• Bladderwrack

    Related Terms

    • Black Tang
    • Cut Weed
    • Rockweed
    • Rockwrack
    • Seawrack


    Principal Proposed Uses

    • None

    Other Proposed Uses

    Bladderwrack is a type of seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans. A common food in Japan, it is used as an additive and flavoring in various food products in Europe. Bladderwrack is commonly found as a component of kelp tablets or powders used as nutritional supplements. It is sometimes loosely called kelp, but that term technically refers to a different seaweed.

    What Is Bladderwrack Used for Today?

    Bladderwrack contains high concentrations of iodine , and for this reason it has been recommended as a treatment for hypothyroidism (underactive thyroid gland). 1 However, iodine will only help for the type of hypothyroidism caused by iodine deficiency, which is a relatively rare condition in the developed world. If your iodine levels are not low, taking extra amounts of iodine can cause your thyroid gland to become either over- or underactive, causinghyperthyroidism or hypothyroidism, respectively. Furthermore, the amount of iodine supplied by bladderwrack is unpredictable.
    A component of bladderwrack called alginic acid swells upon contact with water. When taken orally, it forms a type of seal at the top of the stomach, and for this reason is used in over-the-counter preparations for heartburn . The same constituent gives bladderwrack laxative properties, as well. 2
    Other proposed uses of bladderwrack include treating atherosclerosis and strengthening immunity , but there is no meaningful evidence at present that it works for these purposes. 3,4


    It is important not to take bladderwrack in dosages providing more than the recommended daily intake of iodine. For more information on the appropriate intake for various groups of people, see the iodine article. Products that provide bladderwrack should state the amount of iodine they provide. If this information is not there, do not take it.

    Safety Issues

    Studies have found that levels of iodine vary widely among bladderwrack products. 5 Because of this, if you use bladderwrack as a regular supplement, there is a real risk you may receive an overdose of iodine and develop hyperthyroidism or hypothyroidism .
    Bladderwrack and other seaweed preparations can also worsen acne and decrease iron absorption. 6
    Finally, bladderwrack, like other sea plants, can concentrate toxic heavy metals, such as arsenic, from the surrounding sea water. 7 One report suggests that use of a bladderwrack product with a high heavy metal content is responsible for a case of kidney failure. 9 Heavy metals present particular risks for pregnant or nursing women, children, individuals with kidney disease, or anyone using bladderwrack in high doses or over a long period of time.


    1 Newall C, Anderson, LA, Phillipson JD. Herbal Medicines : A Guide for Health-Care Professionals . London, England: Pharmaceutical Press; 1996.

    2 Newall C, Anderson, LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals. London, England: Pharmaceutical Press; 1996.

    3 Criado MT, Ferreiros CM. Immunomodulatory effect produced in mice by a complex-carbohydrate specific lectin-like mucopolysaccharide from Fucus vesiculosus . IRCS J Med Sci . 1983;11:286–287.

    4 Newall C, Anderson, LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals . London, England: Pharmaceutical Press; 1996.

    5 Norman JA, Pickford CJ, Sanders TW, et al. Human intake of arsenic and iodine from seaweed-based food supplements and health foods available in the UK. Food Addit Contam . 1987;5:103-109.

    6 Harrell BL, Rudolph AH. Kelp diet: a cause of acneiform eruption [letter]. Arch Dermatol . 1976;112:560.

    7 Walkiw O, Douglas DE. Health food supplements prepared from kelp—a source of elevated urinary arsenic [letter]. Can Med Assoc J . 1974;111:1301-1302.

    8 Walkiw O, Douglas DE. Health food supplements prepared from kelp—a source of elevated urinary arsenic. Clin Toxicol . 1975;8:325-331.

    9 Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant. 1998;13:526-527.

    Revision Information

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