Dr Simon Faulkner and Dr Stefan Kraan

Discovered in 1811, iodine is a chemical element required by humans and animals for the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones are multifunctional and have important roles in the regulation of growth, development and metabolism. Iodine is therefore an essential trace element that affects almost every physiological process in the body.

9.4aquaculture seaweed

Although iodine can be obtained from a number of food sources, deficiency of the element is a common global problem and is considered to be the primary cause of impaired cognitive development in children by the World Health Organization.

Functions of iodine

Thyroid hormones increase basal metabolic rate which ultimately modifies the amount of energy used by humans and animals when at rest. An increase in iodine intake is associated with increased metabolism of proteins, fats and carbohydrates as well as heat production in the body. Another important function of the thyroid hormones 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 deficiency can cause irreversible damage to the foetal/new born brain during this period of development.

Iodine deficiency

A sufficient dietary intake of iodine is important as too much or too little can have a negative consequence on human health. Symptoms of excessive iodine intake can include high temperature, increased heart rate and excessive sweating. Iodine deficiency however is a much more common problem and can have profound effects on growth and development due to the inadequate production of thyroid hormones.

Symptoms of iodine deficiency include fatigue, congenital disorders, goitre, weight gain and altered body temperature. Goitre is a well-known, visible symptom of iodine deficiency, whereby the thyroid gland in the neck becomes swollen. This condition is also accompanied by increased appetite and weight loss.

Seaweed as a source of iodine

The World Health Organization recommends 150µg of iodine daily for adults depending on age and pregnancy status. In addition to eggs and dairy products, seafood such as shrimp, cod, tuna and in particular seaweed also represent excellent and healthy sources of iodine. Although iodine levels in seaweed vary widely between species, in general, seaweeds contain much more iodine than most – if not all ― other foods.

The high levels of iodine in seaweed can be explained by the oxidation of iodide to hypoiodous acid and molecular iodine by cell wall haloperoxidases. The oxidised iodine may then cross the plasmatic membrane and accumulate in seaweed tissues at levels 30,000 times as high as those in the surrounding seawater.

In certain brown seaweeds the level of iodine can be as high as 4.5% of dry weight and for this reason seaweeds 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.

Iodine derived from the Asian kelp species U. pinnatifida (Harvey) Suringar has been reported to inhibit tumourogenesis in rats with carcinogen-induced mammary tumours, although the exact mechanism of action has yet to be explained. One study has also suggested that the high seaweed-derived iodine content in their diet may account for the relatively low prevalence of breast cancer in Japanese women.

Additional benefits

Seaweed can help meet the recommended iodine intake by either direct consumption or by including it in the diet of animals used for human consumption. Either way, the end goal is to ensure that neither too much nor too little iodine is consumed in order to ensure an optimal healthy daily intake. Overall, incorporation of seaweed into our diet will not only improve health but will also facilitate sustainable food production.

Additional benefits of seaweed consumption by animals and humans also include the exceptionally high level of minerals, the presence of vitamins, antioxidants and a range of other bioactive compounds in the seaweed. The success of seaweed as a relatively new food and feed resource in Europe also requires increased consumer awareness concerning the health benefits of seaweed consumption.