Bladderwrack

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. The main use of Bladderwrack and other types of seaweed in herbal medicine is as a source of iodine, an essential nutrient for the thyroid gland.

Because Bladderwrack contains high concentrations of iodine, it is sometimes recommended as a treatment for hypothyroidism (underactive thyroid gland). 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. 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. Other proposed uses of Bladderwrack include treating atherosclerosis and strengthening immunity, although there is no real evidence at present that it works for these purposes.

Because of safety concerns (see Safety Issues below), we do not recommend the use of Bladderwrack.

Studies have found that levels of iodine vary widely among Bladderwrack products, even including the raw form of the herb. Because of this, there is an unacceptable risk of overdosing on iodine and causing hyper- or hypothyroidism. Bladderwrack and other seaweed preparations can worsen acne and decrease iron absorption. Finally, Bladderwrack like other sea plants, can concentrate toxic heavy metals such as arsenic from the surrounding sea water. One report suggests that use of a Bladderwrack product with a high heavy metal content is responsible for a case of kidney failure. Heavy metals present particular risks for pregnant or nursing women, children, individuals with kidney disease, or anyone using Bladderwrack long term or in high doses.