Can there be too much of a good thing when it comes to iodine?

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This is a question we ask ourselves, and get asked, a fair bit. Since the subject invokes hot debate. We personally find ourselves often going over the recommended dosage of iodine per day. To date we haven't experienced any problems. However for the sake of argument, we thought we would gather research we’ve come across to present a balanced dialogue. 

The main takeaway is this; it all really depends on your individual circumstance. There is no one way to consume iodine. There are however guidelines to adopt and follow if you would like. It is also a matter of personal preference and a bit of good old experimentation, unless you are highly sensitive to iodine then it is best to keep the experimentation to a minimum.

As a species, we have been eating seaweed for an incredibly long time (1). We have become highly adaptable to fluctuations of nutrient intake. The forager Monica Wilde urges us to consider not what the average intake means to us, but what our individual intake could be (2). In this article we will be taking a look at what sort of Iodine intake is recommended for certain individuals.

Before we dive into the data, we’ll begin by looking at some key terms and definitions. 

What is an Intake recommendation for iodin I hear you ask? The Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) [2] have developed various calculations for recommended dosages of iodine and other nutrients known as Dietary Reference Intakes (DRIs). According to the NIH website, ‘DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people’. 

The following key terms (as listed on the NIH website) we will focus on today are:

Recommended Dietary Allowance (RDA): this is the ‘average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals’ (3).

Daily Value (DV): unit or percentage level of various nutrients in a standard serving of food

Adequate intake (AI):  Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA  (3)

Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects (3).

The FNB conducted a study in the US looking at recommended iodine intake per day for people of different ages. The table below shows their data. We can use this as a general rule of thumb.

So here we have clear indications of what is recommended by health organisations on an average scale. The FBN recommends 150 mcg for adults 19 and older as an average. Some people however may be more sensitive to iodine so the figure may be lower for these individuals.

We must also take into account the fact that each seaweed contains considerably different levels of naturally occurring iodine per gram (5). The level of iodine in seaweed will vary seasonally due to regional and global location, water temp and age of the plant (6).So depending on what you're eating, it’s important to factor this into your situation. 

In general though, the brown seaweeds (Phaeophyta) including kelp contain higher levels of iodine than the red and green seaweeds. Further to this, we can use the following data on ‘Nori’ as another handy guide.

Along with nori, the NIH (National institute of health) has developed a table of iodine content in select foods (3).

To explain the above, if the daily recommended intake for adults and children above 14 years old is 150 micrograms (as shown in table 1), then 5g of nori flakes would be 77% of the daily value for these individuals. 

Finally, let’s discuss the Tolerable upper intake level. This is the maximum daily intake that is unlikely to cause adverse health effects. Responses to excessive iodine will vary from person to person. For some, a recommended intake may be too high or even too low so it’s always good to see a physician if you need clear guidance on an individual level. 

Another important note when it comes to excessive iodine levels is the loss of iodine involved in the process from harvest to digestion and bioactivity. Once the fresh seaweed is harvested, the next stage of primary processing includes drying, boiling or freezing. It has been noted that either drying, or boiling seaweed in fresh water for a couple of minutes may reduce the iodine content (7). On top of that, only 49–82% of seaweed iodine appeared to be accessible for absorption by humans after gastrointestinal digestion (8). So even though data is available for iodine content in seaweed, there is much to break down with regards to what is actually available by the time it's made available to your body.

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Conclusion

To reiterate what we discussed before, the amount of iodine you can safely consume depends on circumstance. There is data available for recommended average intakes, but when it comes to an individual level there is less data to read. This is what you’ll need to find out for yourself. In our experience though it is best to start small and work your way up. Kelp in powdered / capsule form will be much more concentrated than seaweed flakes. Which is why we have developed our seaweed flakes to include a variety of species for a more balanced nutrition and mineral content. For those with an over-active or under-active thyroid, it's important to talk to your GP about the best way to include iodine in your diet. Seaweed can be a great way not only to ingest certain levels of iodine, but many more nutrients and minerals that benefit our body.