Ecklonia cava (brown seaweed polyphenols)

Also called Ecklonia cava, Ecklonia cava Kjellman, kajime, Ecklonia cava polyphenols, ECP, Seapolynol.

Best grade C across 8 graded outcomes Botanical Last checked Oct 21, 2026

The short answer

From 10 sources

Ecklonia cava is a brown seaweed sold as a phlorotannin-rich extract. Small Korean trials, several linked to companies selling the extract, reported modest drops in body fat, LDL cholesterol and after-meal glucose over 12 weeks. Evidence is thin and unreplicated. The EU caps intake of its authorised extract and requires warnings for thyroid disease because the extract contains iodine.

Every graded outcome on this page

8 rows · line = participants

Grade CFasting glucose and cholesterol (marine algal polyphenols)Overall evidencen 271
Grade CCough, sputum and breathlessness scoresRespiratory symptomsn 106
Grade CBody fat and waist size in overweight adultsBody fatn 97
Grade CTotal and LDL cholesterol in overweight adultsCholesteroln 97
Grade CAfter-meal glucose in prediabetesBlood glucosen 80
Grade DCholesterol in people with high cholesterolCholesteroln 46
Grade DGlucose after a 75 g carbohydrate loadBlood glucosen 20
Grade DTime to exhaustion in exerciseExercisen 20
5 more graded outcomes, in the evidence chapter

Key facts

Body fat and cholesterol: 72 or 144 mg/day of an E. cava polyphenol extract for 12 weeks lowered body fat ratio, waist size, total and LDL cholesterol versus placebo in 97 overweight Korean adults¹
After-meal glucose: 1,500 mg/day of a dieckol-rich extract lowered post-meal glucose versus placebo over 12 weeks in 80 adults with prediabetes; insulin and C-peptide did not differ from placebo²
EU intake limit: EFSA judged the authorised phlorotannin extract safe up to 263 mg/day for adults, 230 mg/day above age 14 and 163 mg/day at ages 12-14⁸
Thyroid warning: EU rules require labels saying the extract is not for people with or at risk of thyroid disease, or for use alongside other iodine supplements⁹
Evidence base: A systematic review found only five randomized trials (271 adults) of marine algal polyphenols, with small-to-medium effects that were not yet shown to be consistent⁷

What it is

Ecklonia cava is an edible brown seaweed from Korea and Japan; supplements are extracts rich in phlorotannins such as dieckol.

How it works

Proposed

Phlorotannins such as dieckol inhibited the starch- and sugar-digesting enzymes alpha-glucosidase and alpha-amylase in laboratory tests and blunted post-meal glucose in diabetic mice. Antioxidant and circulatory effects are also proposed. How much of this applies to people is unknown.^10,2

Forms, side by side

3 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.

Ecklonia cava (brown seaweed polyphenols) forms compared

3 forms

Ecklonia cava (brown seaweed polyphenols) forms compared: 3 forms by 3 attributes. Empty cells are labelled No data yet, or Not graded in the evidence row.
3 forms	E. cava polyphenol (phlorotannin) extract, e.g. Seapolynol or ECP	Dieckol-rich extract (AG-dieckol)	E. cava with Chrysanthemum indicum (two-herb complex)
Absorption in people	No human absorption data in the cited abstracts; EFSA notes the extract also supplies iodine.⁸	Not measured in the trial abstract.²	Not measured.⁶
GI tolerance	No significant adverse events in 12-week trials at 72-400 mg/day.^1,5	No significant adverse events at 1,500 mg/day for 12 weeks.²	No severe adverse events over 12 weeks.⁶
Studied for	Body fat, cholesterol, exercise	After-meal glucose	Respiratory symptoms

E. cava polyphenol (phlorotannin) extract, e.g. Seapolynol or ECP
Absorption in people
No human absorption data in the cited abstracts; EFSA notes the extract also supplies iodine.⁸
GI tolerance
No significant adverse events in 12-week trials at 72-400 mg/day.^1,5
Studied for
Body fat, cholesterol, exercise
Dieckol-rich extract (AG-dieckol)
Absorption in people
Not measured in the trial abstract.²
GI tolerance
No significant adverse events at 1,500 mg/day for 12 weeks.²
Studied for
After-meal glucose
E. cava with Chrysanthemum indicum (two-herb complex)
Absorption in people
Not measured.⁶
GI tolerance
No severe adverse events over 12 weeks.⁶
Studied for
Respiratory symptoms

What the human research says

Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.

Trial map

8 graded outcomes, largest study first

8 graded outcomes: 6 improved, 2 mixed. The largest, a 2018 systematic review of 271 people on fasting glucose and cholesterol (marine algal polyphenols), found mixed results.

By sizeTable

1Fasting glucose and cholesterol (marine algal polyphenols)

Mixed · Grade C · Systematic review, 271 people, 2018

Adults in randomized trials of marine algal polyphenol extracts

Dose, result and source

Every graded outcome on this page, largest study first
Outcome	Found	People	Study	Who was studied
Fasting glucose and cholesterol (marine algal polyphenols)	Mixed	271	Grade C · Systematic review, 2018	Adults in randomized trials of marine algal polyphenol extracts
Cough, sputum and breathlessness scores	Improved	106	Grade C · RCT, 2026	Korean adults with respiratory symptoms (multicentre)
Body fat and waist size in overweight adults	Improved	97	Grade C · RCT, 2012	Overweight Korean adults (mean BMI 26.5)
Total and LDL cholesterol in overweight adults	Improved	97	Grade C · RCT, 2012	Overweight Korean adults (mean BMI 26.5)
After-meal glucose in prediabetes	Improved	80	Grade C · RCT, 2015	Adults with prediabetes
Cholesterol in people with high cholesterol	Improved	46	Grade D · Open-label trial, 2012	Korean adults with high total or LDL cholesterol
Glucose after a 75 g carbohydrate load	Mixed	20	Grade D · RCT, 2023	Adults with prediabetes in Saudi Arabia
Time to exhaustion in exercise	Improved	20	Grade D · Crossover RCT, 2010	Male college students aged 18-23

Every graded row

8 rows

Form tested

Showing 8 of 8 outcomes. Human trials only.

Grade CFasting glucose and cholesterol (marine algal polyphenols)Overall evidenceSmall, unconfirmed effectsSystematic review · 5 studies
n 271 · 2018

Mixed Small-to-medium favourable effects on fasting glucose, total and LDL cholesterol, but the authors judged the evidence inadequate to confirm consistent effects.

Design: Systematic review, 5 studies, n = 271, 2018
Population: Adults in randomized trials of marine algal polyphenol extracts
Form: Polyphenol-rich brown seaweed extracts, including E. cava
Dose: Varied by trial
Duration: Varied by trial
Source: Reference 7 · PubMed 28414549 (opens PubMed)

Grade CCough, sputum and breathlessness scoresRespiratory symptomsBetter symptom scoresRCT
n 106 · 2026

Improved The breathlessness, cough and sputum scale (total, breathlessness and sputum scores), FEV1 and visual-scale cough and sputum ratings improved versus placebo; quality-of-life (SGRQ) and dyspnoea (mMRC) scores did not differ. No severe adverse events.

Design: RCT, n = 106, 2026
Population: Korean adults with respiratory symptoms (multicentre)
Form: E. cava plus Chrysanthemum indicum extract complex
Dose: Twice daily (amount not stated in the abstract)
Duration: 12 weeks
Source: Reference 6 · PubMed 41523268 (opens PubMed)

Grade CBody fat and waist size in overweight adultsBody fatLess body fat vs placeboRCT
n 97 · 2012

Improved Both doses reduced BMI, body fat ratio, waist circumference and waist/hip ratio more than placebo; only the higher dose lowered fasting glucose and systolic blood pressure. No significant adverse events.

Design: RCT, n = 97, 2012
Population: Overweight Korean adults (mean BMI 26.5)
Form: E. cava polyphenol extract (ECP)
Dose: 72 or 144 mg/day
Duration: 12 weeks
Source: Reference 1 · PubMed 21717516 (opens PubMed)

Grade CTotal and LDL cholesterol in overweight adultsCholesterolLower total and LDL cholesterolRCT
n 97 · 2012

Improved Total cholesterol, LDL cholesterol and the total/HDL ratio fell more than with placebo at both doses; HDL rose only at 144 mg/day.

Design: RCT, n = 97, 2012
Population: Overweight Korean adults (mean BMI 26.5)
Form: E. cava polyphenol extract (ECP)
Dose: 72 or 144 mg/day
Duration: 12 weeks
Source: Reference 1 · PubMed 21717516 (opens PubMed)

Grade CAfter-meal glucose in prediabetesBlood glucoseLower post-meal glucoseRCT
n 80 · 2015

Improved Post-meal glucose fell significantly versus placebo. Insulin and C-peptide fell within the extract group but did not differ significantly from placebo. No significant adverse events.

Design: RCT, n = 80, 2015
Population: Adults with prediabetes
Form: Dieckol-rich E. cava extract (AG-dieckol)
Dose: 1,500 mg/day
Duration: 12 weeks
Source: Reference 2 · PubMed 25608849 (opens PubMed)

Grade DCholesterol in people with high cholesterolCholesterolLDL 161 to 146 mg/dL (no control)Open-label trial
n 46 · 2012

Improved Total cholesterol fell from 244 to 225 mg/dL and LDL from 161 to 146 mg/dL, with lower CRP and hip circumference; no significant adverse effects.

Design: Open-label trial, n = 46, 2012
Population: Korean adults with high total or LDL cholesterol
Form: E. cava polyphenol extract (Seapolynol)
Dose: 400 mg once daily
Duration: 12 weeks
Source: Reference 5 · PubMed 23126663 (opens PubMed)

Grade DGlucose after a 75 g carbohydrate loadBlood glucoseLower late glucose onlyRCT
n 20 · 2023

Mixed Glucose was lower than placebo at 90 and 120 minutes (108.1 vs 122.2 and 101.3 vs 112.9 mg/dL) but not at 30 or 60 minutes, and the overall glucose area under the curve and insulin did not differ.

Design: RCT, n = 20, 2023
Population: Adults with prediabetes in Saudi Arabia
Form: E. cava seaweed extract
Dose: 600 mg, single dose
Duration: Single dose (2-hour test)
Source: Reference 3 · PubMed 36789057 (opens PubMed)

Grade DTime to exhaustion in exerciseExercise+2.4 min to exhaustionCrossover RCT
n 20 · 2010

Improved Time to exhaustion was 2.39 minutes longer than with placebo; VO2max was 6.5% higher but not significantly.

Design: Crossover RCT, n = 20, 2010
Population: Male college students aged 18-23
Form: E. cava polyphenol drink
Dose: One drink 30 minutes before exercise (amount not stated in the abstract)
Duration: Single dose, two sessions one week apart
Source: Reference 4 · PubMed 20190354 (opens PubMed)

What the numbers add up to

Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.

One research network dominates

The three E. cava polyphenol trials on body fat, cholesterol and exercise share co-authors, the lead author of the largest lists a company research centre, and no independent group has replicated them.^1,4,5

Glucose results are early and narrow

Both glucose trials measured after-meal glucose; neither showed a clear insulin effect versus placebo.^2,3

Studied doses

Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.

Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.

Doses studied in human trials

Doses studied in human trials ranged from 72 mg/day of a polyphenol extract to 1,500 mg/day of a dieckol-rich extract for 12 weeks, plus single doses of 600 mg before a glucose test. These are research doses, not recommendations, and some exceed the EU's 263 mg/day adult limit for its authorised extract.^1,2,3,8

Interactions and safety

Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.

What Ecklonia cava meets

1 cited row

Medicines 0

No medicine rows in our sources.

Ecklonia cava0 medicines · 1 supplement

Supplements and foods 1

Drug label or FDA notice

Interactions

1 agent

Published interactions, grouped by kind
Agent	What the source says	Evidence
Other supplements1
Other iodine-containing supplementse.g. Iodine, kelp, multivitamins with iodine	The extract contains iodine; EU rules say it should not be used together with other iodine supplements because total intake could exceed the upper limit.^9,8	Drug label

Check with what you take

Kept on this device only

Add what you take. We list every interaction our evidence profiles cite between Ecklonia cava and your picks, and between your picks.

Add a supplement or medicine

Most cited:

Add a supplement or medicine you take to check it against Ecklonia cava.

Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.

Who should be careful

4 groups

People with thyroid disease or at risk of it: Because the extract supplies iodine, EFSA flagged a concern for people at risk of thyroid disease, and EU labels must say it is not for them.^8,9
Children under 12: The EU authorisation excludes children under 12 and sets lower maximums for ages 12-14 and 14-18.^9,8
Pregnancy and breastfeeding: The cited trials enrolled non-pregnant adults only, so there are no human safety data for pregnancy or breastfeeding.^1,2
People on diabetes medicines: A 12-week trial in 80 adults with prediabetes found a dieckol-rich extract (1,500 mg/day) lowered after-meal glucose versus placebo. People with diabetes were not studied and the extract has not been tested alongside glucose-lowering drugs, so any extra drop in blood sugar from combining them is theoretical; let your prescriber know and check glucose more closely when starting.²

How to read the label

What to check on the Supplement Facts panel.

How to read the label

2 checks

Extract amount vs phlorotannin amount

Trials used different products: a polyphenol extract at 72-400 mg/day and a dieckol-rich extract at 1,500 mg/day. Milligrams of one product are not equivalent to another.^1,2,5

Iodine

EU-authorised products must carry thyroid and iodine warnings. The EU specification allows 150-650 mg of iodine per kg of extract, which works out at roughly 40-170 micrograms of iodine at the 263 mg/day adult maximum (our arithmetic). Check whether a product lists its iodine content.⁹

Have the bottle? Photograph its Supplement Facts panel and see each line, ecklonia cava (brown seaweed polyphenols) included, beside the doses and forms the trials used in Label X-Ray.

Frequently asked questions

Short answers to common questions; the numbers link to the sources below.

Common questions

6 answers

Does Ecklonia cava help with weight or cholesterol?

One 12-week Korean trial in 97 overweight adults found small drops in body fat and LDL cholesterol versus placebo. Its lead author was company-affiliated and the result has not been independently replicated.¹

Does it lower blood sugar?

A dieckol-rich extract lowered after-meal glucose in 80 adults with prediabetes, and a single dose lowered late glucose readings in a 20-person test. Neither showed a clear insulin effect versus placebo.^2,3

Is Ecklonia cava safe?

Trials up to 12 weeks reported no significant adverse events. EFSA set a maximum of 263 mg/day of the authorised extract for adults and flagged its iodine content for people at risk of thyroid disease.^1,2,8

How long did Ecklonia cava take to show an effect in trials?

The placebo-controlled trials reported their body fat, cholesterol and after-meal glucose results after 12 weeks of daily use. In a single-dose test, 600 mg lowered glucose only at the 90- and 120-minute readings, not at 30 or 60 minutes, and the overall glucose curve did not differ from placebo.^1,2,3

Can I use it with an iodine supplement?

EU rules say products containing the extract should not be used alongside other iodine-containing supplements, because combined iodine intake could exceed the upper limit.⁹

Which Ecklonia cava extract was tested?

Different products: a polyphenol (phlorotannin) extract at 72–400 mg/day for body fat and cholesterol (the 400 mg pilot named Seapolynol), and a dieckol-rich extract (AG-dieckol) at 1,500 mg/day for after-meal glucose. Milligrams of one extract are not equivalent to another, and the EU's 263 mg/day adult maximum applies to its authorised phlorotannin extract.^1,2,5,8

Sources

10 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.

Sources cited on this page

10 sources

1Effects of 12-week oral supplementation of Ecklonia cava polyphenols on anthropometric and blood lipid parameters in overweight Korean individuals: a double-blind randomized clinical trial.RCT Phytother Res, 2012 · PMID 21717516
2Efficacy and safety of a dieckol-rich extract (AG-dieckol) of brown algae, Ecklonia cava, in pre-diabetic individuals: a double-blind, randomized, placebo-controlled clinical trial.RCT Food Funct, 2015 · PMID 25608849
3Effect of seaweed (Ecklonia cava extract) on blood glucose and insulin level on prediabetic patients: A double-blind randomized controlled trial.RCT Food Sci Nutr, 2023 · PMID 36789057
4Effect of supplementation with Ecklonia cava polyphenol on endurance performance of college students.Crossover RCT Int J Sport Nutr Exerc Metab, 2010 · PMID 20190354
5Effects of Ecklonia cava polyphenol in individuals with hypercholesterolemia: a pilot study.Open-label trial J Med Food, 2012 · PMID 23126663
6Efficacy and Safety of Ecklonia cava Kjellman Extract Complex in Respiratory Health: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Clinical Trial.RCT Food Sci Nutr, 2026 · PMID 41523268
7Do marine algal polyphenols have antidiabetic, antihyperlipidemic or anti-inflammatory effects in humans? A systematic review.Systematic review Crit Rev Food Sci Nutr, 2018 · PMID 28414549
8Safety of Ecklonia cava phlorotannins as a novel food pursuant to Regulation (EC) No 258/97.Guideline EFSA J, 2017 · PMID 32625298
9Commission Implementing Regulation (EU) 2018/460 authorising the placing on the market of Ecklonia cava phlorotannins as a novel foodGuideline European Commission (Official Journal of the EU), 2018 · eur-lex.europa.eu
10Dieckol isolated from Ecklonia cava inhibits alpha-glucosidase and alpha-amylase in vitro and alleviates postprandial hyperglycemia in streptozotocin-induced diabetic mice.Animal study Food Chem Toxicol, 2010 · PMID 20600532

What changed

Every dated change to this page: what changed, who made it and why.

Change log

3 entries

Dated changes to this page
Date	Change	Who and why
Oct 21, 2026FAQ, questions, related	Replaced the FAQ item that repeated the page's own 'What is' question with one on how long trials ran before effects were reported, added an FAQ item on which extract was tested, page questions and links to the metabolic and heart goal hubs. Checked: PubMed (2023–2026) found no newer E. cava-specific meta-analysis or RCT beyond the rows already in the table; a 2025 meta-analysis of seaweed in general (PMID 38749056) was not added because it pools many seaweeds. A 2018 sleep trial of a 'phlorotannin supplement' (PMID 29368365) was not added because its abstract does not name the seaweed source. No LiverTox or LactMed entry exists; interactions remain the EU iodine labelling rule and the diabetes-medicine caution.	Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md
Oct 14, 2026all	Initial editorial evidence review (first draft). Every PMID checked against NCBI E-utilities esummary (titles and years taken from the record, none retracted) and the abstract read for each cited row. Studied doses are reported as research doses, not dosing advice.	Writer: Kymata Health EditorialTrigger: new page
Oct 14, 2026who should avoid	Added a caution for people on diabetes medicines (theoretical additive glucose lowering), sourced to PMID 25608849; abstract re-read via NCBI efetch.	Writer: Kymata Health EditorialTrigger: safety sweep: glucose-lowering supplements and diabetes medicines

Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.

Ecklonia cava (brown seaweed polyphenols)

Medicines 0

Supplements and foods 1

Other iodine-containing supplements