IT was once harvested by hardy Hebridean fisherman from rocks in the sea and burned on the shore for raw materials and exported across the British Isles.
Now young women have been advised to take pills derived from Scottish seaweed after researchers concluded they can boost the production of vital chemicals in the body in as little as three days.
A study by scientists at Glasgow University has found that kelp extracted from wild wrack seaweed collected in Outer Hebrides raises low iodine levels in young women and is the equivalent to eating one-and-a-half whole mackerel a day.
Iodine deficiency is one of the main causes of an underactive thyroid, and is known to result in feelings of being run-down and lacking in energy. The condition has also been blamed for causing weight gain, aching muscles and brittle fingernails.
Even a mild lack of iodine during pregnancy can have an impact on children's development in the first nine years of life, leading researchers to say that iodine deficiency in pregnant women in the UK should be treated as an important public issue.
The Glasgow University study was based on 42 women aged 25, taking seaweed supplement capsules over a period of two weeks.
Before the trial, iodine consumption was far lower than the daily minimum recommended intake of 140 micrograms (mcg), while more than half of the group were found to be iodine insufficient.
At the end of the trial the group with low iodine levels showed a significant rise from 93 mcg of chemical present in their systems to each day to 262 mcg per day.
The report said: "Iodine-insufficiency is now a sustained issue in the UK and other European countries, due to low intakes of dairy and seafood, especially where iodine fortification is not in place.
"We tested commercially available encapsulated edible seaweed for its acceptability to consumers, iodine bioavailability and the impact of a two-week long daily supplementation on iodine levels and thyroid function among healthy non-pregnant women of childbearing age, self-reporting low dietary consumption of dairy products and seafood, with no history of thyroid or gastro-intestinal disease.
"The seaweed was an effective source of iodine among people with insufficient levels prior to the study."
Burning large quantities of seaweed produces iodine-rich soda ash, which was used in glass and soap production at the turn of the last century. It sustained a large industry on the Scottish Isles, but demand dried up when alternative sources of iodine were found.
Seaweed pills have become something of a fad in recent years, with celebrities such as Gwyneth Paltrow, Milla Jovovich and Oprah Winfrey all reported to be big fans of adding seaborne vegetation to their diet. But the study is the first time their health benefits have been confirmed.
A spokesman for Scottish herbalist Napiers, which was founded in 1860, said: "Our pure, wild organic seaweed is sustainably harvested from the clear waters off the remote conservation islands of the Outer Hebrides. This method of harvesting and drying is essential in preserving the ocean."
A spokesman from the Seaweed Health Foundation added: "As it is dried at low temperatures it regularly tests over 100 per cent higher in all vitamins and minerals tested than high-temperature dried, cheap commercial kelp."