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February 21, 2010 7:28 PM   Subscribe

Question about seaweed, iodine (deficiency and overconsumption), and thyroid changes

I recently decided to make sushi for the first time, and along with that, re-discovered my love of snacking on plain nori (my parents were health nuts as a child, and as a result my favorite snack as a kid was snacking on sheets of nori. weird i know).

I haven't snacked on nori sheets since being a kid, but am finding again that I love the taste, texture, and idea of snacking on something "healthy" and very low calorie. But the package of nori said that one sheet contained about 90% of the daily recommended allowance of iodine.

But I also noticed that within a couple of days of my nori-snacking, my mood began to improve. I started feeling better, more energetic, and hopeful, when nothing else really changed. My guess is that my thyroid was functioning low prior, and the iodine > thyroid > mood link revved it up.

I generally eat quite conscientiously - eat my fruits and veggies, lean meats on occasion (once, maybe twice a week), I cook and don't eat out very often. We do have iodized salt in the house, but I don't use it often and only salt dishes to the point of necessity (I salt occasionally when cooking, hardly ever on the plate). And I kind of forgot about iodine in the list of necessary vitamins and minerals, so I think my diet was unconsciously lacking in iodine.

Anyway. At what levels would too much iodine be? At what point does iodine consumption become risky and dangerous, leading to thyroid complications (and cancer!)? Should I cut back and re-introduce increased iodine much more gradually?

I like nori and would eat more if I didn't think it would be dangerous. How much nori would be too much?
posted by jalebi to Health & Fitness (6 answers total) 8 users marked this as a favorite
According to the MSDS for potassium iodide:

ORL-MUS LDLO 1862 mg kg-1

ORL = oral
MUS = mouse
LDLO = lowest published lethal dose

So in mice, the lethal dose is about 1.8 grams of potassium iodide per kilogram of body weight in mice. That's about twice as poisonous as table salt, for which equivalent figure is 4000 mg/kg.
posted by Chocolate Pickle at 9:10 PM on February 21, 2010

A couple quick searches shows:

"The RDA for iodine is 150 mcg. Ingestion of up to 20 times the RDA has no known side effects. Side effects of 30 times the RDA may include mouth sores, metallic taste, swollen salivary glands, diarrhea, vomiting, headache, rash, and breathing difficulties."

"The World Health Organization places the safe upper limit of iodine intake at 1000mcg per day for adults.

A mcg is a microgram. 1/millionth of a gram.

Nori has a pretty low level of iodine compared to other seaweads (Kombu has 2500 mcg/gm): Nori 16 mcg/gm. An 18×20 cm sheet is about 3 grams, so you'd have to eat about 3 sheets to get to the RDA level, 20 sheets to get to the WHO upper limit, and you'd probably be OK up to 60 sheets. There are typically 4-6 strips/sheet.

"too much" nori then would be over 240-360 strips per day.

Sorta a lmgtfy question, but I saw a bunch of people have fav'd this, so hope that helps.
posted by lhl at 9:11 PM on February 21, 2010

I had to go on an low-iodine (below 50mcg per day) diet while in treatment for thyroid cancer. It's really, really difficult. Unless you are a raw food vegan, I doubt that you have an iodine deficiency. Pretty much anything that has salt in it probably has iodine in it. Anything from the sea (like your nori, or seafood) has iodine in it. Some red dyes have iodine. Dairy product have iodine. Soy beans, egg yolks... if you are eating these things, then you probably get enough iodine.
posted by kimdog at 6:19 AM on February 22, 2010

I snack on nori like crazy as well. I did some research and apparently too much iodine can cause both hypo and hyper thyroidism. I would be aware of the symptoms of both, but also remember that people have been eating seaweed...and large amounts of it, for a very long time without problems, the modern environment and diet contains a lot of nutrients that compete with iodine like bromine, and the people in these studies were often eating seaweed for breakfast, lunch, AND dinner.

Nori also is one of the seaweeds with higher levels of bromine than iodine. And yeah, bromine supposedly cancels out some of that iodine, so nori isn't even one of the recommended seaweeds for iodine deficiency.

But remember most salt in the US is iodized, so if you are eating something salty at a restaurant you might be getting too much iodine. But iodine deficiency has reemerged as a problem in developed countries despite iodized salt. And hypothyrodism also has increased.

I also notice that I only crave seaweed in cold weather and since I've been eating it I've had less sensitivity to cold.
posted by melissam at 7:04 AM on February 22, 2010 [1 favorite]

How much is too much depends entirely on your own body. Those who are free of susceptibility to thyroid conditions don't have to worry about eating too much iodine in their food.

However, anyone who is susceptible to autoimmune thyroid conditions, such as Hashimoto's-type hypothyroidism, or hyperthyroidism, may find their disease to be triggered or exacerbated by an average iodine intake much above 100% of the US RDA (150 micrograms per day). My endocrinologist told me that none of my blood relatives should consume more than this amount on a regular basis, because anyone who is related to someone with autoimmune thyroid disease may have more than the average risk of these diseases. He advised me not to give iodized salt to my children. It seems likely that the high rate of autoimmune thyroid disease in developed countries (as many as 10% of the population, by some estimates), is caused by the very high intake of iodine, which is commonly well above the recommended daily amount. Given that thyroid disease is usually treatable, I think it's a reasonable price to pay for avoiding cases of mental retardation in children caused by iodine deficiency, which are common in landlocked countries that lack iodine supplementation in their food supplies.

It is difficult in developed countries to consume an inadequate amount of iodine. Of course seafood, seaweed, and iodized salt are all good sources of large amounts of iodine. Surprisingly, dairy products are also a good source of iodine, because iodine is popular for use as a disinfectant for the udders of cows, before milking, and store-bought bread can also be a rich source of iodine. In the US, your entire RDA of iodine can often be found in a single cup of milk, and in some cases in just half a slice of bread. (ref) In fact, any food you buy that has salt added to it, such as breakfast cereal or soup, will often be made with iodized salt, without any mention of iodine on the label. Even if you never salt your food yourself, it's unusual in developed countries to have anything but a higher-than-recommended intake of salt, from grocery-store items and occasional restaurant food. And, of course, it is difficult to find any multivitamin pill that does not itself contain a full 150 micrograms of iodine by itself.

Keep on eye on your thyroid function over time. If in fact your recent high intake of iodine is affecting your thyroid, when you were almost certainly not iodine deficient before, it might be due to a thyroid problem, in which case you might find that you develop hypothyroidism at some point in the the future. If so, your high intake of iodine will eventually cease to appear to help you, because the long-term effects of high iodine intake on autoimmune thyroid disease are negative.
posted by Ery at 7:52 AM on February 22, 2010 [2 favorites]

It is difficult in developed countries to consume an inadequate amount of iodine.
This depends heavily on where you live. I believe that it is true in the US because the soil is rich in iodine so all plant foods contain a bit and that adds up. Where I live (Netherlands) it is easy to get not enough iodine if you do not drink milk and bake your own bread with sea salt or other non-iodized salt. Milk, fish and iodized salt are the only real sources of iodine here.

My daughter likes to snack on nori (no idea why!) and I researched the iodine thing too. I found the same thing lhl says: nori is not that high in iodine.
posted by davar at 11:50 AM on February 22, 2010

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