Health Care Professional Information
Sea kelp, Brown kelp seaweed, Sea wrack, Marine oak
Maine sea coast vegetables
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 and has been proposed as a weight loss supplement. No clinical studies have verified this effect. Bladder wrack is believed responsible for the reduced risk of estrogen-related cancers in Asian populations (1) and may improve menstrual symptoms (1). Further studies are needed to clarify such effects.
Bladder wrack extract also demonstrated chemopreventive (7), anti-collagenase and antioxidant properties (6); topical application of bladder wrack extract may help improve skin (2).
Bladder wrack should be used with caution in patients with hormonal-sensitive cancers.
Atlantic sea kelp, seaweed
- Weight loss
- Skin care
- Menstrual abnormalities
Mechanism of Action
Bladder wrack extract is rich in iodine and has been used as a natural supplement for thyroid disorder and for obesity. It exhibits antiestrogenic effects. Bladder wrack has also been shown to lower plasma cholesterol levels by competitive inhibition via fucosterols. As cholesterol is a precursor for the 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, treatment with bladder wrack lengthened overall estrous cycles and reduced circulating 17,beta-estradiol levels (4). Bladder wrack and related seaweed species have been shown to exhibit anti-hypertensive effects via angiotensin-I-converting enzyme inhibition. The antibacterial and antioxidant properties are thought to be due to its polyphenolic contents (1). Topical bladder wrack extract reduced skin thickness and improved the mechanical/elastic properties (2).
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).
Bladder wrack acts as an estrogenic receptor modulator and should be used with caution in patients with hormonal-sensitive cancers.
- Consumption of a slimming product containing 20 different herbs, bladder wrack being one of them, resulted in hemorrhagic cystitis in a 33-year-old woman. Symptoms resolved after discontinuing the product (8).
- Theoretically, bladder wrack may have an additive effect when taken with cholesterol-lowering and antihypertensive medications (1).
- Bladder wrack inhibits cytochrome P450 enzymes, thereby affecting the cellular concentration of drugs that are metabolized by these enzymes (7).
Literature Summary and Critique
Clinical trials have not been conducted with bladder wrack.
- 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.
- 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.
- 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.
- Moro CO, Basile G. Obesity and medicinal plants. Fitoterapia 2000;71 Suppl 1:S73-82.
- Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant 1998;13(2):526-7.
- 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.
- 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.
- Catania MA, Oteri A, Caiello P, et al. Hemorrhagic cystitis induced by an herbal mixture. South Med J. 2010 Jan;103(1):90-2.
How It Works
Bottom Line: The claims of beneficial effects of bladder wrack have not been confirmed in clinical trials.
Bladder wrack extract is rich in iodine and is claimed to stimulate thyroid activity to treat obesity. There is no evidence to support this. Women who took bladder wrack showed improvement in their menstrual symptoms. Topical application of a bladder wrack extract showed benefits for skin. Further studies are needed to confirm these effects.
- Menstrual abnormalities
In a small study, women who took bladder wrack reported improvement in menstrual symptoms.
- Skin care
Results of a clinical trial showed that topical bladder wrack extract can improve the skin.
- Weight loss
This use is not supported by scientific evidence.
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.
There are no clinical data to support this use.
Bladder wrack has not been studied in clinical trials.
Patients with thyroid disorder or hormonal-sensitive cancers should talk to their doctors before using bladder wrack.
- Consumption of a slimming product containing 20 different herbs, bladder wrack being one of them, resulted in hemorrhagic cystitis (inflammation of the urinary bladder) in a 33-year-old woman. Symptoms resolved after discontinuing the product.
Bladder wrack is often referred to as brown kelp but it should not be confused with “kelp,” another species of seaweed.
Last updated: March 14, 2012