Sea vegetables and Iodine

What are sea vegetables?

Sea vegetables are marine plants which grow in our seas and oceans. These marine plants also named macro-algae are extremely diverse and are generally classified into three groups which include brown, green and red algae. Sea vegetables contain significant amounts of carbohydrates, proteins, lipids and vitamins which are all important nutrients. However, sea vegetables are perhaps best known for their high levels of macro-minerals and trace elements often exceeding the levels found in land vegetables by a factor of 10 or more.

Sea vegetables also contain a large number of unique bioactive compounds that provide health benefits which go beyond satisfying traditional nutrient requirements. For this reason, sea vegetables are now being used as functional ingredients for human food applications. In total, there are over 10,000 species of macro-algae of which over 600 of these species can be found in Ireland. It is important to note that each seaweed species has a unique composition.

In addition to minerals and trace elements, additional bioactive compounds found in sea vegetables include unique polysaccharides (Fucoidan, Alginates, Laminarins, Agar, Ulvans), proteins, peptide and amino acids, fatty acids (including Omega-3) and pigments (e.g. fucoxanthin).



Sea vegetables used by Five Sciences

The sea vegetables used in our products are harvested, principally from the clear, clean west coast of Ireland. All of our sources are organically certified (EU) and harvested in a sustainable manner.

For example, Fucus vesiculosus (‘Bladderwrack’) is sustainably harvested by cutting the plant while leaving a proportion of the plant to regenerate. This ensures that that the lower part of the plant and holdfast are left attached in order to facilitate regeneration.

Fucus vesiculosus is a green/brown colour but is often dark green when dried. Bladderwrack contains a number of minerals including iodine, calcium, magnesium, potassium, sodium and some water-soluble vitamins and it is also an excellent source of fucoidan. Fucus vesiculosus is one of the most common intertidal macro-algae along the Irish shoreline. It is present in both exposed and sheltered habits, often together with the familiar seaweed Ascophyllum nodosum.

Fucus vesiculosus grows up to around 80 cm in length, has a short stipe and a wavy-edged frond, paired branched with a prominent mid-rib. This sea vegetable also has oval gas-filled bladders, which provide buoyancy to float the sea vegetable towards the sunlight thus facilitating photosynthesis. In comparison, Kelps such as Laminaria digitata can commonly grow to lengths of 2-3 metres and has large, long, flat, finger-like fronds with a smooth rubbery/leathery appearance.

Sea vegetables as a source of iodine:

The World Health Organization recommends 150µg of iodine daily for adults; however, this requirement varies depending on age and pregnancy status. In addition to eggs and dairy products, seafood such as shrimp, cod, tuna and in particular sea vegetables also represent an excellent and healthy source of iodine. Although the level of iodine in sea vegetables varies greatly between species, in general, sea vegetables contain much more iodine than most – if not all – other foods on a dry weight basis.

In certain brown sea vegetables, the level of iodine can be as high as 4.5% of dry weight and for this reason sea vegetables such as Kombu (Saccharina japonica) have been consumed in China, Japan and Korea for centuries as a dietary iodine supplement to prevent goitre and promote good health. Most of the Kombu is dried and eaten directly in soups, salads and tea, or used to make secondary products with various seasonings.

What is Iodine?

Discovered in 1811, iodine is a chemical element required for the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These thyroid hormones are multifunctional and have important roles in the regulation of growth, development and metabolism. Iodine, therefore, is an essential trace element as it affects almost every physiological process in the body. Although iodine can be obtained from a number of food sources albeit in various quantities, deficiency of the element is a common global problem and is currently considered to be the primary cause of impaired cognitive development in children by the World Health Organization1.

Importance and Functions of iodine:

The uptake of dietary iodine by the human and animal thyroid glands leads to the production of thyroid hormones and is a well-established phenomenon. These hormones increase basal metabolic rate which ultimately modifies the amount of energy used when at rest. An increase in iodine intake is associated with increased metabolism of proteins, fats and carbohydrates and also increases heat production in the body. Another important function of the thyroid hormones and, by inference, iodine is to maintain healthy brain development. For instance, in the human foetus, brain development commences during late pregnancy and is dependent on adequate production of thyroid hormones.

Iodine – interesting facts:

  • A sufficient dietary intake of iodine is important as too much or too little of the element can have a negative consequence on human health. For example, symptoms of excessive iodine intake can include high temperature, increased heart rate and excessive sweating.
  • However, iodine deficiency is a much more common problem and can have profound effects on growth and development due to the inadequate production of thyroid hormones. Iodine deficiency is one of the three key micronutrient deficiencies highlighted as major public health issues by the World Health Organisation2.
  • In 2010, a scientific paper was published estimating that 50% of Europeans do not consume sufficient iodine as part of their daily diet. Another study conducted in 2015 reported that 39% of schoolgirls surveyed in Northern Ireland are Iodine-deficient and this agrees with a previous UK-based study which found that 68% of UK schoolgirls are iodine-deficient3,4,5.
  • In the UK and Ireland specifically, there is growing evidence that pregnant women do not consume sufficient iodine3,6,7which is of particular concern as an insufficient iodine intake is associated with impaired cognitive development of the offspring8.
  • The cost of iodine deficiency both in terms of healthcare and work-based productivity was recognised in Europe a long time ago. For example, in 1993 the cost of iodine deficiency in Germany alone was in excess of 1 billion dollars9.
  • Symptoms of iodine deficiency include fatigue, congenital disorders, goitre and altered body temperature. Goitre is a well-known, visible symptom of iodine deficiency, during which the thyroid gland in the neck becomes swollen.
  • A number of studies in animals and humans have shown that iodine (from sea vegetables or other sources) may protect against cancer10,11,12.
  • Iodine derived from brown sea vegetables has been reported to inhibit tumourogenesis in rats with carcinogen-induced mammary tumours, although the exact mechanism of action has yet to be elucidated13.
  • The ability of iodine or iodine-rich sea vegetables to inhibit tumour development is reinforced by the relatively low rate of breast cancer in Japanese women who consume an iodine-rich (sea vegetable-rich) diet14.


  1. World health organisation (WHO)
  2. Hernández, M.D.C.V., Kyle, J., Allan, J., Allerhand, M., Clark, H., Manieg, S.M., Royle, N.A., Gow, A.J., Pattie, A., Corley, J. and Bastin, M.E., 2017. Dietary iodine exposure and brain structures and cognition in older people. Exploratory analysis in the Lothian Birth Cohort 1936. The journal of nutrition, health & aging, 21(9), pp.971-979.
  3. Zimmermann, Michael B. “Symposium on ‘Geographical and geological influences on nutrition’Iodine deficiency in industrialised countries.” Proceedings of the Nutrition Society 69.01 (2010): 133-143.)
  4. Lazarus, John H. “Iodine status in Europe in 2014.” European thyroid journal 3.1 (2014): 3-6.
  5. McMullan, P. A., et al. “A cross-sectional survey to determine iodine status of school girls living in Northern Ireland.” Age (years) 14 (2015): 15.
  6. Bath, Sarah C., et al. “Iodine intake and status of UK women of childbearing age recruited at the University of Surrey in the winter.” British Journal of Nutrition10 (2014a): 1715-1723.
  7. Bath, Sarah C., et al. “Iodine deficiency in pregnant women living in the South East of the UK: the influence of diet and nutritional supplements on iodine status.” British Journal of Nutrition 111.09 (2014b): 1622-1631.
  8. Hynes, Kristen L., et al. “Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort.” The Journal of Clinical Endocrinology & Metabolism 98.5 (2013): 1954-1962.
  9. Gutekunst R. Iodine deficiency costs Germany over one billion dollars per year. IDD Newsletter 1993;9:29-31.
  10. Cann, Stephen A., Johannes P. van Netten, and Christiaan van Netten. “Hypothesis: iodine, selenium and the development of breast cancer.” Cancer Causes & Control 11.2 (2000): 121-127.
  11. Eskin, Bernard A. “Iodine and mammary cancer.” Adv Exp Med Biol 91 (1977): 293-304.
  12. García-Solís, Pablo, et al. “Inhibition of N-methyl-N-nitrosourea-induced mammary carcinogenesis by molecular iodine (I 2) but not by iodide (I−) treatment: Evidence that I2 prevents cancer promotion.” Molecular and cellular endocrinology 236.1 (2005): 49-57.
  13. Funahashi, Hiroomi, et al. “Wakame Seaweed Suppresses the Proliferation of 7, 12‐Dimethylbenz (a)‐anthracene‐induced Mammary Tumors in Rats.” Cancer Science 90.9 (1999): 922-927.
  14. Smyth, P. P. “The thyroid, iodine and breast cancer.” Breast Cancer Research 5.5 (2003): 235-238.