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