A Primal Primer: Iodine


Yesterday I mentioned that sea vegetables are a great source of iodine. “But what is iodine?” many emailers asked. Well, dear friends, iodine is elemental. Let’s take a trip through the land of iodine to learn what it is, what it does for the human body and whether you should make an effort to get more iodine in your diet.

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What is Iodine?

Iodine is a highly water-soluble trace element that’s rare in the earth’s crust, but fairly prevalent in its seas. Our bodies require it, for several reasons. Our thyroid glands use it to make thyroid hormones (T3 molecular weight is 59% iodine; T4 molecular weight, 65%), and a severe deficiency can manifest in the development of goiter, which is the thyroid gland swelling up in an attempt to keep up the pace of iodine uptake from the blood and thyroid hormone production. Lovely stuff, eh? Other common symptoms of iodine deficiency include hypothyroidism and hyperthyroidism. It can also increase the incidence of early mental retardation (iodine deficiency-related retardation is the most preventable kind, in fact), and even stunted infant brain development, provided the kid even makes it out alive: iodine deficient pregnant women are at a higher risk for miscarriages and stillbirths.

Today, most table salt has been iodized, and most processed food is in turn made with plenty of iodized salt. As Richard pointed out a few months back, an unintended benefit of the SAD may be the adequate intake of iodine! Ironically, hyper conscious eaters who eschew all processed foods and sprinkle shavings of the purest Himalayan salt blocks (reconstituted, perhaps, from the sweaty pits of organic Sherpas) on their meals may be missing out on iodine. Sea salt does contain trace amounts of iodine, being from the sea, but what’s there degrades pretty rapidly. Subsisting on sea salt alone is almost certainly inadequate for iodine intake. If you avoid processed food (as you should), be sure to eat sea vegetation from time to time.

Iodine Dosage

Iodine dosage is a tricky one to get a handle on. While the RDA of 150 micrograms is sufficient to prevent goiters (kinda like the RDA for vitamin D is enough to prevent rickets), it probably isn’t optimal, and humans can definitely handle larger intakes. After all, coastal-dwelling sorts, like the Japanese, have regularly been consuming iodine-rich sea vegetables for ages without wide-scale thyroid problems – some even suggest this level of intake is preventive against thyroid disorders and breast cancer. Most accounts put them at 5–12mg of iodine daily. The Japanese also consume a fair amount of soy, which has been shown to be antagonistic to iodine uptake, so perhaps they’ve found a balance between the two. At the same time, iodine supplementation can be overdone, leading to hyperthyroidism.

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I lean toward the RDA being short sighted and rather inadequate, to be honest. The tolerable daily upper limit of 1 mg seems better. As they tend to do, the experts cast iodine in a single, solitary role – as the prime regulator of thyroid health and function – and ignore any possibility that it’s important in other realms, too. That’s madness, just like it’s madness to presume vitamin D is only about protecting rickets, even as evidence of its cardio-, immuno-, and carcino-protective effects mount. It’s often stated that the thyroid only needs around 100 micrograms of iodine per day to manufacture sufficient amounts of thyroid hormone and this is used as evidence of the RDA’s accuracy. But only 30% of the body’s total iodine content is concentrated in the thyroid. The rest of it is found in the mammary glands, eye, gastric mucosa, cervix, thymus gland, and salivary glands. If the body is doing something with any sort of consistency, if there’s a pattern to its processes, it’s probably playing an important – even if not entirely understood – role.

Let’s take a closer look at how iodine functions in the human body.

Fetal Development

The fetal thyroid gland begins to function at the 11 week mark of gestation, and at the 18th week, T4 is being produced by the fetus in order to develop its nervous system. The child’s neurological development also depends on proper functioning of the fetal thyroid glands. Sufficient iodine intake (by the mother, of course) is required for sufficient thyroid action in the fetus, just as it’s required in adult thyroids.


After birth, the child still depends on the mother for his or her iodine. Those little brains are experiencing their most rapid period of growth and development, and they need plenty of iodine to avoid impaired cognitive development. Nursing increases the dietary requirement for iodine.

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July 13, 2010