Nori, Kelp, Dulse, Spirulina & More: What Research Shows & What to Check.
Seaweed and algae come first as food. Explore each sea vegetable, microalga, extract and seaweed product: what is in it (measured by USDA where USDA has a value), what research in people has and has not found, a normal serving, and what to check before you eat it: too much iodine and thyroid disease, arsenic and cadmium (hijiki), vitamin K and warfarin, microcystins in blue-green algae supplements, sodium, pregnancy and children.
Search by seaweed or alga, benefit, body system, goal, symptom or lab test. Each result explains why it matches and how strong the evidence is.
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Laminaria japonica, Saccharina japonica
Iodine
Normal serving (USDA): 2 tbsp (1/8 cup), 10 g raw kelp
Kombu (kelp) as a food: why iodine comes first, USDA values, what studies found on thyroid, body fat and blood pressure, arsenic and cadmium, and who should check with a clinician.
Undaria pinnatifida
Normal serving (USDA): 2 tablespoons (1/8 cup), 10 g raw
Wakame as a food: iodine is the main safety point, USDA values for raw wakame, miso soup use, what research shows, arsenic and pregnancy notes, and the invasive-species background.
Eisenia bicyclis, Ecklonia bicyclis
Iodine
Normal serving (USDA): No official serving size found
Arame as a food: a mild brown seaweed from Japan. Its iodine, cadmium and arsenic as measured in a recent study, why it is not hijiki, and what research does and does not show.
Sargassum fusiforme, Hizikia fusiforme
Iodine
Normal serving (USDA): No official serving size found; Japanese study estimate for cooked hijiki about 6.5 g a day on average (information only)
Hijiki as a food: why government agencies disagree about its inorganic arsenic, what each one said, its high iodine, what research shows, and how it is cooked and chosen.
Cladosiphon okamuranus
Normal serving (USDA): No official serving found
Mozuku (Okinawa mozuku, Cladosiphon okamuranus) as a food: the slimy brown seaweed, its fucoidan, what small trials found, and iodine, arsenic and medicine cautions.
Pyropia spp., Porphyra spp.
ManganeseVitamin C
Normal serving (USDA): 10 sheets (26 g), raw laver
Nori (laver) as a food: iodine level, the vitamin B12 question (true versus inactive forms), USDA values for wet laver, snack sheet cautions, and what trials found.
Palmaria palmata
Iodine
Normal serving (USDA): No official serving found. The Arctic study authors calculated a maximum of 0.63 to 0.92 g dry weight a day for a 70 kg adult from iodine content
Dulse is a red seaweed from the North Atlantic. What research says about its iodine, protein and metals, who should be careful, and what is hype.
Eucheuma, Kappaphycus, Gracilaria
Iron
Normal serving (USDA): 0.25 cup rehydrated (25 g)
Sea moss (Eucheuma, Kappaphycus, Gracilaria) as a food: what the names mean, USDA values, iodine and metals first, and why "92 minerals" and other claims are not backed.
Ulva lactuca, Ulva spp.
Iodine
Normal serving (USDA): 1 g dried flakes (our arithmetic from per-100 g values; no official serving found)
Sea lettuce (Ulva) as a food: Japanese dried "aosa" nutrient values, high iodine per gram, pollutant questions, what small studies of extracts show, and who should be careful.
Caulerpa lentillifera
Normal serving (USDA): No official serving found
Sea grapes (umibudo, Caulerpa lentillifera) as a food: what farm analyses found, raw-food safety, salt and iodine gaps, and what lab and small human studies do and do not show.
Ulva and Monostroma spp.
Iodine
Normal serving (USDA): 1 g dried flakes (our arithmetic from per-100 g values; no official serving found)
Ao-nori (green laver) as a food: Japanese dried flake nutrient values, iodine per gram, why it is not nori for B12, salt, naming mix-ups, and who should ask a clinician first.
Aphanizomenon flos-aquae
Normal serving (USDA): No official serving; follow the product label
Blue-green algae (AFA) from Klamath Lake sold as capsules and powder: microcystin contamination, what human evidence exists, B12 claims, and cautions.
Dunaliella salina, Dunaliella bardawil
Normal serving (USDA): No official serving; no USDA entry
Dunaliella, a microalga rich in natural beta-carotene: the smokers and lung cancer warning, what small trials found, and how regulators treat it as a color and supplement.
Euglena gracilis
Normal serving (USDA): No official serving; no USDA entry
Euglena, a single-celled alga rich in paramylon beta-glucan: what Japanese and Korean trials found on colds and immunity, EU novel-food safety opinions, and how thin the human evidence is.
Nannochloropsis spp., Nannochloropsis oculata, Nannochloropsis gaditana, Nannochloropsis oceanica
Normal serving (USDA): No official serving; no USDA entry
Nannochloropsis is a marine microalga rich in EPA omega-3. See which forms are sold, what the few human trials found, safety data, and its EU and US status.
Gelidium spp., Gracilaria spp., extract of red seaweeds
Normal serving (USDA): 2 tablespoons raw agar (about 10 g); no USDA portion for dried agar
Agar (agar-agar) from red seaweed: a vegetarian gelling agent. USDA values, what the EU safety review found, the dry-swallowing and bowel-blockage caution, and why diet claims lack trials.
Chondrus, Kappaphycus, Eucheuma (extract)
Normal serving (USDA): No serving: food additive used in small amounts
Carrageenan (E407) from red seaweeds: food-grade versus degraded poligeenan, what EFSA, JECFA and FDA say, the Tobacman critiques, small human trials, and the 2016 organic board vote.
Laminaria spp., Macrocystis pyrifera, Ascophyllum nodosum, extract of brown seaweeds
Normal serving (USDA): No standard serving; alginate is used as an additive or medicine
Alginate from brown seaweed as a food additive, a Gaviscon-type reflux medicine and a diet supplement: what regulators and trials found, and what they did not show.
Sulfated polysaccharide of brown seaweeds
Normal serving (USDA): No official serving found
Fucoidan, the sulfated sugar from brown seaweeds, sold as capsules and powders: what human trials found, the blood-thinner caution, iodine and metal questions, and lab-only claims.
Fucoxanthin (carotenoid pigment of brown seaweeds and diatoms)
Normal serving (USDA): No official serving; no USDA entry
Fucoxanthin is an orange pigment of brown seaweeds sold for weight loss. See the human trials, absorption, safety data and the iodine and metal cautions.
Arthrospira platensis (pigment-protein extract)
Normal serving (USDA): No official serving; food color used at good manufacturing practice levels
Phycocyanin, the blue pigment from spirulina used in drinks, candy and lattes: FDA color rules, thin human evidence, supplement form, allergy and color stability.
Noodles made from kelp (alginate) gel, Laminaria / Saccharina kelp with sodium alginate
Normal serving (USDA): 4 ounces (about 113 g) per the manufacturer label
Kelp noodles are clear, crunchy noodles made from kelp and alginate gel. What labels show, iodine and thyroid cautions, and what low-carb and weight claims can and cannot say.
Roasted, seasoned Pyropia (nori) sheets
Iodine
Normal serving (USDA): label serving (tests read: 1.3 g to 3 g)
Roasted, seasoned nori snack sheets: how much iodine and sodium tests found, what it means for children eating them daily, and how to read the label.
Rice seasoning with nori, sesame and salt
Normal serving (USDA): 1 tablespoon (6 g), from one furikake label
Furikake is a Japanese rice seasoning with nori, sesame and salt. What is in it, sodium, sugar, allergens and iodine, and what research does not show.
Salt blended or made with seaweed
Normal serving (USDA): No official serving found
Seaweed salt explained: what the name can mean, why it is still salt, how kelp iodine makes labels matter, what sodium-cutting research exists, and what we could not find.
Seasoned wakame or mixed seaweed salad
Normal serving (USDA): No official serving; packages set their own
Seaweed salad (chuka wakame) as sold in restaurants and stores: sodium, added sugar, colors, iodine, Listeria findings and what we could and could not verify.
Laminaria japonica, Saccharina japonica
Iodine
Normal serving (USDA): No official serving found; USDA has no dashi entry
Dashi, the Japanese stock made from kombu: kombu-only vs kombu-and-bonito versions, how much iodine can end up in the stock, fish allergy, instant dashi labels and what is known.
Microalgal oil
Astaxanthin, 3,3'-dihydroxy-beta,beta-carotene-4,4'-dione
Fucus vesiculosus
Whole plant / above-ground
Bladderwrack (Fucus vesiculosus), a brown seaweed: why its iodine can disturb the thyroid, the arsenic and heavy-metal concern, and what EU regulators and trials say about weight-loss claims.
Chondrus crispus
Whole plant / above-ground
Irish moss or sea moss (Chondrus crispus): what we found on iodine, heavy metals, carrageenan and thyroid cautions, and why the popular sea moss gel claims are not backed by human trials.
Saccharina japonica, Ascophyllum nodosum
Whole plant / above-ground
Kelp (Saccharina japonica, also Ascophyllum nodosum), a brown seaweed: why its iodine can upset the thyroid, the arsenic concern, and how little human evidence supports health claims.
Arthrospira platensis
Whole plant / above-ground
Spirulina (Arthrospira platensis), a blue-green alga sold as powder and tablets: what trials show for cholesterol and blood pressure, plus contamination, allergy and B12 cautions.
Chlorella vulgaris, Chlorella pyrenoidosa
Whole plant / above-ground
Chlorella (Chlorella vulgaris), a green microalga sold as tablets and powder: what trials found, plus vitamin K and warfarin, allergy, contamination and immune-condition cautions.
No seaweed or alga matches all of these filters. Try removing one. Some topics (for example most herbs) are not seaweeds and algae and live elsewhere on the site.
A link between a seaweed or alga and a topic means the body needs the seaweed or alga for that job, or that low intake is linked to it. It does not mean extra supplements help if your intake is already adequate. See each page’s evidence label.
Kombu, wakame, arame, hijiki, mozuku, kelp and bladderwrack: the big, leathery sea vegetables. Kelp and kombu can hold a lot of iodine; hijiki carries an arsenic advisory.
Nori, dulse, sea moss and Irish moss: the sheets, flakes and gels. Most iodine-friendly of the sea vegetables, and the source of agar and carrageenan.
Sea lettuce, sea grapes and ao-nori: delicate green seaweeds eaten fresh, in salads or as a seasoning.
Spirulina, chlorella, blue-green algae (AFA), dunaliella, euglena, nannochloropsis, algal oil and astaxanthin: single-celled algae sold as powders, tablets and oils. Product quality and contamination matter here.
Agar, carrageenan, alginate, fucoidan, fucoxanthin and phycocyanin: gels, thickeners and concentrated compounds taken from seaweed. A result for an extract does not carry over to the whole seaweed.
Kelp noodles, roasted seaweed snacks, furikake, seaweed salt, seaweed salad and dashi: how seaweed is actually eaten, and what to check on the label.
Seaweed & Algae work alongside other nutrients. Here is what our sources link to them.
Vitamin A: The body can convert beta-carotene to vitamin A.
Vitamin A: Vitamin E and beta-carotene were tested together in the Finnish smoker trial.
Vitamin D: Vitamin D increases calcium absorption; both matter for bones, and treatment of rickets and osteomalacia includes both.
Vitamin D: NHS says vitamin D helps regulate calcium and phosphate.
Vitamin E: MedlinePlus says vitamin E helps the body use vitamin K; both affect blood clotting, which matters for people on blood thinners.
Vitamin E: Vitamin E and selenium were tested together and apart in the SELECT prostate cancer trial.
Vitamin E: Vitamin C and vitamin E were pooled with other antioxidants in the Cochrane mortality review.
Vitamin K: Vitamin D with K2 products exist; the site page does not claim an added benefit.
Vitamin B1 (thiamin): The NHS page covers B vitamins together; MedlinePlus says doctors may recommend other vitamins alongside thiamin for beriberi.
Vitamin B2: MedlinePlus says riboflavin works with the other B vitamins.
Vitamin B3 (niacin): Pellagra comes from too little niacin or tryptophan in the diet, so both matter for avoiding deficiency.
Vitamin B5: MedlinePlus covers pantothenic acid and biotin together; both are needed for growth and metabolism and for making fatty acids.
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Kombu (kelp) as a food: why iodine comes first, USDA values, what studies found on thyroid, body fat and blood pressure, arsenic and cadmium, and who should check with a…
Wakame as a food: iodine is the main safety point, USDA values for raw wakame, miso soup use, what research shows, arsenic and pregnancy notes, and the invasive-species …
Arame as a food: a mild brown seaweed from Japan. Its iodine, cadmium and arsenic as measured in a recent study, why it is not hijiki, and what research does and does no…
Hijiki as a food: why government agencies disagree about its inorganic arsenic, what each one said, its high iodine, what research shows, and how it is cooked and chosen.
Mozuku (Okinawa mozuku, Cladosiphon okamuranus) as a food: the slimy brown seaweed, its fucoidan, what small trials found, and iodine, arsenic and medicine cautions.
Nori (laver) as a food: iodine level, the vitamin B12 question (true versus inactive forms), USDA values for wet laver, snack sheet cautions, and what trials found.
Dulse is a red seaweed from the North Atlantic. What research says about its iodine, protein and metals, who should be careful, and what is hype.
Sea moss (Eucheuma, Kappaphycus, Gracilaria) as a food: what the names mean, USDA values, iodine and metals first, and why "92 minerals" and other claims are not backed.
Sea lettuce (Ulva) as a food: Japanese dried "aosa" nutrient values, high iodine per gram, pollutant questions, what small studies of extracts show, and who should be ca…
Sea grapes (umibudo, Caulerpa lentillifera) as a food: what farm analyses found, raw-food safety, salt and iodine gaps, and what lab and small human studies do and do no…
Ao-nori (green laver) as a food: Japanese dried flake nutrient values, iodine per gram, why it is not nori for B12, salt, naming mix-ups, and who should ask a clinician …
Blue-green algae (AFA) from Klamath Lake sold as capsules and powder: microcystin contamination, what human evidence exists, B12 claims, and cautions.
Dunaliella, a microalga rich in natural beta-carotene: the smokers and lung cancer warning, what small trials found, and how regulators treat it as a color and supplemen…
Euglena, a single-celled alga rich in paramylon beta-glucan: what Japanese and Korean trials found on colds and immunity, EU novel-food safety opinions, and how thin the…
Nannochloropsis is a marine microalga rich in EPA omega-3. See which forms are sold, what the few human trials found, safety data, and its EU and US status.
Agar (agar-agar) from red seaweed: a vegetarian gelling agent. USDA values, what the EU safety review found, the dry-swallowing and bowel-blockage caution, and why diet …
Carrageenan (E407) from red seaweeds: food-grade versus degraded poligeenan, what EFSA, JECFA and FDA say, the Tobacman critiques, small human trials, and the 2016 organ…
Alginate from brown seaweed as a food additive, a Gaviscon-type reflux medicine and a diet supplement: what regulators and trials found, and what they did not show.
Fucoidan, the sulfated sugar from brown seaweeds, sold as capsules and powders: what human trials found, the blood-thinner caution, iodine and metal questions, and lab-o…
Fucoxanthin is an orange pigment of brown seaweeds sold for weight loss. See the human trials, absorption, safety data and the iodine and metal cautions.
Phycocyanin, the blue pigment from spirulina used in drinks, candy and lattes: FDA color rules, thin human evidence, supplement form, allergy and color stability.
Kelp noodles are clear, crunchy noodles made from kelp and alginate gel. What labels show, iodine and thyroid cautions, and what low-carb and weight claims can and canno…
Roasted, seasoned nori snack sheets: how much iodine and sodium tests found, what it means for children eating them daily, and how to read the label.
Furikake is a Japanese rice seasoning with nori, sesame and salt. What is in it, sodium, sugar, allergens and iodine, and what research does not show.
Seaweed salt explained: what the name can mean, why it is still salt, how kelp iodine makes labels matter, what sodium-cutting research exists, and what we could not fin…
Seaweed salad (chuka wakame) as sold in restaurants and stores: sodium, added sugar, colors, iodine, Listeria findings and what we could and could not verify.
Dashi, the Japanese stock made from kombu: kombu-only vs kombu-and-bonito versions, how much iodine can end up in the stock, fish allergy, instant dashi labels and what …
Iodine in seaweed by type, from kombu to nori, wakame, hijiki, dulse and spirulina, compared with intake figures, plus what it can mean for your thyroid.
Why several countries advise against hijiki, how arsenic differs by type, what surveys found for cadmium, lead and mercury in seaweed and kelp tablets, and who should ta…
Does seaweed give you vitamin B12? Nori, spirulina, chlorella, AFA and kelp checked: true B12 versus look-alike analogues, what human studies measured, and the plain bot…
A practical guide to buying, reading labels, soaking, cooking and storing seaweed, with what official sources say about iodine, arsenic, allergens and who should ask a c…
Blue-green algae supplements (AFA, spirulina): what microcystins are, what testing found, the Oregon 1 mcg/g limit, who should ask first, and what to ask a seller.
What health agencies say about seaweed, kelp, hijiki and algae products in pregnancy and breastfeeding, and what Korean and other studies of high-seaweed diets found.
Seaweed and algae with warfarin, thyroid drugs, kidney disease, blood pressure medicines, PKU, allergy and swallowing problems: what official sources say, and who to ask.
Sea moss and sea moss gel checked against sources: iodine and thyroid first, then heavy metals, microbes, and what human research does and does not show for common claims.
Sea Moss Gel: Claims CheckedSpirulina versus chlorella: how the two microalgae differ, what meta-analyses of trials found, shared contamination and allergy cautions, and why no ranking is possible.
Spirulina vs ChlorellaCan seaweed affect your thyroid? How much iodine seaweed products contain, what official upper limits say, what studies found, and who should ask a clinician first.
Seaweed, Iodine and ThyroidSeaweed, sea moss and kelp explained plainly: why iodine content varies so widely, what is known about thyroid effects and arsenic, and what research does and does not show.
Seaweed, Sea Moss and KelpWhat research and thyroid and food-safety bodies say about kelp and seaweed supplements, including very variable iodine content, thyroid problems, arsenic in some seaweeds and who should ask first.
Kelp and Seaweed Supplements: Iodine Content and RisksWhich foods supply iodine, with amounts per serving from NIH and NHS sources, why seaweed and dairy vary so much, and where too much iodine can become a problem.
Foods High in Iodine: Salt, Seaweed, Dairy and FishWhat research shows about EPA and DHA status in vegetarians and vegans, what algal oil studies found, which plant foods supply ALA, and what dietetic and official sources say.
Omega-3 for Vegetarians and Vegans: Algal DHA and EPAFish oil and algal oil compared for EPA and DHA: what blood-level trials show, which results come from company-linked studies, and why health outcomes have not been compared head to head.
Fish Oil vs Algal OilLand vegetables and leafy greens, including kimchi.
VegetablesMiso, soy sauce and other ferments often made with or served with seaweed.
Fermented FoodsIodine as a nutrient: how much the body needs and the upper limits.
Vitamins & Supplements: IodineContent last updated . This section has not been medically reviewed.
