Fucus vesiculosus, known by the common name Bladder wrack, is a seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans, also known by the common names black tang, rockweed, bladder Fucus, sea oak, black tany, cut weed and rock wrack. It was the original source of iodine, discovered in 1811, and was used extensively to treat goitre, a swelling of the thyroid gland related to iodine deficiency. In the 1860s, it was claimed that bladder wrack, as a thyroid stimulant, could counter obesity by increasing the metabolic rate and, since then, it has been featured in numerous weight-loss remedies.
Fucus vesiculosus is one of the most common algae on the shores of the British Isles. It is recorded from the Atlantic shores of Europe, Northern Russia, the Baltic Sea, Greenland, Azores, Canary Islands, Morocco and Madeira On the Atlantic coast of North America from Ellesmere Island, Hudson Bay to North Carolina.
The large brown algae have similar life cycles. At maturity the reproductive bodies form in conceptacles sunken in receptacles produced towards the tips on the branches. In these conceptacles oogonia and antheridia are produced and after meiosis they are released. After fertilisation, the zygote develops, settles and grows to form the diploid sporophyte plant.
The large vegetative phase is diploid and gametophytic. Meiosis occurs during the formation of the gametes. The egg cells are formed on the female plants in conceptacles embedded in receptacles. The spermatozoids and egg cells are extruded from the conceptacles. Once fertilised, the zygote settles and grows to form the new diploid gametophyte.
A common food in Japan, bladder wrack is used as an additive and flavouring in various food products in Europe. Bladder wrack 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.
Primary chemical constituents of this plant include mucilage, algin, mannitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals. The main use of bladder wrack (and other types of seaweed) in herbal medicine is as a source of iodine, an essential nutrient for the thyroid gland. Bladder wrack has proved most useful in the treatment of underactive thyroid glands (hypothyroidism) and goitre. Through the regulation of thyroid function, there is an improvement in all the associated symptoms. It has a reputation in helping the relief of rheumatism and rheumatoid arthritis, both used internally and as an external application upon inflamed joints. A chemical constituent of bladder wrack 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 several over-the-counter preparations for heartburn. The same constituent gives bladder wrack laxative properties as well. Other proposed uses of bladder wrack include treating atherosclerosis and strengthening immunity, although there is no scientific evidence at present that it works for these purposes.
Bladder wrack should not be used in cases of hyperthyroidism or cardiac problems, or during pregnancy and lactation. Excessive dosage (many times the recommended dosage) may lead to hyperthyroidism, tremor, increased pulse rate and elevated blood pressure.