Iodine in milk has skyrocketed since the 1970’s, and that excess iodine could be contributing to thyroid disease. It may be hurting the cows too.
- In 1927, 1 cup of milk had about 14 mcg iodine. (source)
- Today, 1 cup of milk averages 85 mcg iodine. (source)
Milk has become probably the main source of excess iodine in the American diet. You’d have to eat two pounds of fish to get the iodine in just 3 cups of milk now.
Why does it matter?
Because of thyroid disease, which up to 13% of Americans now have. “Excessive amounts of iodide have been linked to the development of autoimmune thyroiditis [thyroid disease] in humans and animals.” (source)
What’s excessive? European food safety regulators say you shouldn’t consume more than 600 mcg iodine per day. (source) That would be a little over 7 cups of American milk today.
A study found that 750 mcg iodine daily caused significant deterioration of thyroid hormone levels.
I personally experienced thyroid dysfunction which greatly improved when I lowered my daily iodine intake, which had been about 720 mcg.
In one study, almost 80% of people were able to cure their thyroid disease by lowering their iodine intake below 100 mcg for several months. More info on that here.
For more details on all this, you can listen to this very informative podcast “How Excess Iodine Is Undermining Thyroid Health” involving a naturopathic thyroid doctor and a regenerative farmer.
Where is all this iodine coming from?
There’s so much iodine in milk because of iodine based disinfectants, and because cows are supplemented with a lot of iodine now. It’s in mineral mixes, concentrate feeds, kelp, iodized salt, and even the non-iodized “gourmet” salt brands sometimes.
Unfortunately, kelp is a big source of excess iodine in milk.
One study fed cows, per day:
- Herbage containing 4400 mcg iodine
- Concentrate feed containing a supplement of 12,800 mcg iodine
- 2 oz kelp containing 75,600 mcg iodine
That was a total of 92,800 mcg iodine, and the cows produced milk with 99 mcg iodine per cup.
These cows were getting so much iodine that their thyroid hormone levels dropped a little at one point, a sign of harm to the thyroid and the cows’ health. (Although this did not happen in other studies.)
How much iodine should be in milk?
The amount of iodine in milk depends on the cow’s diet. If the cow is from an iodine-poor region and not supplemented with iodine, the milk will have too little iodine, and that’s bad. Some iodine is essential, and milk should remain a fairly rich source of iodine. But it shouldn’t be excessive like it is now!
Not being a scientist or dairy farmer, I can’t really say what exactly the iodine content should be, and I can’t say when some iodine or kelp supplementation might be needed. But I have found the following, from 1980 in the USA:
“Historically, the concentration of iodine in milk has been considered to average around 40 mcg/kg. [9.8 mcg per cup] Before 1970, reported concentrations were generally less than 100 mcg/kg [24.4 mcg per cup] and the highest reported value was 165 mcg/kg. [40.3 mcg per cup]” (source)
Cows probably around Aberdeen, Scotland in 1927 had 13.5 mcg per cup. (source) Aberdeen is on the coast so the soil is likely pretty rich in iodine, which is good.
In 2000 in Norway, organic, pasture-raised cows had 14 mcg per cup during the summer, when they’d be eating mostly pasture. (source)
In 1967, cows were considered to be probably iodine deficient when their milk averaged less than 6 mcg per cup. (source)
All in all, it looks like 14 mcg per cup is a good amount.
Stand out from commercial milk!
Pasture raised, chemical free milk from happy cows is extraordinarily good for us. It also tastes much better than commercial milk. Stand out from the industrial milk producers even more by lowering the excess iodine in your cows’ milk!
You can get your milk’s iodine content tested by Michigan State University pretty inexpensively.
If you do lower the iodine in your milk to natural levels, please contact me and I will add your farm to the list of lower-iodine dairy farms on this website.
Who wrote this article?
For the record, I’m not a professional scientist, doctor, or dairy farmer. But I experienced major thyroid health improvement from iodine restriction. I’ve done a fair amount of health research over the years, but I had never heard about the excess iodine in milk (also in eggs, by the way) until I ran across some studies while trying to heal my thyroid.
I also hobby farm pet goats on pasture, though I don’t currently milk them. I strongly support regenerative agriculture and the traditional, natural diet.
My goal with this article is to make regenerative farmers aware of the excess iodine situation, so we can all stay healthy. The increase in iodine seems to be very little known by either health enthusiasts or farmers. I’d like to help change that!
Note: I put this article on my website about endocrine disruptors because excess iodine harms the thyroid and can therefore be considered an endocrine disruptor, as some scientists believe.
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