Written by the Plenthera team (orthomolecularly trained). Scientifically reviewed in April 2026. Last updated: April 30, 2026.
Seaweed is not a single ingredient but a whole family — kelp, wakame, kombu, nori, dulse, arame. Each with its own flavor, nutritional profile, and culinary application. Together they provide what is rare in Western diets: iodine in concentrated form, plus potassium, calcium, magnesium, and alginates. At Plenthera, you'll find seaweed as a premium wholefood — dried sheets, flakes, powders, and standardized supplements. With explicit attention to iodine dosage, as seaweed can quickly result in high levels.
Which seaweed is right for you?
| Type | Iodine | Best for |
|---|---|---|
| Kelp/kombu | Very high | Standardized supplements, soup |
| Wakame | Moderate | Soup, salad, mineral supplementation |
| Nori | Low | Sushi, snack |
| Dulse | Moderate | Flavor, iron source |
| Arame | Moderate | Salad, flavor |
What is seaweed?
Seaweed is a collective term for various edible macroalgae — brown algae, green algae, and red algae. The main types in food and supplements are kelp/kombu (Laminaria/Saccharina), wakame (Undaria pinnatifida), nori (Pyropia/Porphyra), dulse (Palmaria palmata), and arame (Eisenia bicyclis).
In Asian food traditions — especially Japan, Korea, China — seaweed has been a daily ingredient for thousands of years. Sushi rice rolled in nori, kombu in dashi soup, wakame in miso soup, hijiki in salads. For Western cuisine, seaweed is a relatively recent discovery, but its growth is strong — both as a culinary ingredient and as a supplement category.
What distinguishes seaweed nutritionally is the combination of iodine and minerals. It is by far the most concentrated natural source of iodine — kelp can contain up to 8,000 µg of iodine per gram of dry weight, while the RI is 150 µg/day. This makes seaweed intake a double-edged sword: a rich food source, but also easy to exceed the UL (upper limit) — especially with kelp and kombu.
For those considering seaweed, there are three points of attention. First: iodine content varies greatly by species. Second: avoid hijiki due to arsenic content (advised against by NVWA and UK FSA). Third: B12 claims for vegans are complicated — many seaweeds contain pseudo-B12, which is not recognized as active B12 by humans. Also, check our chlorella category and spirulina category where the B12 aspect also plays a role.
Science, minerals, and EFSA status
For seaweed as a food category, there are no overarching EFSA claims. However, individual minerals in seaweed (iodine, calcium, magnesium, iron) each have their own recognized EFSA claims — applicable to seaweed supplements that meet the threshold for the respective minerals.
Research into seaweed focuses on antioxidant activity (due to fucoxanthin in brown algae), thyroid issues (iodine), gut health (alginates as a prebiotic), and cardiovascular research. Clinical evidence for specific health effects is predominantly small-scale.
We do not make literal claims about the specific effects of seaweed. For Hashimoto's, pregnancy, or when using thyroid medication: consult a doctor beforehand. Avoid hijiki due to the arsenic issue.
The six main seaweeds — what are the differences?
Kelp / Kombu (Laminaria, Saccharina): Brown seaweed, highest iodine content. Classic in Japanese dashi soup. In supplements often standardized for iodine content.
Wakame (Undaria pinnatifida): Brown seaweed, mild in taste. Classic in miso soup. Lower iodine than kelp, mineral-rich.
Nori (Pyropia/Porphyra): Red seaweed (dried black-green). Used for sushi rolls. Some types contain real B12.
Dulse (Palmaria palmata): Red seaweed, mild flavor. Good iron source, moderate iodine.
Arame (Eisenia bicyclis): Brown seaweed, mild sweet flavor. Rich in minerals.
Hijiki (Sargassum fusiforme): CONTAINS HIGH ARSENIC LEVELS. UK FSA and NL NVWA advise against it. We do not carry hijiki.
The seaweed forms at Plenthera
Kelp standardized (capsules)
Concentrated kelp standardized for iodine content (typically 150 µg per serving). For exact dosing — without guessing about iodine content.
Dried Wakame
Classic for soups or salads. Mineral-rich, milder iodine content.
Nori sheets
For sushi rolls or as a crispy snack. Small iodine content, B12 question controversial.
Seaweed mix powder
Mixed seaweeds as a seasoning — sprinkle over salads, in smoothies or soups.
Dulse flakes
Mild salty-red seaweed — alternative to salt in dishes.
How to use seaweed?
Simple basic approach for seaweed:
- Determine your goal: iodine supplementation (standardized kelp), culinary use (wakame, nori, arame), or mineral supplementation (all).
- For iodine supplements: choose kelp standardized for iodine content. Follow label — avoid EFSA UL (600 µg/day).
- For culinary use: wakame in miso soup (5-10 g fresh), nori for sushi (1-2 sheets per meal), arame in salads.
- Avoid hijiki — advised against by government agencies (arsenic).
- For Hashimoto's, thyroid medication, or pregnancy: consult a doctor beforehand before consuming high amounts of seaweed.
- B12 for vegans: do NOT use seaweed as the sole source of B12 — choose a methylcobalamin supplement.
- Store dried seaweed dry and away from light.
Myths and misconceptions about seaweed
Myth 1: "All seaweeds are a good vegan B12 source."
Incorrect. Many seaweeds contain pseudo-B12 that is not recognized as active B12 by humans. Some nori types do contain real B12, but for certainty, vegans use methylcobalamin supplements.
Myth 2: "The more seaweed, the better."
Incorrect and risky. Kelp can quickly exceed the UL for iodine (600 µg/day). In Hashimoto's, high iodine intake can worsen the condition. Dose consciously.
Myth 3: "Hijiki is healthier than other seaweeds."
Incorrect. Hijiki contains high levels of inorganic arsenic — advised against by UK FSA and NL NVWA for regular use. Other seaweeds do not have this issue.
Myth 4: "Seaweed for iodine is always more reliable than a supplement."
Not automatically. Seaweed iodine content varies greatly (factor 50-100 difference between types and batches). For exact dosing: standardized kelp supplement or potassium iodide.
Combining seaweed with other supplements
Seaweed is often combined for its mineral content. Popular combinations include:
- Iodine category: for precise dosing alongside wholefood seaweed.
- Multiminerals: for broad mineral balance.
- Spirulina/chlorella: superfood stack.
- Vitamin D: for thyroid immune support.
- B12 methylcobalamin: for vegans (replaces seaweed B12 claim).
Frequently Asked Questions
What is seaweed?
Collective term for edible macroalgae. Brown algae (kelp, wakame), green algae, and red algae (nori, dulse).
Which seaweeds are there?
Main types: kelp/kombu, wakame, nori, dulse, arame. Avoid hijiki (arsenic).
How much seaweed per day?
Small dosage: 1-3 nori sheets, 2-5 g wakame, or kelp supplement with 100-300 µg iodine per serving.
Seaweed for thyroid — does it work?
In case of iodine deficiency: yes. For Hashimoto's: caution. EFSA claim for iodine for thyroid (if threshold met).
What is the difference between kelp and wakame?
Kelp: highest iodine, for soup and supplements. Wakame: milder, for miso soup and salads.
Does seaweed contain vitamin B12?
Some nori types have real B12. Many seaweeds have pseudo-B12. For vegans: methylcobalamin supplement is more reliable.
Does seaweed have side effects?
With high intake (especially kelp): UL of iodine may be exceeded. For Hashimoto's/thyroid medication: caution.
Which seaweed for iodine?
Standardized kelp is most concentrated. For exact dosing: potassium iodide.
Seaweed vegan?
Yes, plant-based. But B12 claim unreliable for vegans.
What is hijiki and can I eat it?
Contains high arsenic levels. Advised against by government agencies. We do not carry it.
Sources
Disclaimer: This text is intended for informational purposes only and does not replace medical advice. Seaweed is a dietary supplement, not a medicine. In case of doubt or if using medication, we recommend consulting a doctor or orthomolecular therapist first.