Which Seaweed is Most Protective Against Breast Cancer?

Which Seaweed is Most Protective Against Breast Cancer?
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Nori seaweed snacks may favorably alter estrogen metabolism by modulating women’s gut flora, resulting in decreased breast cancer risk.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Unfortunately, as the traditional diets of East Asia Westernize, their breast cancer rates have risen, which some have linked to a quadrupling of animal product consumption.

This is the breast cancer rate of Japanese women living in Japan. If they emigrate to the United States, within ten years, they’re up to here. And, if they hang around long enough, here’s the risk of resident Japanese-Americans living in the United States. Note, though, that’s still somewhat lower than the U.S. national average. This may be because of some of the dietary habits may carry with them—soy consumption, green tea, maybe eating more mushrooms. But maybe, partly, it’s the seaweed.

We’ve known for over a decade that in vitro, in a petri dish, seaweed broth is effective at clearing cancer cells. Here’s three different types of human breast cancer, measuring cancer cell death. Here’s what a widely used chemotherapy drug can do, and here’s seaweed. Worked even better, and, unlike the chemo, didn’t hurt normal, noncancerous breast cells. But, what about outside of the test tube, in people?

Well, a population study comparing women with breast cancer, to women without, found that consuming a single sheet of nori a day may cut a woman’s odds of breast cancer in half. We think it’s because seaweed favorably alters estrogen metabolism—likely due to a modulation of the woman’s gut bacteria. It appears the more seaweed you eat, the less estrogen you have in your system, which may lower breast cancer risk.

This may be because of all the fiber in sea vegetables. Or, it may block the enzyme that undermines our body’s attempt to flush out excess hormones—or, even somehow interfere with estrogen binding to estrogen receptors. Either way, to effectively lower one’s estrogen levels, Asian women may be able to get away with maybe one sheet of nori a day. But, American women are so much bigger that it may take closer to two. There’s lots of yummy seaweed snacks out there to make it a tasty experience—just try to get some low-fat, low-sodium ones.

Wakame, the seaweed used fresh in seaweed salads, unfortunately did not appear to reduce breast cancer risk, though it has been found to rather dramatically lower blood pressure in hypertensives. Just two teaspoons of seaweed salad a day for a month dropped their blood pressure 14 points. And, after two months, was associated with up to a two-inch skinnier waistline.

As I’ve mentioned before, though, I’d recommend avoiding hijiki, which tends to have too much arsenic, and kelp, which tends to have too much iodine. In fact, too much seaweed of any type may actually increase one’s risk of thyroid cancer, because of the amount of iodine you’d be taking in.

But, there does not appear to be increased risk at the levels of consumption I’m talking about—like, you know, a sheet of nori every day. And, a study of seaweed eaters in California actually found decreased risk. But, again, we’re talking, you know, kind of modest levels of intake.

You know, I’ve frequently talked about the benefits of dietary diversity—eating different families of fruits and vegetables, eating different parts of individual plants; like beets, and beet greens. If we just stick to land plants, though, we’re missing out on all the plants from the other 70% of planet Earth. Sea vegetables have phytonutrients found nowhere else, types of fiber, and unique carotenoids, and polysaccharides, and various polyphenol defense compounds, each of which may have anticancer properties. So, I encourage everyone to try experimenting with sea vegetables until you find one you like, even if that means just sprinkling some powdered dulse on your food.

Please consider volunteering to help out on the site.

Images thanks to Emily Barney and jessica wilson {jek in the box} via flickr; and Agricultural Research Service, Alice Wiegand, and Lyzzy via Wikimedia. Thanks to Ellen Reid and Shane Barrett for their Keynote help.

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Unfortunately, as the traditional diets of East Asia Westernize, their breast cancer rates have risen, which some have linked to a quadrupling of animal product consumption.

This is the breast cancer rate of Japanese women living in Japan. If they emigrate to the United States, within ten years, they’re up to here. And, if they hang around long enough, here’s the risk of resident Japanese-Americans living in the United States. Note, though, that’s still somewhat lower than the U.S. national average. This may be because of some of the dietary habits may carry with them—soy consumption, green tea, maybe eating more mushrooms. But maybe, partly, it’s the seaweed.

We’ve known for over a decade that in vitro, in a petri dish, seaweed broth is effective at clearing cancer cells. Here’s three different types of human breast cancer, measuring cancer cell death. Here’s what a widely used chemotherapy drug can do, and here’s seaweed. Worked even better, and, unlike the chemo, didn’t hurt normal, noncancerous breast cells. But, what about outside of the test tube, in people?

Well, a population study comparing women with breast cancer, to women without, found that consuming a single sheet of nori a day may cut a woman’s odds of breast cancer in half. We think it’s because seaweed favorably alters estrogen metabolism—likely due to a modulation of the woman’s gut bacteria. It appears the more seaweed you eat, the less estrogen you have in your system, which may lower breast cancer risk.

This may be because of all the fiber in sea vegetables. Or, it may block the enzyme that undermines our body’s attempt to flush out excess hormones—or, even somehow interfere with estrogen binding to estrogen receptors. Either way, to effectively lower one’s estrogen levels, Asian women may be able to get away with maybe one sheet of nori a day. But, American women are so much bigger that it may take closer to two. There’s lots of yummy seaweed snacks out there to make it a tasty experience—just try to get some low-fat, low-sodium ones.

Wakame, the seaweed used fresh in seaweed salads, unfortunately did not appear to reduce breast cancer risk, though it has been found to rather dramatically lower blood pressure in hypertensives. Just two teaspoons of seaweed salad a day for a month dropped their blood pressure 14 points. And, after two months, was associated with up to a two-inch skinnier waistline.

As I’ve mentioned before, though, I’d recommend avoiding hijiki, which tends to have too much arsenic, and kelp, which tends to have too much iodine. In fact, too much seaweed of any type may actually increase one’s risk of thyroid cancer, because of the amount of iodine you’d be taking in.

But, there does not appear to be increased risk at the levels of consumption I’m talking about—like, you know, a sheet of nori every day. And, a study of seaweed eaters in California actually found decreased risk. But, again, we’re talking, you know, kind of modest levels of intake.

You know, I’ve frequently talked about the benefits of dietary diversity—eating different families of fruits and vegetables, eating different parts of individual plants; like beets, and beet greens. If we just stick to land plants, though, we’re missing out on all the plants from the other 70% of planet Earth. Sea vegetables have phytonutrients found nowhere else, types of fiber, and unique carotenoids, and polysaccharides, and various polyphenol defense compounds, each of which may have anticancer properties. So, I encourage everyone to try experimenting with sea vegetables until you find one you like, even if that means just sprinkling some powdered dulse on your food.

Please consider volunteering to help out on the site.

Images thanks to Emily Barney and jessica wilson {jek in the box} via flickr; and Agricultural Research Service, Alice Wiegand, and Lyzzy via Wikimedia. Thanks to Ellen Reid and Shane Barrett for their Keynote help.

Doctor's Note

Seaweed snacks are like kale chips—munchies made out of dark green leafy vegetables. Can’t beat that!

More on some of the other protective dietary components in the diets of Japanese women in Why Do Asian Women Have Less Breast Cancer? and Breast Cancer Survival & Soy.

If you dig anticancer comparison videos, make sure you also check out Which Fruit Fights Cancer Better? and #1 Anticancer Vegetable.

I’ve done videos on why hijiki (Avoiding Iodine Deficiency) and kelp (Too Much Iodine Can Be as Bad as Too Little) are not the best choices.

If you’d rather stick to terrestrial plants, see Preventing Breast Cancer by Any Greens Necessary. And, for more on lowering breast cancer through diet:

And more on the importance of dietary diversity in Garden Variety Anti-Inflammation, Apples & Oranges: Dietary Diversity, and Constructing a Cognitive Portfolio.

For more context, check out my associated blog: Which Seaweed to Help Prevent Breast Cancer?

If you haven’t yet, you can subscribe to my videos for free by clicking here.

47 responses to “Which Seaweed is Most Protective Against Breast Cancer?

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  1. Our favorite sea vegetables are dulse and nori. The nori we have left in our stash we purchased pre-Fukishima calamity. I’ve never seen nori for sale that didn’t come from Japan (or at least the Pacific) – do you think its health-promoting properties override any radiation (and other toxins and pollutants) it might contain? Too bad life’s not more simple, our species sure knows how to garp things up.




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    1. re: “Too bad life’s not more simple, our species sure knows how to garp things up.”

      Argh. I agree! To eat seaweed-to not eat seaweed. It’s not an easy decision to make now-a-days. Personally, I still eat it. I live on the American west coast and figure I’m probably getting plenty of Fukishima radiation directly from the air and other foods grown locally here. So, I might as well get the benefit of the seaweed.

      But note that’s not an educated opinion as I don’t have the information to balance the risks. That’s just my thinking right now and I thought the perspective might be helpful.

      If you haven’t seen it yet, Dr. Greger has a video on this topic:

      http://nutritionfacts.org/video/fukushima-and-radioactivity-in-seafood/

      Good luck.




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    2. I think there is a lot of seaweed that is packaged in Japan but sourced from China. At least that’s what I found last time I went to our local Japanese grocery store. I worry about contamination.




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  2. This is great news. My seven year-old son LOVES toasted Nori. I limit him to 2 sheets/day but he would gladly eat more. It is his absolute favorite food! I also enjoy it. I am also glad to hear about the safety of Wakame, which I use to make broths. I had wondered about it since hijiki and kelp are best to be avoided. Thanks!




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  3. I absolutely love those roasted, oiled and salted nori packets that can be attained from Trader Joes (it was even pictured in the video). But as Dr. Greger cautioned, it would be best to stay away from the added oil and salt. I tried purchasing the sheets of plain, roasted nori, but I just don’t like them. I eat a packet-a-day of the Trader Joe’s stuff, but am I doing myself more harm than good with the included oil and salt too? I don’t know the impact of the whole food. (Of course, I do know the impact on the environment is inexcusable.)

    My other issue with the nori is the iodine levels. One of the reasons I want to eat the snack nori (aside from the pleasure) is for the iodine, which I especially need to balance out the healthy veggies that I eat. I know Dr. Greger has a video on this topic, but if memory serves, I haven’t been able to find any good data that assures me that the product I’m actually eating has consistent and adequate iodine. (I don’t get the iodine in my salt because I happen to like the super-fine sea salt that I get. So, I’ve been blindly banking on the nori snacks.)

    All of that aside, it is awesome to learn from this video that there may be even more health benefits than I had originally thought from eating my daily packet (or sometimes 2) of nori.




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    1. Hi Thea,
      I put my nori sheets on my toaster (it has a top for rolls that pops out) and put the toaster on max for 2 times per side. I then cut up the nori sheets into strips. They taste a lot better when toasted and become crunchy. I don’t have Trader Joes here on this side of the planet, so I can’t compare…




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    2. I don’t care for the plain nori sheets either, but what about putting a nori sheet in a fruit/green smoothie? You wouldn’t even know that it’s there. The great thing about nori, it is the least contaminated sea vegetable.




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        1. Yeah, I can’t notice that the sheet of nori is even in the smoothie. I make a sweet smoothie, though, with water, dates, berries, whole power greens salad from trader joes, purple cabbage, beet root, nori sheet, flax.




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  4. I wish I could open a package of hot teriyaki nori without eating all 80 chips. Its a regular shopping list item when I visit the local Asian grocery.

    To date, there don’t appear to be any published studies of post-Fukushima radiation in edible seaweed. In this late 2012 video on the resumption of Miyagi province nori production, no contamination was found, but this early 2012 video from South Korea strikes a cautionary note.

    It plausible that regular currents drew radioactive seawater south from Fukushima and out to sea (sparing famed Miyagi yakinori).




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  5. I know that the safe upper limit of iodine is around 1100 micrograms, shades of excitement! And all sea vegetables are packed packed packed with iodine. So what’s the safe upper limit of sea veggies??????? Do tell!! maybe 2 to 4 ounces once or twice a week. Do tell Do tell !!!




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  6. Hi Dr Greger,
    Once again, a heart-felt “thank you” for your amazing site and the information you have provided. Implementing your dietary advice is having a profound impact on my health and weight.
    I have one question with regards to the incorporation of sea vegetables in my diet. Given, that a lot of the sea vegetables are harvested in the oceans around Japan, I am concerned regarding radio-activity and heavy-metal content of sea vegetables from the leakage of contaminated groundwater from the Fukishima Nuclear Reactor. Could you please advise?
    kind regards,

    Ben




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  7. Love these gems from the peer reviewed literature. Thanks! I have acquired a taste for nori seaweed. I get it at Costco and it comes from Korea – away from the prevailing currents from eastern Japan.

    Thankfully, my breasts are not as susceptible to breast cancer as those of women. On the other hand, women don’t have to contend with an aging prostate. I have noticed that Dr. Greger has reported on several foods that help prevent breast cancer but also seem to help prevent prostate cancer. Dr. Greger, have you noticed any studies on seaweed and prostate cancer?




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  8. I guess my next prescription could be Rp plants, No as much as possible, Ds 3-4 times a day, prophylactic against cancer, CVD, inflammation, diabetes and hypertension (side effects: None)




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  9. If you already have cancer, however (or perhaps “have had,” a tense of the verb we survivors yearn to use) , stimulating thyroid function could be risky. Dr. Aleck Hercbergs of The Cleveland Clinic has addressed this in several papers. How much iodine is in nori–and how does that compare to other sea vegetables? –Harriet at http://www.eatandbeatcancer.com




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  10. The “experts” in the scientific community now say that seaweeds are not plants, animals, or fungi but should be placed in several separate kingdoms outside of the plant kingdom.

    As for the wonderful benefits of eating seaweed, let’s not forget that sea salt always contains cancer-causing nitrosamines and nitrites. Fortunately, the salt can be easily and quickly washed away before eating the seaweed but unfortunately, most people can’t resist the temptation to eat seaweed deliciously.




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    1. Sea salt is basically comparable to table salt and what nutrients are in sea salt are so small they are basically negligible.

      1 tsp of Sea Salt contains

      12 mgs of calcium

      7 mgs of potassium

      27 mgs of magnesium

      The recommended daily values of these nutrients are

      600 mgs of calcium

      4700 mgs of potassium

      400 mgs of magnesium

      So to get just 25% of this daily value, we would need to eat

      Calcium, we would need to take in 24,600 mgs of sodium

      Potassium, we would need to take in 335,000 mgs of sodium

      Magnesium, we would need to take in 7,407 mgs of sodium




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    2. Biologists can’t agree on the total number of kingdoms that all living
      things should be divided into. Many of the most modern biologists prefer
      to create eight separate kingdoms instead of the just four, five, or
      six kingdoms preferred by past biologists.

      Seaweeds belong to three kingdoms:
      Kingdom Plantae (chlorophyte, or “green” algae seaweeds),
      Kingdom Plantae (rhodophyte, or “red” algae seaweeds),
      Kingdom Chromista (phaeophyte, or “brown” algae seaweeds)
      Kingdom Chromista (xanthophyte, or “yellow-green” algae seaweeds), and
      Kingdom Bacteria (cyanophyte, or “blue-green” algae seaweeds).

      Seaweeds that belong to the Kingdom Plantae are plants; the others,
      strictly speaking, are not. Kombu (kelp), arame (kelp), limu moui
      (kelp), hijiki, mozuku, and wakame are not plants. Wikipedia places them
      under Kingdom Chromalveolata because they are classified as “brown”
      algae seaweeds. However, nori (laver), ogo (limu), and dulse are
      classified as “red” algae seaweeds and are placed under Kingdom Plantae.

      Kingdom Protista, which includes the chlorophyll-containing,
      self-propelling euglenozoa, is a fourth kingdom of algae which contains
      no species of seaweeds.




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  11. I wonder why Nori works while Wakame doesn’t. Thanks to the Doc, I developed a taste for Dulse. Thought I try not to eat too much in order not to have too much Iodine.




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  12. Hi Dr Greger,
    I’ve been taking in your nutritional advice one video at a time, and it’s been ever so rewarding. In fact, I took up running, because I felt a need to spend excess energy, this is an absolute first for me!
    Anyways, here’s my question I’ve been buying from asian markets, and so many dried products (like nori) include a little sachet that reads “absorptive chemicals to protect the content against humidity.” Any idea of its safety level?
    Thanks a bunch.




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  13. Eating a sheet of nori each day is so easy to do…and now I’m finding out that one of my cats also loves it!!! I tear off a few small pieces for her and she gobbles it up!
    v




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    1. val: My dog loves the stuff too. :-) On the other hand, my dog is a bit ‘out there’ in terms of his tastes. He’s a big fan of many fruits and veggies, including broccoli and kale stems and sugar snap peas, etc.




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      1. Thea, our dog, a black lab, eats bananas, (to include the skin when we’re not watching!), blue sweet potato skins, apple skins, watermelon rind, winter squash which he has “stolen” from me, and thick broccoli stalks–not to mention the core of cauliflowers. I think he will live longer than average. :D




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        1. Johanna: I think your dog will live longer than average too! My dog is a Great Dane. He’s 12, where the vast majority of Great Danes live 8-10. My dog has been on a vegan kibble since he was 6. Go veggie dogs!




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  14. Hi Dr, I love your videos and am very glad you do the work you do. I am wondering about the levels of heavy metals in sea vegetables and health risks involved considering polluted waters?




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  15. I eat around six to eight full raw seaweed sheets per day with my rice and kimchi, and well, practically anything else I consume… Is this too much seaweed? My family think I’m nuts, but I just love the taste of nori and it pairs well with nearly anything! I also consume quite a bit of tofu each week, sometimes averaging about 4 containers (large blocks) worth, simply because I adore the taste! Everyone tells me that this much soy and seaweed is harmful, etc., etc. I’d really like an actual expert’s opinion, please!!!! :)




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    1. Sarah Tabler: I’m not an expert. But I noticed that no one responded to you, so I thought I might be able to be helpful.

      re: Soy.
      That one is easy. Dr. Greger did a series on soy. One of the videos in the series concluded that 3 to 5 servings a day of soy can be healthful. In his book, How Not To Die, Dr. Greger defines a serving of tofu as 1/2 cup. Knowing serving size is key to helping you figure out if 4 containers (say 4 pounds) of tofu a week is healthy or not. I’m *guessing* that it is just fine. With 1/2 cup servings and 5 servings in a day, that would be 2.5 cups tofu. And isn’t that about what you get from a block? (This is the part I’m not sure of as I don’t have a block in front of me right now.) And you aren’t eating a block every day. Just about every other day. So, that really should be fine.

      On the other hand, note that in How Not To Die, Dr. Greger recommends a target of 3 servings of beans a day as part of the Daily Dozen. And tofu counts as a bean. So, you may want to adjust your calculations for 3 servings of tofu instead of five and see how it all pans out. But even if you are exceeding the 3 servings of tofu a day, I don’t know if that is a bad thing as long as you are under the 5 servings a day. I say that, because Dr. Greger has referred to the Daily Dozen as ‘targets’. I interpret that to mean that as long as we are meeting targets and not exceeding our calorie needs, we can eat more of those categories as desired.

      Here is the video I mentioned above. http://nutritionfacts.org/video/how-much-soy-is-too-much/ You may want to search for and watch other videos about soy too.

      re: Nori
      I share your love of nori! That question is harder for me to answer, though. NutritionFacts has a series on iodine that explains that there is a range of iodine that is important to stay within. (Ie, too little or too much and you could be in trouble.) And there is a video which talks about how many sheets of nori you would eat to get enough iodine to meet your daily needs. I think it was 2 sheets.

      The video also warns against some seaweeds which have too much iodine. That’s the main concern I can think of for eating more than the 2 sheets a day. Nori is basically just wonderful greens. And other cultures eat lots of seeweed. So, unless there is an iodine issue (or a contamination issue?), I don’t think you have anything to worry about.

      So, the big question is, does 8 sheets of nori give you too much iodine in a day? I have not done the math myself, but I think you could get the info you need to figure this out from the various videos on NutritionFacts. If you can figure out that 2 sheets is about right in terms of iodine intake, and we know how much iodine is about right, then you could multiply that number by 4 to estimate how much iodine you would get from 8 sheets. Then you could compare the final number to the maximum amount of iodine we are supposed to get in a day.

      One caution about iodine and seaweed: I have read somewhere (I don’t know if this is true or not) that the amount of iodine in commercially sold seaweeds varies dramatically. So, there could potentially be a wide range of iodine in those 8 sheets from brand to brand or maybe? from batch to batch. If you find out that a brand doesn’t have much iodine, then you are golden in terms of your 8 sheets a day. If you find out that a brand tends toward the high end of iodine, then you might have problems down the line.

      I hope these thoughts help you.




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  16. Dr Greger, thanks for your video. I wonder if there’s a mistake in “How not to die” when you state that half of a teaspoon of dulse or arame may get you your iodine for the day (p. 409). You also say that one shouldn’t eat more than 1 tablespoon of dulse or arame everyday (p. 410). You cite the Teas J study (footnote 33 on p. 544). I looked up the study and it does not put USA dulse and arame on the same level when it comes to iodine content (72 mcg per g for dulse, compared to 586 mcg per g for arame). The brand of dulse I have indicates about 165 mcg of iodine per g., equivalent to 1 teaspoon of dulse flakes. Given the above, I’m not sure I understand how (1) half a tsp of dulse can get you your iodine for the day, (2) why having more than a tbsp of dulse would not be advised, and (3) why dulse and arame would be equivalent in terms of iodine. Maybe it’s just something I’m not reading correctly or something I’ve missed. Thanks in advance for the clarification.




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    1. Dear BB2, I am Christine, a NF volunteer moderator. Seaweed is a natural product, and there is always variation in natural products with regard to nutrient content. As you state, Dr. G. writes in the book, “How Not To Die,” that a half teaspoon of dulse or arame on dishes you prepare MAY get you your iodine for the day. I think this is assuming there will be iodine from other sources in the diet as well, and that you will prepare and eat more than one dish per day. If you used a half teaspoon per meal for each of three meals per day, that would likely meet your needs. The key is to shoot for a total from all sources of about 150 mcg per day. It will, of course, take less if the seaweed you use has a higher iodine concentration, and more will be required for a less concentrated source. As Dr. G. states in the book, too much iodine can be as harmful to the thyroid as too little can be. The Institutes of Medicine have set the Tolerable Upper Intake Level (UL) at 1100 mcg for adults. For more concentrated iodine sources, one tablespoon per day could exceed this limit. I hope this helps!




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  17. Hi, I have been vegetarian or vegan for over 20 years now. I consider seaweed to be a healthy part of anyone’s diet. However there are a few factors to consider…
    WHERE does the seaweed come from? This can determine the cleanliness of each type or brand. I would not buy any from china or the west coast usa. Iceland
    is the source of my organic seaweed, nice cold waters ( I believe the KELP is called THORVIN).
    You can add wakame or dulse to soups, stews and so on. Use Arame or Hiziki in salads. Nori to wrap veggie or rice in. KELP powder in smoothies.
    IRISH MOSS in desserts of salads that need to gel.
    EXCESS? I read that somehow excess NORI creates a loss of B-12 in our body so I do not consume more than several sheets a week of this, if that much.
    QUANTITY? I consume seaweed a few times a week, not every day. My dogs loved nori sheets every so often, and I did give them a teaspoon of organic
    KELP powder in their food a few times a week to help their thyroid. namaste’, rachel




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