- Sea kelp
- Brown kelp seaweed
- Sea wrack
- Marine oak
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.
How It Works
Claims of beneficial effects of bladder wrack have not been confirmed in clinical studies.
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.
Bladder wrack is often referred to as brown kelp but it should not be confused with “kelp,” which is another species of seaweed.
Evidence is lacking to support this claim.
Results of a small clinical study showed that topical bladder wrack extract can improve the elasticity of skin.
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.
Evidence is lacking to support this claim.
In a small study, women who took bladder wrack reported improvement in menstrual symptoms.
Do Not Take If
- If you are taking Cytochrome P450 substrates: Bladder wrack inhibits cytochrome P450 enzymes, thereby affecting the cellular concentration of drugs that are metabolized by these enzymes. Clinical relevance is not known.
- If you are taking Amiodarone: Bladder wrack decreased the bioavailability of amiodarone (used to treat arrhythmia) in a murine model. Clinical relevance is not known.
For Healthcare Professionals
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.
Bladder wrack extracts demonstrated chemopreventive (7), anticollagenase and antioxidant properties (6). in preclinical studies. Preliminary clinical data suggest that dietary bladderwrack may prolong the length of menstrual cycle and exert antiestrogenic effects in premenopausal women (1). Topical application of bladder wrack extract helped reduce thickness of skin and improve its elasticity (2). In another study, a bladder wrack extract was reported to be safe and well tolerated, but was only as effective as a placebo for reduction of osteoarthritic symptoms (12).
Mechanism of Action
Bladder wrack extract is rich in iodine and has been used as a supplement for thyroid disorder and for obesity. It has 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).
A bladder wrack extract inhibited the cell cyle of proliferating pancreatic cancer cells due to the up-regulation of cell cycle inhibitors, independent of caspases. Also, it showed low cytotoxic activity against non-malignant resting T cells and erythrocytes. Accelerated killing was observed in combination with inhibitors of autophagy (11).
- 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).
- Cytochrome P450 substrates: Bladder wrack inhibits cytochrome P450 enzymes, thereby affecting the cellular concentration of drugs that are metabolized by these enzymes (7) (13). Clinical relevance is not known.
- Amiodarone: Bladder wrack decreased the bioavailability of amiodarone (used to treat arrhythmia) in a murine model (10). Clinical relevance is not known.