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Seaweed Iodine Varies From 16 to 2,984 Micrograms a Gram
The NIH reports that seaweeds hold between 16 and 2,984 micrograms of iodine per gram, a spread of about 190 times. Nori flakes give 116 micrograms in 5 grams. A formula with four seaweeds can therefore vary a lot between batches unless the maker tests and standardises each lot.
Written by the Prostadine label deskUpdated · 4 min read
The basics01
How wide is the range?
Very. The NIH Office of Dietary Supplements reports that seaweeds range from 16 to 2,984 micrograms of iodine per gram (NIH ODS, Iodine).
That is roughly a 190-fold difference. A gram at the low end gives about a tenth of a day's need. A gram at the high end gives about twenty days' worth, and nearly three times the adult upper limit.
The range exists because iodine in seaweed depends on the species, the sea it grew in, the season, the part of the plant and how it was dried or processed.
The evidence02
What is the figure for common seaweeds?
| Item | Iodine |
|---|---|
| Dried nori, 2 tablespoons (5 g) | 116 micrograms (NIH ODS, Iodine) |
| Lowest seaweed in the NIH range | 16 micrograms per gram |
| Highest seaweed in the NIH range | 2,984 micrograms per gram |
| Adult daily need | 150 micrograms |
| Adult upper limit | 1,100 micrograms |
The nori figure shows that a common seaweed snack carries most of a day's need in a spoonful. Kelp species sit at the other end, and brown seaweeds in general tend to be the richest.
The numbers03
Why does batch-to-batch variation matter?
Two harvests of the same species can differ a lot, and a maker blending four seaweeds adds the variation together. Without testing each lot for iodine, the amount in a bottle can drift up or down, and so can the dose you take.
A careful maker tests the raw material, sets a target per serving and checks the finished lot. That produces a number for the label. When no number is printed, a reader cannot tell whether the maker did this work, and the bottle's iodine remains a guess.
The catch04
Who is most affected?
A healthy adult with a normal thyroid copes with a wide range. The groups most at risk from excess are older adults, pregnant and breastfeeding women, infants and people who already have thyroid disease, according to the American Thyroid Association (ATA, Excess iodine).
The ATA also says that some kelp and iodine supplements hold up to thousands of times the upper limit, and advises against supplements giving more than 500 micrograms a day. Those are not statements about Prostadine. They are the reason a lab figure is worth asking for.
Safety05
Do seaweeds carry anything else?
Sea plants take up what is in the water, and that can include arsenic, cadmium and mercury when the water is polluted. MSK notes this for bladderwrack harvested from contaminated waters (MSK, Bladder wrack).
A certificate of analysis that lists metals as well as iodine would answer both questions at once.
A lab report for your lot should show iodine in micrograms per serving and test results for heavy metals.
What to do06
What can you do in the meantime?
Count the seaweed you eat. If you often eat sushi, seaweed salad or soup with kelp, note it, and consider eating less while you test the drops. Our iodine page has a calculator to show your headroom under the upper limit.
Tell your doctor about the drops and your seaweed habits before a thyroid test, so the result is read correctly.
FAQ07
Prostadine questions people ask
Why does seaweed iodine vary so much?
It depends on species, sea, season, plant part and processing. The NIH reports a range of 16 to 2,984 micrograms per gram, which is about 190-fold.
How much iodine is in a sheet of nori?
The NIH gives 116 micrograms for 2 tablespoons (5 g) of dried nori flakes. A sheet differs by weight, so the figure is a guide, not a rule.
Is kelp higher in iodine than nori?
Brown seaweeds such as kelp tend to be richer, and the top of the NIH range belongs to them. Exact values vary by species and batch.
Can I find out the iodine in my Prostadine bottle?
Only from the seller. Ask for a lab report for your lot that gives iodine in micrograms per 2 mL serving, plus metals. The label does not print it.
Who wrote this08
Written and reviewed by
Pages built from the bottle photos, the info page and linked NIH, FDA, NCI, FTC and peer-reviewed sources.
Last updated . Read our editorial standards and how we check reviews. This website is run by a licensed U.S. retail desk for Prostadine, not by the manufacturer. We earn money when you buy through our order links.
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