Why is iodine first in this chapter? Not only is it the only non-B vitamin in this chapter, but there is also a connection between selenium (last antioxidant in the previous chapter) and iodine. Iodine's only, yet critical, function is that it is required for thyroid hormone synthesis. The figure below shows that the thyroid gland is a butterfly-shaped organ found in the neck. The parathyroid glands are also found within the thyroid gland.
Figure 10.11 Location of thyroid and parathyroid glands1
Iodine is found in foods primarily as iodide (I-), some bread dough has iodate (IO3-) added to help with gluten cross-linking2. This used to be more commonly used in the past than it is now. Like selenium, iodide concentrations of the soil vary greatly, causing food concentrations to greatly fluctuate. Sea water is high in iodine, thus foods of marine origin, such as seaweed and seafood, are good dietary sources of iodine. Dairy products also tend to be good sources of iodide because it is added to cattle feeds. Cattle receive iodine-containing medications, and iodide-containing sanitizing solutions are used in dairy facilities3,4.
For most Americans, we consume ample iodine through the consumption of iodized salt. Consumption of 1/2 teaspoon of iodized salt meets the RDA for iodine. There is a global logo for iodized salt. However, I must admit that I don't recall ever seeing it myself.
The other link below is to a page that contains a scorecard map that depicts access to iodized salt worldwide. It also contains a Youtube video that displays the reduction in iodine deficiency over the last 2 decades.
Salt is iodized with either potassium iodide (KI) or potassium iodate (KIO3). The positives of each are:
- Potassium iodide
- + Less expensive
- + Higher iodine content (76% vs. 59% for KIO3)
- + More soluble
- Potassium Iodate
- + More stable
The U.S. uses potassium iodide, but the form, and amount used varies from country-to-country. Most Americans’ salt intake comes from processed foods, many of which are made with non-iodized salt. Iodine is well absorbed (~90%). Some dietary compounds interfere with thyroid hormone production or utilization. These compounds are known as goitrogens5. However, it is not believed that goitrogens are of clinical importance unless there is a coexisting iodine deficiency5.
Some examples of foods that contain goitrogens are3,4,6:
Figure 10.12 Cassava plants are typically grown in tropical and subtropical environments6
Figure 10.13 The cassava roots are what are typically eaten, but first they must be peeled. These are unprocessed7
Figure 10.14 Peeled cassava roots8
Figure 10.15 Millet growing in a field9
Figure 10.16 Millets10
Cruciferous Vegetables (broccoli, cabbage, Brussels sprouts)
References & Links
- Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
- Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw's perspectives in nutrition. New York, NY: McGraw-Hill.
- Whitney E, Rolfes SR. (2008) Understanding nutrition. Belmont, CA: Thomson Wadsworth.
- Anonymous. (2001) Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, D.C.: National Academies Press.
Global Iodized Salt Logo - https://en.wikipedia.org/wiki/File:G..._salt_logo.jpg
Global Iodine Scorecard - http://www.ign.org/scorecard.htm