSK says fucoidan may have additive effects with anticoagulants. [6] Seaweed fucoidan has shown anticoagulant-like activity in the lab; see the fucoidan page. Tell your care team if you take warfarin or similar medicines.
• Pregnancy and breastfeeding: Health Canada lists upper limits of 1,100 mcg a day for pregnancy and breastfeeding at ages 19 to 30. [4] Ask your clinician about regular seaweed.
• Kidney disease, diabetes, sodium: we did not find sourced mozuku values for potassium, sodium or sugar-lowering effects, so we make no claim. Fresh mozuku is often sold in brine, which we could not source; read the label.
• Allergy: seaweed allergy is rare, and we did not read a mozuku case. Seasoned or dressed products may contain soy, wheat or fish, so read labels. See food allergy basics.
• Safe handling: fresh mozuku is a raw ready-to-eat food. We did not find a mozuku-specific food-safety source. General fresh-food rules apply.
• Whole-body claims: mozuku and COVID-19 and similar claims come from cell tests and reviews. [9] [10]

Choosing, storing and food safety

• Check the label for the form (fresh in brine, salted, dried) and for the sodium and added ingredients such as soy sauce or vinegar dressing.
• Keep fresh packs cold and follow the date on the pack; we did not find an official mozuku storage source.
• Rinsing brined mozuku before eating is a common kitchen step; we did not find a source on how much it changes iodine or sodium.

Related pages

• Fucoidan
• Iodine in seaweed: how much by type
• Heavy metals in seaweed and the hijiki advice
• Seaweed, iodine and the thyroid
• Kombu
• Seaweed medicines and health conditions