The Science of Food: Iodine

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   Pacific wakame , a type of kelp with one of the highest iodine content found in foods

Pacific wakame, a type of kelp with one of the highest iodine content found in foods

Dear Readers,

I'm (finally) almost finished reading Goddesses Never Age by Christiane Northrup, M.D. (one of my Top Reads of 2016).  If you can roll with the New Age emphasis, it's a beautiful, uplifting book. I admire Dr. Northrup because she fearlessly goes where few dare to tread when it comes to women's health and self-care.  She's one of the defining voices of her generation in this field: you can see a list of all her books here.  She also has a really nice blog and up-to-date weekly newsletters that I've been enjoying.

One topic that stood out to me from her book (and I've run across this elsewhere recently as well) is the problem many people have getting enough iodine (a trace mineral) in their diets. She writes, 

Still another nutrient that women need is iodine, which helps alleviate breast pain and contributes to healthy hair, nails, and hormone balance. Most women in the U.S. aren’t eating sea vegetables or kelp, which are good sources of iodine.

Dr. Northrup recommends a fairly high guideline of 12.5 milligrams (mg) of iodine per day for most people.  In contrast, the National Institute of Health sets the bar at just 150 micrograms (μg), with 1,000 micrograms equalling 1 milligram, not including additional recommendations for pregnant or breastfeeding women.

Now, there is a lot of debate about how much iodine is enough, and how much is too much.  But won't eating iodized salt take care of most of this dietary requirement, whatever it is?  

Yes and no. Iodized salt was introduced in the US in 1920s in an effort to address a severe iodine deficiency among Americans living in the so-called "goiter belt."  It was an effective solution to goiter, a major public health problem, but the issue remaining today is that the salt used in the production of high-sodium processed and fast food isn't iodized salt.  So even if iodine is cheaply available through salt, it isn't being used in the readily-available fast foods that comprise a large part of the western diet.  Additionally, a 2012 study revealed that nearly 30% of schoolchildren worldwide still lack sufficient iodine in their diets.  

This all points to a need for some iodine supplementation as part of a healthy diet. (Please note: I am not a doctor, and I never offer medical advice. Please consult your healthcare practitioner before starting any new supplements or dietary changes!  It could be very dangerous to your health to make unsupervised changes, depending on what medications you’re on and what preexisting health conditions you may have.) Multivitamins such as the one I use contain iodine: mine has 75 micrograms (μg) from potassium iodide.  As with many key trace minerals, however, iodine is really best absorbed by the body in naturally-occurring forms (whole foods) rather than in synthesized varieties.  

Sea vegetables have some of the highest levels of iodine found anywhere in our diets, but if you look at the packaging of kelp, for example, you probably won't see a little chart detailing exactly how much iodine you'll get per serving. This is because the exact iodine content isn't easy to pin down, even for researchers!  A 2004 study looked at the iodine content of 12 varieties of sea vegetables and found a huge range among the different species.  

Due to this variability in iodine content, the British Dietetic Association actually recommends against eating kelp.  Their May 2016 guidelines state:

Seaweed is a concentrated source of iodine, but it can provide excessive amounts (particularly so in the case of brown seaweed such as kelp) and therefore eating seaweed more than once a week is not recommended, especially during not use seaweed or kelp supplements as an iodine source.

The BDA includes a helpful chart (which can be found on the second page of this handout) detailing other foods from which you can get iodine without the risk of overdosing. Grass-fed organic cow's milk is a good source (provided that the soil of the pasture the cows are grazing on is rich in iodine), as are many varieties of fish, along with pasture-raised eggs. 

I can see where the BDA is coming from with recommending against the use of "kelp supplements," by which I assume they are referring to the powdered varieties available on the market.  If you take an already-concentrated source of iodine and then turn it into a even-more-concentrated powdered form, it would be really easy to blow right through the recommended dietary guidelines, even the high 12.5 milligram (mg) ones set by Dr. Northrup.  

On the other hand, you'll see arguments online for eating large amounts of iodine-containing foods, based on the fact that the Japanese eat one of the highest seaweed-containing diets in the world, and do quite well with their health (for more on the impressive number of Japanese centenarians, The Okinawa Program by Bradley J. Wilcox, et. all (2002) is a fascinating read: I included it in my Top Reads of 2014). However, a 2011 study from the peer-reviewed Journal of Thyroid Research found this issue:

Predicting the type and amount of seaweed the Japanese consume is difficult due to day-to-day meal variation and dietary differences between generations and regions. In addition, iodine content varies considerably between seaweed species, with cooking and/or processing having an influence on iodine content. Due to all these factors, researchers frequently overestimate, or underestimate, Japanese iodine intake from seaweeds, which results in misleading and potentially dangerous diet and supplementation recommendations for people aiming to achieve the same health benefits seen by the Japanese.

The authors concluded that average Japanese iodine intake is closer to 1-3 milligrams (mg) per day, including non-seaweed iodine sources such as fish.  

So what's the "right answer" for the question of iodine intake, whether from kelp or other food sources?  150 micrograms (μg)/day?  3 milligrams (mg)?  12.5 mg?  I'd recommend talking with your doctor to see what he or she recommends for your specific circumstances, particularly if you are pregnant or breastfeeding. Iodine clearly plays a role in a healthy diet...the question is still how much is right for you, though. 

Here in our kitchen we like to add iodine into our diet periodically by sprinkling about 1-2 tsp. of dried kelp into a pot of brown rice, right at the beginning of the cooking process.  We don't stir it in, but just let it sit on top of the rice as it cooks.  As you can imagine, kelp flavors the rice pretty strongly, so this method works best when the rice is being served as a side for seafood.  

Cooking with kelp helps fill our iodine needs naturally, since we like to use Celtic sea salt instead of iodized salt (and you'll see I call for it in my recipes too). Celtic salt has a very small amount of naturally-occurring iodine, but not enough to be significant in our diet.  It tastes great, though, and does contain small amounts of other trace minerals.  We also drink organic milk (non-homogenized) as well as taking the multivitamins I mentioned earlier.  Additionally, we try to work fish into our diet as often as possible, particularly wild-caught Pacific salmon and my favorite, Wild Planet canned sardines. 


Yours Scientifically,


P.S. This article has a lot of links, many to products you can buy.  As usual, I am not a product representative for ANY brand, and receive no benefits (monetary or otherwise) from sharing these on my site. I am in no way affiliated with, and any products/brands I write about or link to on that site (or any other) are included just because I like them enough to share with my readers.