Iodine in Common Edible Wild NZ Seaweeds – An Alternative to Iodized Salt!

Iodine content of New Zealand’s Common Edible Wild Seaweeds, for (low-sodium) adequate iodine intake

This article documents the amount of edible seaweeds commonly found on NZ’s shores, that adults can rely on as their exclusive source of iodine, in replacement for iodized salt. Why would anyone drop salt? That you will get a hint in the second part “The Story” but first…the facts!

It took me so much time to compile all this info together, so today is a very exciting day, finally putting this out for everyone to enjoy 🙂 Here’s the menu, and I wish you a lot of fun in foraging, and a healthy long happy life away from the unnecessary pains of hypertension! Later (in a future post hopefully) I will tell you the story of why I gave up salt completely, and how to achieve that in just about 3 months painlessly. But this post for now is more about the “how” part of staying away from salt.

This article is a work in progress. Since I am starting to have a set of actionable data, I am sharing so you can enjoy it as well.


2 SUMMARY

PART 1/2 – THE FACTS
Things to know beforehand to use the facts intelligently
Safety precautions
Seaweed preparation
Bio-variations
Absorbability
Units
References

Seaweeds Iodine/Sodium contents and daily intake

SEAWEEDS WITH LOW IODINE (FOR EATING)
– Long sea lettuce – Ulva stenophylla
– Nori – Porphyra species– Karengo (Maori)
– Wakame – Undaria pinnatifida
– Bull Kelp – Durvillaea antarctica – Rimurapa/Rimuroa

SEAWEEDS WITH HIGH IODINE (FOR SEASONING)
– Neptune’s necklace – Hormosira  banksii
– Bladder kelp – Macrocystis pyrifera – Rimurimu
– Paddle weed – Ecklonia radiata

Methods of calculation

PART 2/2 – THE STORY (of how you are bound to come to seaweeds to replace iodized salt)

Sources


 

Part 1/2: THE FACTS

Things to know beforehand to use the facts intelligently

Safety precautions

The seaweeds below are found virtually everywhere on New Zealand coasts, if one is not, another will. There is no need to go specifically to the sites listed below, those are just sites chosen by the scientists for their own reasons. In any case, do your foraging safety homework first: always have a buddy, never pull but instead cut live seaweeds so they can regrow, watch your steps to avoid sea snails on rocks, small stand-alone rocks/boulders can are not stable even if they’re big and heavy, no stream pouring nearby, no industries and boating activity nearby, no sewage discharge nearby…I can’t be thorough here on these.

Basically, this article is not a thorough coastal foraging guide. There are some specific things you may want to know for different aspects of safety, other things you may want to know to minimize your impact on the intertidal biodiversity, some sites may be tapu (considered sacred by Māori) and better left alone, etc. All I do here is document the iodine/sodium content of a few common edibles.

Also, this article focuses on iodine requirement for adults. If you need the seaweed numbers for children or adolescents contact me, I’ll be happy computing them and updating this article for you.

Seaweed preparation

The quantities below only apply to cleaned and dried seaweeds, not to wet seaweeds: not drained, not seaweeds that feel dry-ish to the touch. By dried I mean something you put effort into drying: crispy-dry if thin seaweeds or corn-chips-cracky/dry if thick just to be very clear. The cleaning to reduce salt content consists in soaking in freshwater (non-salty) baths with several water changes.

Bio-variations

Seaweeds are known to show some variation in their characteristics like nutrient content, between species even closely related ones, based on the micro-ecosystem, weather, seasons, etc…In fact this applies to all plants, but people tend to be used to the idea that all foods contain exactly what the nutritional facts state. They don’t, those are averages and estimates from ranges that sometimes are very wide! This being said, some of these seaweeds  have been measured in different places of a coherent geographic area (NZ) and at different times of the year. Also, the ranges of iodine are generally always in the same narrow range, most often.

Absorbability

Different seaweeds have different “iodine species” (different molecules that contains iodine) and they are not digested the same. So it’s difficult to know how much iodine is absorbable exactly from seaweeds in general, let alone variations among people etc. This article assumes all iodine in the plant is absorbed, it may not be the case, but this assumption provides a additional margin of safety to stay clear from excess. As for staying of deficiency, minimum iodine requirements are likely to be met at doses between the recommended daily value and the tolerable upper limit. Both will be provided.

Units

The unit below will be “mcg / g” means microgram per gram. I prefer this unit for iodine because daily requirements are expressed in micrograms and grams are something people can measure in their kitchen. This unit is the same as “mg / kg” (milligram per kilogram) or “ppm” (parts per million).

References

The little number between brackets (i.e. [1] or [5]) is to direct to the source of that information, listed below in Sources.

Seaweeds Iodine/Sodium contents and daily intake

If you found in the literature, or measured in your lab other values from these for LOCALLY HARVESTED/FARMED (in New Zealand) seaweeds named below, please comment the sources or drop me an email and I’ll get in touch with you to ask for the more info to update this article.

SEAWEEDS WITH LOW IODINE (FOR EATING)


 

Long sea lettuce – Ulva stenophylla – (Maori name?)

1_Ulva-stenophylla

Image credits: Photo: Algaebase;
Illustration: Setchell and Gardner, 1920b

More info: http://www.marinelife.ac.nz/species/1052
Note: Ulva stenophylla is a specific species of Ulva (sea lettuces). Data provided may be different for other Ulva. To illustrate that, for instance Ulva stenophylla was found to have double the protein of Ulva lactuca [1], another sea lettuce. Nothing guarantees all Ulva have the same nutritional profile.

Wild samples (3): 27 ±12 mcg/g [1]
The adult DRI of 150 mcg/day is attained with: ~10g (washed, dried, sodium: ~20mg)
The NZ Tolerable upper Limit is attained with: ~35g (washed, dried, sodium: ~55mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

Wild samples (3):
Onehunga Bay, Auckland April 2004
Onehunga Bay, Auckland April 2004
Onehunga Bay, Auckland August 2004


 

Nori – Porphyra species – Karengo (Maori)

Nori – Porphyra species – Karengo (Maori)

Image credits: (left) Kim Westerskov;
(right) Wendy Nelson, NIWA

More info: http://www.marinelife.ac.nz/species/990
Wild samples (3): 64 ±21 mcg/g [1]
Commercial sample (1): 45.03 mcg/g [1] (within range of wild)

DRI for iodine (150 mcg/day) is attained with: ~4g (washed, dried, sodium: ~6mg)
TUL for iodine (1100 mcg/day) is attained with: ~13g (washed, dried, sodium: ~22mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

Wild samples (3):
Nelson May-October 2004 (3)

Commercial sample (1):
Kaikoura Coast 2004


 

Wakame – Undaria pinnatifida – (not a native plant => no Maori name)

Wakame – Undaria pinnatifida

Image credits: © Jon Sullivan
Image cropped from original..
Cc by nc small some rights reserved

More info: http://www.marinelife.ac.nz/species/1053
Wild samples (3): 171 ±28 mcg/g [1]
Commercial sample (1): 100.67 mcg/g [1] (close to range of wild)

DRI for iodine (150 mcg/day) is attained with: ~1g (washed, dried, sodium: ~40mg)
TUL for iodine (1100 mcg/day) is attained with: ~5g (washed, dried, sodium: ~200mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

Wild samples (3):
Nelson, April–September 2004 (3)

Commercial sample (1):
Wellington Harbour, 2004


 

Bull Kelp – Durvillaea antarctica – Rimurapa/Rimuroa (Maori)

Bull Kelp – Durvillaea antarctica - Rimurapa/Rimuroa (Maori)

Image credits: © lupra, all rights reserved

More info: http://www.marinelife.ac.nz/species/808
Wild samples (3): 291.9 ±270 mcg/g [1]

This seaweed has a very wide variation of iodine content. Only a tolerable upper limit can be given for the worst-case scenario.
That amount which should be safe in terms of avoiding excess can be in certain cases too low to meet daiy recommended value. This seaweed is safe for occasional seasoning, but not recommended to rely on safely as one’s daily only source of iodine.
TUL for iodine (1100 mcg/day) is attained with *potentially*: ~2g (washed, dried, sodium: ~100mg)

Wild samples (3):
Piha, Auckland, NZ , April 2004 (2)
Maori Bay, Auckland, NZ, in August 2004 (1)


 

SEAWEEDS WITH HIGH IODINE (FOR SEASONING)

Use only as seasoning: from the same way most people sprinkle salt or pepper, to rather the way toddlers would sprinkle super hot chilli pepper in their food 🙂


 

Neptune’s necklace – Hormosira  banksii  – (Maori name?)

Neptune's necklace - Hormosira banksii

Image credits: © Melissa Hutchison
Image cropped and levels adjusted from original..
Cc by nc small some rights reserved

More info: http://www.marinelife.ac.nz/species/862
Wild samples (3) : 1041 ±292 mcg/g [1]

DRI for iodine (150 mcg/day) is attained with: ~0,2g (washed, dried, sodium: ~10mg)
TUL for iodine (1100 mcg/day) is attained with: ~0,8g (washed, dried, sodium: ~50mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

If you do not have a microgram scale, to visualise how much that is, start from a large amount that your scale can measure (i.e. 10g) and divide the pile of seaweed just visually and with your hands, until you divide enough to reach those values. Divide 10g ÷ 2 =5g, ÷5 =>1g, ÷5 => 0.2g, *4 = 0.8g

Wild samples (3):
Piha, Auckland April 2004
Ti Point, Leigh April 2004
Beaumont, Auckland August 2004


 

Bladder kelp – Macrocystis pyrifera – Rimurimu (Maori)

Bladder kelp – Macrocystis pyrifera – Rimurimu (Maori)

Image credits: © Sue Mcgaw
Image cropped from original.
Cc by nc small some rights reserved

More info: http://www.marinelife.ac.nz/species/894
Iodine concentrations reported:
2115.81 mcg/g* [1]

DRI for iodine (150 mcg/day) is attained with: ~0,07g (washed, dried, sodium: ~3mg)
TUL for iodine (1100 mcg/day) is attained with: ~0,5g (washed, dried, sodium: ~20mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

* Commercial sample (1):
Tory Channel, near Nelson, NZ, 2003. (Sold as “kelp pepper”)


 

Paddle Weed – Ecklonia radiata – (Maori name?)

Paddle Weed – Ecklonia radiata

More info: http://www.marinelife.ac.nz/species/811

Wild samples (4): 3990 ±242 mcg/g [1]
Commercial samples (1): 3719.45 mcg/g [1] (within range of wild)

DRI for iodine (150 mcg/day) is attained with: ~0,04g (washed, dried, sodium: ~1mg)
TUL for iodine (1100 mcg/day) is attained with: ~0,25g (washed, dried, sodium: ~8mg)
(DRI = Daily Recommended Intake, TUL = Tolerable Upper Limit, defined by NZ, as of 2010)

You need a microgram scale if you want to visualize these amounts.

Wild samples (4):
Maori Bay, Auckland April 2004
Matheson Bay, Auckland April 2004
Beaumont, Auckland August 2004
Takapuna, Auckland August 2004

Commercial sample (1):
Wairarapa Coast 2004


 

Methods of calculation

Detail of the method used for calculating amounts of seaweed to attain adult DRI or TUL:
For DRI, the worst-case scenario is when the wild seaweed has the lowest possible average concentration.
This is because you want to have at least the DRI, so even the lowest concentration (in theory*) meets the needs.
Worst-case iodine concentration = Average of wild <minus> standard error (the number after ±)

For TUL, the worst-case scenario is when the wild seaweed has the highest possible average concentration.
This is because you want to not exceed the upper limit, so even the highest concentration (in theory*) meets the needs.
Worst-case iodine concentration = Average of wild <plus> standard error (the number after ±)

Then divide UL or DRI by worst-case concentration => How much covers the needs.

The sodium estimations are obtained in the following way: Average sodium concentration for that species <multiplied by> amount to meet DRI or TUL. The sodium quantities have their own standard error (small variations) but since the sodium amounts are extremely very low, high precision is irrelevant.

* There is no guarantee that seaweeds you may forage will match these number. They are quite likely too, but also may no. That means you can get “worse” with what you forage than my worst case-scenarios. Realistically, since people eat seaweed without caring at all to begin with, the guidelines and maximum edible amounts are very useful and far less risky than eating with no guideline.


 

Part 2/2 – THE STORY

Seaweeds are like Rome, all roads lead to them. I love to forage, to try new things in the kitchen, to try plant foods I never had, and to make sure people have the nutrients and health they need. These are some of many avenues where my insatiable curiosity roams to play, and each of them separately took me to seaweeds, like by enchantment. Can you imagine how fulfilling it can be walking by the beach and just snapping photos of seaweeds and intertidal species, going to the library to find books with pictures, learning to recognize, and then be foraging, preparing, something delicious and which takes an important place in nutrition? As fulfilling as falling in love for the first time. That is what life is all about, and I have yet a new lover. This time it is seaweeds!

Since transitioning to whole-food eating for evident health reasons, my partner and I no longer consume salt at home, like, interestingly, millions of other land-bound animal species that do very well without a salt shaker. Yes folks, sodium is of vital importance. What you may not know is that all the vital sodium you need, and far more than you need, is in all sorts of plant foods you eat, but we’ll keep the detailed story for another day, subscribe the RSS if you want to keep posted on new posts. Anyhow, since something as harmful as salt had been chosen as a vehicle for iodine fortification: if you skip the salt, you also skip the iodine, at least in iodine depleted soils like in New Zealand.
So we had three or really two choices:

  1. Replace the salt shaker by some sort of iodine supplement (in cooking, or as a tablet) but we had lost the salt shaker reflex and it is weird taking a pill each breakfast. You see, a cherry-flavoured vitamin B12 that melts in the mouth, once a week, is not a problem, but an iodine drug-like pill everyday, in a pill box and had with a glass of water, not for us…too medication-like.
  2. Rely on eating sea-animals (fishes, mollusks, etc…) but there’s a major problem with that.
    Recently, we fixed an urgently needed upgrade in our frankly standard and deficient knowledge on animal exploitation and the pressing issues related. Watch these documentaries Earthlings, Seaspiracy, Cowspiracy, to get a better idea what made us a bit less less ignorant on rather very important things. Anyway we decided it made complete sense to stay clear of intentionally killing/exploiting animals and better to instead just leave them alone along with the ecosystems they live in => Everything but sea animals, not even an option.
  3. Simpler, tastier, and far more fun: Learn to forage seaweeds! Go have a fun walk on the beach regularly, forage seaweeds and eat the right amount regularly. Use the right ones as a food and the right ones as a pepper (to sprinkle in small amounts).

Option #3 is very appealing now 🙂

Before that, my first approach was “iodine supplementation only” as can be appreciated in this article.  I was quite wary of variations in iodine content of seaweeds, some of which are enormous, and I did not want to take the risk. Having learned a bit more about seaweeds since that article, and a bit more about iodine acceptable intakes, I feel safe dropping the iodine supplement and relying more on locally foraged seaweeds. A decision like this is not done lightly and required good hands-on and knowledge on a few things:

  • knowing iodine concentrations in local seaweeds locally documented (so basically not something you read about “kombu” or “kelp” in general as a product, but science journals publishing iodine levels in clearly named and specific seaweed species harvested locally). That’s the only thing this article will help with.
  • a good ability to recognize exactly those species when foraging (not too hard but must be learned and practiced)
  • foraging safety (i.e. foraging fresh seaweeds instead of decaying ones, away from sources of pollution such as manufactures, landfills, sewage …)
  • nutritional awareness (safe levels of iodine).

Sources

[1] JL Smith , G Summers & R Wong (2010) Nutrient and heavy metal content of edible seaweeds in New Zealand, New Zealand Journal of Crop and Horticultural Science, 38:1, 19-28, DOI: 10.1080/01140671003619290

[Iodine] Can we safely get all our iodine only from seaweeds? A practical exploration

 This article is now considered “somewhat obsolete”. Basically, this article studied only the seaweeds that are commercially available, and did not explore the realm of locally (NZ) foraged seaweeds. I have since turned to carefully-selected, locally-foraged seaweeds, which seem to allow safe iodine intake: Iodine in Common Edible Wild NZ Seaweeds – An Alternative to Iodized Salt!


Are you vegan? or on a low-salt diet? or heading there? Then this will be relevant to you. The question of satisfying iodine needs through seaweed is not new as you will read in the history but below. I ask here a specific and very practical question:

Based on published science, can we or not safely rely entirely on seaweeds for iodine intake? If so, which ones? why so? and what to do in practice to implement that?

That is usually my approach, very practical, and I do heavily rely on the work of people that are very focused on non-practical aspects. To figure out the answer, we will have to define what is safe? what is reliable? Since the history of iodine deficiency is frankly quite fascinating, I will start with that, and then get more specifically into the seaweeds talk.

Part One – A quick (recent and epic) history of iodine deficiency

19th/20th century

Already in 1813, following the discovery that seaweeds have iodine, a Swiss physician postulated that seaweeds consumption could reverse goiter just like another sea product which the Greeks used for goiter: marine sponges in topical use. [1]

From 1813, it took no less than a century, for iodine to start reaching our diets, through salt iodization. And there are still problems. The Salt Institute declares “In 1990, only about 20% of the world’s households had access to iodized salt and were protected against Iodine Deficiency Disorders. After a major push, access now exceeds 70%”.[2] It will always fascinate me how slowly are accepted and spread undeniably effective solutions to major medical problems.

21st century – The ironic re-emergence of iodine deficiencies, “for health reasons”

While many countries are still working on making iodized salt the norm, other countries such as New Zealand (and probably others) are already experiencing the next iodine problem, a re-emergence of iodine deficiency [3]. Why? Several reasons, mainly health-driven:

1. People cutting on (iodized) salt to reduce cardiovascular “accidents” [3]

As salt awareness is growing, people do try to cut on visible salt. They do when using the shaker and in the kitchen. If that salt was iodized, cutting on salt also means cutting on iodine.
Automatically then, your only source of iodine becomes uncontrolled and random, with the execption of New Zealand* which I will develop later. When there is no more iodized salt in your diet, you rely almost entirely on the salt chosen by restaurants and food makers you eat, from the sea products you eat, on the (usually low) iodine content of the soil that grows your food, and even more rarely on the voluntary use of iodized salt in the supermarket food, the last industry I’d expect to care unless forced by law* or consumer trends.
*In New Zealand, bread manufacturers have been forced by law to iodize the salt in bread, since people still eat a lot of bread. Think of bread as a last refuge for salt. Once you got rid of table and cooking salt, the next thing to get rid of is either bread or the salt in it. Inevitably, when that happens, iodine deficiency will become a problem again. Salt being something unnecessary and unhealthy, should not be the carrier for iodine, or anything else that is important for health.

2. People switching to rock salts (i.e. Himalayan salts)

A pink rock salt recently gone quite mainstream, Himalayan salts mined and therefore usually very low in iodine by default. Although any amount of salt is not necessary and therefore contributing to a more unlhealthy status, Himalayan salt has gained popularity as a “healthier salt” due to claims of it containing a wide spectrum of trace minerals. Besides safety issues with the uncontrolled variation of the trace minerals, and a possible content of heavy metals, Hymalayan salts in the “natural” state do not contain a relevant amount of iodine and pose an (ironic) issue of iodine deficiency. In passing, the concept of “healthy salt” reminds me of the $30 million of US taxpayers money spent in 1967 by the National Cancer Institute to create a “safer cigarette”.

3. A rise of vegetarian and vegan diets

In studies done on iodine deficiency, vegans and vegetarians are mentioned as being at particular risk of iodine deficiency. The reason is that most seafood in the Western diet is animal-based, and that most animal produce (meat, milk, cheese) comes from animals that were given a feed artificially supplemented, either for the animal’s own health, as a means of supplementing the final product, or accidentally like in the case of milk-based iodine which comes (or used to come) from iodine containing disinfectants like Betadine applied on cow tits. [4] Other disinfectants have gradually replaced the iodine-based ones, resulting in lower iodine in cow’s milk.

4. The still-existing lack of a holistic agricultural practice

Some posters on the internet, widely shared, claim certain plant foods as reliable sources of iodine. It is not true because it depends heavily on the iodine content of the soil where the plant came from. A potato may be able to accumulate iodine, but since most soils are iodine-deficient, how much iodine should we expect in potatoes? Deficient soils are still far from being thoroughly and routinely balanced with life-sustaining elements, iodine being one of many. In fact, there is more thought being put in supplementing cows and their feed than in conditioning soils for the healthiest feed of humans: plants, fungi, and other non-animal foods. Most fertilization is still entirely focused at productivity and profitability, what is not? Yet we still buy produce based on weight, price, and appearance, not enough based on nutritional content or  taste, let alone environmental and social factors. There is however a growing culture of a holistic approach, aiming at going back to basics: taking pride in actually feeding people [5]. Iodine deficiency could likely be resolved by means of fertilization and cultivation methods, among other deficiencies.Picture 103

Image credits: Alena Kumpta Watercolor Art

Part Two – The search for the perfect seaweed

Criteria to match in order for a reliable, safe, and practical intake of iodine from seaweed only:

  1. Reliably narrow range of iodine concentration, so that we know accurately enough how much iodine is contained in let’s say a spoon or 10g.
  2. The range starts away from zero iodine (so that there is no risk of getting close to none)
  3. Practical concentration: the daily requirement ideally fits in more than a pinch, but less than a lot of tablespoons, so ideally something like a gram or a teaspoon, not one kilogram of seaweed because that would not be realistic nor practical.
  4. The seaweed has long history of usage and is generally safe
  5. The seaweed is easy to source
  6. High absorbability by human digestion
  7. Low heavy metal content

Hypothesises/Assumptions:

  1. The range of suitable iodine for human consumption is based on official recommendations : ~160 µg/day (upper limit UL or maximum: 1,100 µg/day)
  2. That official recommendation are correct is subject to debate, and here too. Official recommendations have changed a lot historically [1]
  3. OBJECTIVE: So rounding up, we will consider safe the range 150 ~ 1,000 µg/day, remember this.

Seaweeds – Variation in content of iodine

Given the large number of seaweeds in existence, the focus was intentionally restricted to a popular few:

  1. WakameUndaria pinnatifida (the fronds are called wakame, the base part of the same plant is called mekabu)
  2. KombuLaminaria digita japonica, also known as kelp
  3. Nori – which is tricky because it’s a whole genus (Porphyra genus) contaning many species including Laver (Porphyra umbilicalis) or Karengo (Porphyra columbina) and many others. Many seaweeds fall under nori.

These are the ranges in parts per million (ppm) or equivalent units :  mg/kg or µg/g (same as mcg/g or micrgrams per gram), all units reflecting the content as packed, usually dry [6,7] For iodine in seaweeds, the microgram per gram unit because the dietary recommendations for iodine are given in micrograms, and one gram of dry seaweed is human sized; if dried it would fit in a hand or a spoon.

  1. Wakame: 39 ~ 1,571 µg/g
  2. Kombu: 25 ~ 12,000 µg/g with one measured at 21,000 [8] by EU food safety authorities
  3. Nori: 0,7 ~ 550 µg/g

How absorbable is iodine from seaweed?

While iodine is an atom, its presence in food can exist in different forms, different molecules or ions referred to as “chemical species”. It’s important to know the chemical species of in foods because that affects bio-availability (how much we can absorb and use) or things like toxicity (less of a concern here).
A study published in 2005 compared kombu  to wakame concluded that kombu’s higher content of iodide made it a more bio-available choice than wakame’s various iodine species (monoiodotyrosine and diiodotyrosine) [9]

Heavy Metals Warning

Seaweeds are notorious for accumulating heavy metals. Interesting work was done by the Health Ranger, a food activist, on a very narrow but US-popular range of seaweeds. One brand of seaweeds harvested in New Zealand showed the cleanest profile in terms of heavy metals. Be careful though when chosing “New Zealand” as a reliable criteria for clean seaweed. The mention “from New Zealand”. All inhabited land in our day dumps pollutants in the sea, New Zealand is no exception, far from the common eco-fantasy. That is why, the cleanest New Zealand seaweeds are most likely harvested in open sea far from the land, ideally South towards Antarctica, in regions far from volcanic/human activity. In my survey ofseaweeds from shops, also saw “NZ-nori”, NZ-seaweed” and other “NZ” prefixed labels in large print. That could just be marketing to write NZ somewhere capitalizing on the good perceived image of New Zealand seaweed. It could also mean the product sold is the NZ species of a certain seaweed, but that by no means guarantees it was grown or harvested in New Zealand, or in clean waters.

Best seaweed verdict

Kombu: too much iodine, extremely wide range, and starts close to zero. It’s out.
Nori: wide range, start close to zero. It’s out.
Wakame: relatively narrow range (good) but starts close to zero. It’s out.

Among these three popular seaweeds I cannot see any candidate for a best seaweed taken daily on its own as the one and only source of dietary iodine. The fantasy of getting all iodine in precise amounts from seaweed alone is over for me. So what to do now?

Well, there is good news. There are other more viable avenues.

The solution: Get your iodine from more reliable sources than seaweeds

The natural way, and its limitations

  • Do not rely only on daily seaweeds unless it passes the above-discussed criteria/checklist
  • If relying partly on seaweeds, only consume a safe amount based on the method here: trusting observed ranges more than nutritional facts (generally one-shot, or copied off the net rather than measured) and always calculate to avoid the worst case scenario of toxic doses
  • If you forage, that’s wonderful. Do it intelligently though:
    • Select a clean foraging spot: Learn about the history of activity and pollution of the area you forage in.
    • Identify: Always identify the species you collect.
    • Quantify: Once you know the name of what you forage, look into the research to quantify the amount of iodine in different parts of plant.
  •  Research iodine ranges of other seaweed species (dulse, arame, …) <== and of course write me an email to show me what you found 😉

Relying on iodized salts/products

  • People with a very low-salt diet, and no other iodine source may choose a highly-iodized salt, that provides enough iodine in a very small daily intake of salt. That means a higher concentration than in normal salt. Note that iodized salts in general have by law wide ranges of allowed iodine (45±20 µg/g for NZ/Aus.). I read some research showing that the legal (already wide) ranges are not generally not respected and that an even wider range of iodine is actualy found in iodized salt products. This makes iodized salt an unreliable source of iodine if you are aiming at a rather reliable range of iodine intake.

Or even better, iodine supplements

If you consume a very low-salt diet, get a good iodine supplement, preferably pharmaceutical-grade.

  • Best of the best: Pharmaceutical-grade prescription iodine

    Did you know the iodine in your iodized last is extracted from seaweeds? So the same concerns you would have for seaweeds (heavy metals, sea-borne contaminants etc…) are legitmate to have when it comes to iodized supplements. Supplements also being very poorly regulated worldwide, my current advice is to always try to get the pharmaceutical grade,  prescription-only iodine. The dosage will be very precise, contaminants likely checked for, and manufacturing process perhaps not perfect but far more regulated and accountable than free-market supplements.
    Dealing with probable relunctance from your G.P.: If your diet has such incredibly low salt that you are realistically at risk of a predictable iodine deficiency, there is no reason why a G.P. would not take you seriously when you request an iodine prescription. You may just need to be ready that they would suggest seafoods and free-market supplement and you may need to be ready to tell them kindly why that is not an option for you. I would change GPs (and I have been) if he/she does not generally share similar views on nutrition and prevention.
    I strongly believe in prevention over therapy, it also costs less in many ways. But unfortunately the practice of things, still reserves a lot of supplements and testing to pathologies rather than preventive actions. You may experience that worldview from your doctor when you ask him/her for supplements or preventive/routine testing in a non-therapeutical context.

  • If you still want “free-market” supplements

    If this is not available to you, or you still prefer free-market supplements, get a clean iodine supplement (i.e. low on heavy metals). I looked at this link, the only (apparently) genuinely independent lab that looked at the heavy metals. Strangely it did not look at iodine content itself! At the moment I write this, I roughly trust this source but have not examined it thoroughly enough. If you have researched the trustworthiness of the Health Ranger, (whom as supplement vendor might or not have a conflict of interest) please comment below.

Exploring further

Comprehensive Handbook of Iodine: Nutritional, Biochemical, Pathological and Therapeutic Aspects

Selenium variation in Brazil nuts – Can we get all our selenium from Brazil nuts?
Sources:
[1] Research on Iodine Deficiency and Goiter in the 19th and Early 20th Centuries
[2] IODIZED SALT by The Salt Institute – July 13, 2013
[3] Iodine, New Zealand Ministry of Health
[4] Are vegetarians an ‘at risk group’ for iodine deficiency? British Journal of Nutrition (1999), 81, 3–4
[5] Based on the works of Claude & Lydia Bourguignon.
[6] Analysis of iodine content in seaweed by GC-ECD and estimation of iodine intake
[7] SURVEY OF IODINE LEVELS IN SEAWEED AND SEAWEED CONTAINING PRODUCTS IN AUSTRALIA
[8] Notification details – 2005.050 RASFF Portal
[9] Iodine speciation studies in commercially available seaweed by coupling different chromatographic techniques with UV and ICP-MS detection