Arsenic in Kelp Supplements

Just updated the Iodine page of regarding arsenic in kelp supplements:

“Most iodine supplements are simply tablets made from kelp. Being a seaweed, kelp likely contains at least small amounts of arsenic. There are some very rare cases in which people taking kelp supplements have developed symptoms of arsenic toxicity (8). A survey of kelp supplements in the U.S. found that eight out of nine batches contained some level of arsenic (8). Another survey in the UK of imported seaweed found very little arsenic in kelp, and no detectible amounts of inorganic arsenic, which is the harmful type (9).

“It is very unlikely that, taken at recommended amounts of 150 µg every other day, arsenic toxicity is likely to occur from kelp supplements. However, if you are concerned, at least one company makes iodine tablets that appear not to come from kelp: Nature’s Plus Potassium Iodide.”

Some additional notes:

The highest level of arsenic found in U.S. supplements was 65.5 mg/kg (8). My iodine supplement contains 225 µg of iodine in 45 mg of kelp. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has set a tolerable intake of 15 µg/kg of body weight per week (9). For a 140 pound person, that would be 953 µg per week. Supplementing three times per week with these tablets, at the highest toxicity level found, arsenic exposure would be 8.8 µg per week, well below the 925 µg level.

Wakame, kombu, and arame are all types of kelp.


8. Amster E, Tiwary A, Schenker MB. Case report: potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007 Apr;115(4):606-8. Epub 2007 Jan 18.   |   Link | Follow-up letters to the editor.

9. Rose M, Lewis J, Langford N, Baxter M, Origgi S, Barber M, MacBain H, Thomas K. Arsenic in seaweed–forms, concentration and dietary exposure. Food Chem Toxicol. 2007 Jul;45(7):1263-7.   |   Link

35 Responses to “Arsenic in Kelp Supplements”

  1. AmyLu Says:

    Do you know if the organic certification process for sea vegetables as foods rules out arsenic, or is it caveat emptor?

  2. Jack Norris RD Says:


    I’ve never heard that it does.

  3. AmyLu Says:

    Okay, thanks! How often do you find it safe to eat sea vegetables, given that that is the case?

  4. Jack Norris RD Says:


    The second study linked to above examined arsenic in kelp (arame, wakame, and kombu), hijiki, and nori. The researchers concluded that only hijiki had enough arsenic to be worried about. I personally would not eat more than 3 servings of seaweed a week unless I knew where it was coming from, but that’s just an arbitrary guess.

  5. Joe Mosely Says:

    Toxity of organic and inorganic arsenic is very different. The cases reported above did not differentiate and may be causing undo alarm. The symptoms exhibited by the patient were not classic arsenic toxicity symptoms. When discussing these cases the following analysis should also be cited. One can also research organic and inorganic arsenic to become more educated.

  6. Jack Norris RD Says:


    Do you work with the supplement industry? I included a link to that letter in the citation for reference 8 in my post.

  7. Dan Hackam Says:

    Very interesting. I have started taking an iodine supplement based on the recommendations on your site. It contains 50 to 150 micrograms per kelp tablet. However, I also note that I eat alot of yogurt (twice per day), and wonder if that would contain an adequate dietary supply due to the use of iodine in the dairy process (cleaning of teats and so forth). I don’t eat any seaweed – I tried cooking this one day, and found the smell and taste to be foul.

    Other supplements I ingest – vitamin D 1000 IU od, vitamin B12 100 mcg OD, omega-3 containing 600 mg of EPA+300 mg of DHA. I am a “lacto-vegan”, but my only source of dairy is yogurt. I eat soy twice daily.

  8. Jack Norris RD Says:


    I have not done an analysis on how much iodine is in yogurt, though you could check it out at (those numbers should only be considered to apply to the US, though – and I don’t even know if they list iodine). The amount you’re taking sounds like a safe amount to me, even if there is iodine in your yogurt.

  9. Dan Hackam Says:

    Thank you for the info. I greatly enjoyed all the information on your site and read the original articles in JCEM on iodine deficiency in vegans.

  10. Alessio Says:

    I’m vegan, and I regularly take a kelp supplement.
    In particular, I use this one:

    I’d like to know what do you think about the risk of radioactive elements contamination of seaweed.
    For example, colud kelp supplements be contaminated with radioactive iodine?
    Thank you so much for your possible reply!

  11. Jack Norris RD Says:


    I don’t know anything about it. You might contact Solgar and ask if they are taking any steps to protect their kelp from radiation. If you do and they answer, please let us know.

  12. Heather Guidi Says:

    I too am concerned about the purity of the kelp in the supplement I am taking.
    I have just written “The Vitamin Shoppe” asking for info. I will share if they respond.
    I am also wondering about ” nascent iodine” maybe this is a better way to get Iodine.

  13. Jack Norris RD Says:


    I had never heard of nascent iodine before your comment and can’t find any information on it from reputable sources (not even Wikipedia!). I’m not a biochemist, but it sounds like hocus pocus to me and I personally wouldn’t mess with it (unless I found out more from a reputable source – not Mercola).

  14. AmyLu Says:

    Hi, Jack,
    I saw some referenced info online about nascent iodine. I have no affiliation with this site and don’t know if this (or the references it cites) would be helpful to Heather’s question, but here it is:

  15. Jack Norris RD Says:


    That links isn’t working for me.

  16. AmyLu Says:

    Try this, I copied and pasted it instead of retyping it this time:

    If that doesn’t work, I got to it from a Google search on the term “nascent iodine”

  17. Jack Norris RD Says:

    Okay, yes I saw that page when I was searching. It didn’t seem very reliable to me.

  18. David Says:

    I took a Natures way kelp supplement for 2 days, 1 pill per day, 440 mcg iodine. I stopped after having a reaction- nausea, runny nose, loss of appetite, sleeping during the day, insomnia at night. I have never been tested for an iodine deficiency, but I read most Americans are deficient. I have no known thyroid issues.
    Is my reaction the body trying to detoxify itself, should you even supplement with iodine from kelp and is 440 mcg iodine the right amount from a supplement?

  19. Jack Norris RD Says:


    The RDA is 150 micrograms. 880 over two days is a lot, but I am surprised to hear of your reaction. I wonder if you are allergic to something in the preparation. In any case, you need a different source of iodine. Do you salt your food? If so, using iodized salt can probably cover your needs. There’s also seaweed if you eat it a couple times a week.

    > but I read most Americans are deficient.

    To my knowledge, that is not true. Even most vegans in the US are getting enough iodine (though intakes for vegans would ideally be higher than they are). Check out this page:

  20. Alessio Says:

    I wrote to Solgar, and I’ve just received their reply.
    Unfortunately their kelp isn’t tested for contamination with radioactive elements.
    So I suspect there are no kelp supplements, on the market, tested for radioactive contamination. 🙁

  21. Jack Norris RD Says:


    Thanks for the follow-up. That’s unfortunate.

  22. David Says:

    Thanks for the update. I usually use sea salt, I’m not sure if it is iodized.
    I made a bad assumption, taking 1 kelp pill would be an appropriate amount, but as you stated, 440mcg is 3x the RDA recommendation.
    I can look for the article I was reading, the doctor claims that a cause of a weakened immune system is low iodine level. I think he did recommend taking in more than than the RDA daily allowance.

  23. Jack Norris RD Says:


    Sea salt is not iodized.

  24. David Says:

    Here is a link to the website of Dr. Flechas-

    He does recommend testing your iodine levels first, and cautions against taking seaweed supplements.

    He makes the connection between low iodine levels and forms of cancer, and links high iodine level to lower cancer rates in Japan, as “the average Japanese eats around 13.8 mg of iodine per day with the vast majority of that iodine coming from seaweed that has been specifically grown and cultured to maximize iodine trapping in the seaweed.”

  25. Jack Norris RD Says:


    My understanding is that urinary iodine testing only shows someone’s iodine intake for a brief moment (24 hours?) in time. I don’t have time to carefully read all of Dr. Flechas’ info, and I cannot tell if the papers he cites were published in scientific journals or only on his website. I tend to trust the Linus Pauling Institute:

    They suggest potassium iodide at 150 micrograms per day – you might look into getting a potassium iodine supplement.

    It could be that you’re just allergic to kelp, by the way.

  26. David Says:

    Thanks Jack, it is entirely possible I am allergic to kelp. I took 1 pill Thursday and 1 pill Friday, and then stopped when I noticed side effects. Even though it has been a week, I still feel some of the side effects, like not sleeping through the night.

  27. Shyah Says:

    Does Nature way kelp contain pork from the gelatin ingredient?

  28. HarryLlama Says:

    Jack, I’m wondering about other heavy metals in seaweed in addition to arsenic, like cadmium and mercury. Do you know whether any of the commercial retailers test their products? Any research on this that you’re aware of? I try to eat organically grown produce, but that’s not possible with seaweed products, I imagine. I’d like to get my iodine from seaweed rather than table salt, but not if I’m also getting toxins. Thanks!

  29. Jack Norris RD Says:


    I’m afraid I haven’t seen data on the heavy metals in seaweed.

  30. Mark Says:

    I bought Thyroid Complex Supplement two weeks ago from Vitamin Shoppe. Among the ingredients are the following:


    L-Tyrosine • 150 Mg

    I have been taking 3 tablets per day as directed. However, I started with diarrhea as well as some headacke. Last night I started to experience stomach nausea. I know that these can be allergic reactions to either Kelp or L-Tyrosine. However, I read THE BENEFITS OF KELP, by Dr. Lawrence Wilson at in which he mentioned that many kelp supplements contain arsenic.

    He stated as follows:

    “The brand of kelp matters. The reason is that some brands are using other plants that are actually not kelp. These brands contain bladderwrack or other sea vegetables that are somewhat toxic.
    Confusion about the word ‘kelp’. Occasionally, a bottle of so-called kelp is not really kelp, but bladderwrack or another seaweed. In these cases, we have found toxic metal problems.
    Safe brands of kelp, so far, are the ones listed below:

    Nature’s Way, Endomet, Solaray, Country Life, Now, Ecological Formulas, Office Gudni Gudnason, Azure Farm, Solgar, Frontier Herbs, Monterrey Bay Herb Company and kelp from

    I do not recommend other brands of kelp. They are different plants and are somewhat toxic. A brand that I definitely do not recommend at this time is Maine Sea Coast Kelp. It is somewhat toxic.”

    Have you heard from Heather Guidi who in her November 19th, 2013, e-mail stated that she was awaiting a response from the Vitamin Shoppe on whether their kelp supplement contains any impurities?

    I plan to send an email to Vitamin Shoppe and to Dr. Wilson as well to find out whether the kelp supplement contains any impurities.

    I live in Guatemala. The Vitamins here are of very poor quality. This Vitamin Shoppe product is one the few that I have found for Thyroid Support. I think there is one location far from me that sells a NOW Thyroid Support product containing kelp. I may have to buy that instead.



  31. Jack Norris RD Says:


    I don’t think I’ve heard from Heather since there’s nothing on this page.

    I can’t tell if each tablet contains 150 µg or if 3 tablets contain a total of 150 µg. I’d stick closer to an intake 150 µg per day than to 300 or 450 µg.

  32. Mark Says:



    I found out that the problem was a liduid iron supplement that I had started taking last Saturday. I have stopped taking it. The one teaspoon dose contains 27 mg of iron which is too much for me.

    Dr. Wilson communicated with me but he mentioned Thyro-complex from Endomet Labs that contains Kelp is very good. He did not tell me about the Kelp in Thyroid Complex from Vitamin Shoppe.


  33. Martin Meyer Says:

    First of all I’m an Icelandic nutritionist.

    Your thinking is right dear writer, however there is a BIG flaw!

    (JECFA) has set a tolerable intake of 15 µg/kg NOT mg/kg!
    Check out your link again if you don’t believe me.

    For a 140 pound woman (63,5 kg) the weekly tolerable intake is 952 µg/week or 0,952 mg per week.

    Per day it is 952µg/week / 7 = 136µg/day or 0,135 mg/day.

    Supplementing three times per week at the highest txicity level found, arsenic exposure would equal to 1,56600 micrograms*3 = 0.004698 mg.

    – “The highest level of arsenic found in U.S. supplements was 34,8 mg/kg”
    – “My iodine supplement contains 225 µg of iodine in 45 mg of kelp (o,o45 g kelp)”

    0,000045kg of kelp * 34,8mg/kg = 0.001566mg of arsenic per serving.
    0,001566mg to µg is 1,56600 micrograms.

    In my experience: I’m 83kg * 15 µg/kg = 174.3 µg per day.
    I take 0.07g of kelp daily = 350 µg iodine.

    34,8 mg/kg*7,0 × 10-5 * = 0,002436 mg/serving.
    Supplementing everyday at the highest txicity level found, arsenic exposure would equal to 2,43600µg per day

  34. Jack Norris RD Says:


    Thank you for pointing out the error in the units for the Expert Committee on Food Additives’s weekly tolerable intake. Although I had the units wrong, the math and conclusions were otherwise correct. However, after you brought this to my attention, I carefully went through the article I’d referenced and discovered that I made a different error that was materially more important—the highest level of arsenic found in the Ross et al. 2007 study was not 34.8 mg/kg, but rather 65.5 mg/kg. This changed the weekly potential for arsenic intake from 4.7 µg to 8.8 µg, which is almost twice as much, though still much lower than the 952.5 µg per week limit for a 140 lb person.

    In 2017, a report found arsenic contamination in one of six supplements they tested in the U.S. That’s a much better ratio than Ross et al. found in 2007, so hopefully there’s less contamination in general. At the same time, ConsumerLabs found too much iodine and between this and the potential for arsenic contamination, I’d suggest people opt for a potassium-iodine supplement that isn’t from kelp.

  35. MARK J SPARTZ Says:

    Great thread Jack. I’ve been taking kelp for 8 weeks and have has terrible symptoms…red rash on front of neck, insomnia, muscle weakness, racing heart and hot flashes at night…needless to say I stopped taking it and within 3 days most of the symptoms have diminished. I think I’ve overdosed on iodine, and I understand it takes weeks to completely flush from the body. Never taking kelp again!

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