Bladder wrack

Purported Benefits, Side Effects & More
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Bladder wrack

Purported Benefits, Side Effects & More
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Bladder wrack

Common Names

  • Sea kelp
  • Brown kelp seaweed
  • Sea wrack
  • Marine oak

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For Patients & Caregivers

Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.

What is it?

Claims of benefit with use of bladder wrack have not been confirmed in clinical studies.



Bladder wrack extract is rich in iodine. Although it is claimed to stimulate thyroid activity to treat obesity, there is no evidence to support this, and data in humans are quite limited.

In one small study, women who took bladder wrack showed improvement in their menstrual symptoms. Other small studies showed only marginal impacts on metabolic and inflammatory responses and that it was no more effective than placebo for osteoarthritis. Topical application of a bladder wrack extract suggest benefits for skin, but further studies are needed to confirm any of these effects.

Bladder wrack is often referred to as brown kelp but it should not be confused with "kelp," which is another species of seaweed.

What are the potential uses and benefits?
  • Weight loss

    Evidence is lacking to support this claim.
  • Skin care

    A small study suggest topical bladder wrack extract may improve skin elasticity.
  • Underactive thyroid

    Bladder wrack is rich in iodine and has been used as a supplement for patients with hypothyroidism caused by iodine deficiency. However, this has not been studied in clinical trials and the dosage used is unclear.
  • Fatigue

    Evidence is lacking to support this claim.
  • Menstrual abnormalities

    In a small study, women who took bladder wrack reported improvement in menstrual symptoms.
What are the side effects?

Case report

  • Consumption of a slimming product containing 20 different herbs including bladder wrack resulted in bladder inflammation in a 33-year-old woman.
What else do I need to know?

Patient Warnings:

Consumption of bladder wrack harvested from polluted waters may cause kidney toxicity due to the presence of heavy metals such as arsenic, cadmium, and mercury.

Do Not Take if:

  • If you are taking CYP450 substrates: Bladder wrack may affect cellular concentrations of drugs metabolized by these enzymes. Clinical relevance is not known.
  • If you are taking amiodarone: In an animal study, bladder wrack decreased bioavailability of this drug, which is used to treat irregular heartbeat. Clinical relevance is not known.
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For Healthcare Professionals

Brand Name
Maine sea coast vegetables
Scientific Name
Fucus vesiculosus
Clinical Summary

Bladder wrack is a seaweed prevalent on the Atlantic and Pacific coasts from Europe to Asia. It is often referred to as brown kelp but it should not be confused with “kelp,” another species of seaweed. Bladder wrack is consumed as food and medicine, and is a rich source of iodine. It is used in traditional medicine to treat hypothyroidism due to iodine deficiency. It is also promoted as a dietary supplement for weight loss.

In preclinical studies, bladder wrack extracts demonstrated anticollagenase, antioxidant, and chemopreventive properties (6) (7).

Data in humans are limited and suggest only marginal impacts on metabolic and inflammatory responses (14) and no more effectiveness than placebo for osteoarthritic symptoms (12). It may prolong the menstrual cycle and exert antiestrogenic effects in premenopausal women (1). Topical applications helped reduce skin thickness and improve elasticity (2). However, additional studies are needed to determine safety and effectiveness of this product for any condition.

Food Sources

Atlantic sea kelp, seaweed

Purported Uses and Benefits
  • Weight loss
  • Skin care
  • Hypothyroidism
  • Fatigue
  • Menstrual abnormalities
Mechanism of Action

Bladder wrack extract is rich in iodine. It may lower plasma cholesterol levels by competitive inhibition via fucosterols. As cholesterol is a precursor for biosynthesis of steroid hormones, a reduction in cholesterol bioavailability may lower circulating estradiol levels, thereby altering menstrual cycling patterns (1). An extract of bladder wrack reduced 17,beta-estradiol levels and also acted as a competitive inhibitor of estradiol binding to alpha- and beta- estrogen receptors in vitro (3). In rats, bladder wrack lengthened overall estrous cycles and reduced circulating 17,beta-estradiol levels (4).

Bladder wrack and related seaweed species exhibit antihypertensive effects via angiotensin-I-converting enzyme inhibition. Antibacterial and antioxidant properties may be due to polyphenols (1). Topical bladder wrack reduced skin thickness and improved the mechanical/elastic properties (2).

Bladder wrack extract inhibited pancreatic cancer cells via upregulation of cell cycle inhibitors, independent of caspases. It showed low cytotoxic activity against nonmalignant resting T cells and erythrocytes (11).

Warnings

Consumption of bladder wrack harvested from polluted waters may cause nephrotoxicity due to the presence of heavy metals such as arsenic, cadmium, and mercury (5).

Adverse Reactions

Case report

  • Consumption of a slimming product containing 20 different herbs including bladder wrack resulted in hemorrhagic cystitis in a 33-year-old woman (8).
Herb-Drug Interactions
  • CYP450 substrates: Bladder wrack may affect the cellular concentration of drugs metabolized by these enzymes (7) (13). Clinical relevance is not known.
  • Amiodarone: In a murine model, bladder wrack decreased bioavailability of this drug which is used to treat arrhythmias (10). Clinical relevance is not known.
Dosage (OneMSK Only)
References
  1. Skibola CF. The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: a case report. BMC Complement Altern Med. 2004;4:10.
  2. Fujimura T, Tsukahara K, Moriwaki S, et al. Treatment of human skin with an extract of Fucus vesiculosus changes its thickness and mechanical properties. J Cosmet Sci 2002;53(1):1-9.
  3. Skibola CF, Curry JD, VandeVoort C, et al. Brown kelp modulates endocrine hormones in female sprague-dawley rats and in human luteinized granulosa cells. J Nutr 2005;135(2):296-300.
  4. Moro CO, Basile G. Obesity and medicinal plants. Fitoterapia 2000;71 Suppl 1:S73-82.
  5. Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant 1998;13(2):526-7.
  6. Thring TS, Hili P, Naughton DP. Anti-collagenase, anti-elastase and anti-oxidant activities of extracts from 21 plants. BMC Complement Altern Med. 2009 Aug 4;9:27.
  7. Parys S, Kehraus S, Krick A, et al. In vitro chemopreventive potential of fucophlorethols from the brown alga Fucus vesiculosus L. by anti-oxidant activity and inhibition of selected cytochrome P450 enzymes. Phytochemistry. 2010 Feb;71(2-3):221-9.
  8. Catania MA, Oteri A, Caiello P, et al. Hemorrhagic cystitis induced by an herbal mixture. South Med J. 2010 Jan;103(1):90-2.
  9. Smith DG, Young EG. On the nitrogenous constituents of Fucus vesiculosus. J Biol Chem. 1953 Dec;205(2):849-58.
  10. Rodrigues M, Alves G, Abrantes J, Falcão A. Herb-drug interaction of Fucus vesiculosus extract and amiodarone in rats: a potential risk for reduced bioavailability of amiodarone in clinical practice. Food Chem Toxicol. 2013 Feb;52:121-8.
  11. Geisen U, Zenthoefer M, Peipp M, et al. Molecular Mechanisms by Which a Fucus vesiculosus Extract Mediates Cell Cycle Inhibition and Cell Death in Pancreatic Cancer Cells. Mar Drugs. 2015 Jul 20;13(7):4470-91.
  12. Myers SP, Mulder AM, Baker DG, et al. Effects of fucoidan from Fucus vesiculosus in reducing symptoms of osteoarthritis: a randomized placebo-controlled trial. Biologics. 2016 May 26;10:81-8.
  13. Mathew L, Burney M, Gaikwad A, et al. Preclinical Evaluation of Safety of Fucoidan Extracts From Undaria pinnatifida and Fucus vesiculosus for Use in Cancer Treatment. Integr Cancer Ther. 2017 Dec;16(4):572-584.
  14. Vodouhè M, Marois J, Guay V, et al. Marginal Impact of Brown Seaweed Ascophyllum nodosum and Fucus vesiculosus Extract on Metabolic and Inflammatory Response in Overweight and Obese Prediabetic Subjects. Mar Drugs. Feb 26 2022;20(3).
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