This supplement may provide harmful amounts of iodine

In the pursuit of better health, many turn to dietary supplements. 

Among these are supplements and products made with seaweed and kelp. Several of these products claim to be a good source of the nutrient iodine.

Many people in Norway do not get enough iodine, and the Norwegian Institute of Public Health recommends iodine supplements for those who consume little milk, yoghurt, and white fish.

It may therefore seem logical to choose seaweed- and kelp-based supplements to increase iodine intake. But is that actually a good idea?

100 times more than the recommended dose

Inger Aakre researches nutrition at the Norwegian Institute of Marine Research. In 2021, she led a study examining iodine levels in seaweed and kelp products sold in Norway.

"Many of the products we analysed contained extremely high amounts of iodine. In the worst cases, a single dose or serving could provide more than 100 times the recommended daily intake," says Aakre. 

It was also difficult to find information about iodine content on the product labels.

"Only 24 out of 96 products listed iodine levels. And our testing showed that the declared values did not always match the actual iodine content," says Aakre. 

Can disrupt thyroid function

"Too much iodine is not good for the thyroid gland," says Sara Salehi Hammerstad, a specialist in endocrinology and internal medicine at Oslo University Hospital.

She explains that a healthy thyroid can adapt to an excessively high intake of iodine for a short period, meaning it will not affect the gland.

But she says that continuously consuming very large amounts of iodine can affect thyroid function.

"This can lead to low thyroid activity or it can trigger an overactive thyroid function," she says.

High thyroid activity can cause symptoms such as heart palpitations, weight loss, fatigue, and sleep problems. In some cases, medication is needed, says Hammerstad.

A 2020 study by the Institute of Marine Research investigated iodine status in people who regularly use seaweed- and kelp-based supplements and/or food ingredients.

The results suggest that this group has a high risk of iodine excess, writes the Norwegian Institute of Public Health.  

Hammerstad says that she has occasionally seen patients who developed thyroid disturbances after using seaweed and kelp supplements.

"But it usually doesn't produce extremely high values like we sometimes see with other conditions linked to high thyroid activity," says Hammerstad. "The condition is usually reversible, but in some individuals, high iodine intake can trigger autoimmune hyperthyroidism."

Recommends caution

Norwegian health authorities advise people to be cautious with seaweed and kelp products. The Norwegian Directorate of Health writes this on its website: 

'Because seaweed and kelp can contain harmful amounts of iodine, they should generally be used with caution.'

The Norwegian Food Safety Authority writes that until we know more, it may be best to avoid eating large amounts of seaweed and kelp.

This is how the Norwegian Food Safety Authority illustrates how much more iodine than recommended you may get from consuming certain products, especially those in powder form:

• A heaped tablespoon of dried sugar kelp contains 25,000 micrograms of iodine. 
• The recommended daily intake is 150 micrograms of iodine.

Sugar kelp is a type of brown algae. Researcher Inger Aakre explains that brown algae usually contain the highest levels of iodine. Red and green algae generally contain less.

Iodine levels can vary greatly between different types of algae. This creates new problems, says Aakre.

"We see poor labelling, incorrect labelling, and missing information about contents. Many products state which seaweed or kelp species is used instead of declaring the amount of iodine. That requires consumers to have an unrealistically high level of knowledge to make safe choices," she says.

Aakre believes that this places too much responsibility on the consumer.

"Follow the recommended dosage"

Endocrinologist Sara Salehi Hammerstad says you should be especially careful about using large amounts of seaweed and kelp supplements. 

"If you already have an overactive thyroid or thyroid condition, you are more at risk," she says.

She also points out that caution applies to all kinds of iodine supplements.

"If you take iodine in drop form or as tablets, it's also important to make sure you follow the nationally recommended dosage," she says.

New survey

Inger Aakre says that researchers at the Institute of Marine Research have started a new survey of iodine levels in seaweed and kelp products, commissioned by the European Food Safety Authority (EFSA).

"We are currently investigating new seaweed and kelp products in Norway and the Netherlands. We will analyse and assess the products for both iodine and heavy metals," says Aakre. 

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Translated by Alette Bjordal Gjellesvik

Read the Norwegian version of this article on forskning.no

Reference:

Aakre et al. Commercially available kelp and seaweed products – valuable iodine source or risk of excess intake?, Food & Nutrition Research, vol. 65, 2021. DOI: 10.29219/fnr.v65.7584

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