What is 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.

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...

Safety Issues

Studies have found that levels of iodine vary widely among bladderwrack products. ² 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. ³ Finally, bladderwrack, like other sea plants, can concentrate toxic heavy metals, such as arsenic, from the surrounding sea water. ⁴ One report suggests that use of a bladderwrack product with a high heavy metal content is responsible for a case of kidney failure. ⁵ Heavy metals present particular risks for pregnant or nursing women, children, individuals with kidney disease, or anyone using...