Have you ever seen something called "iodized" salt at the grocery store and not known what it was? I recently had someone tell me that they do not buy iodized salt because they assumed it was more processed and therefore not as healthy. Yes, it is true that iodized salt is more processed, but in a good way!
The Relationship between Iodine and Thyroid Health:
Iodine is a mineral that is essential for thyroid function. The thyroid is a gland located in your neck that secretes hormones that directly affect several body functions (1,2):
metabolism
body temperature regulation
growth and development
fertility
cardiovascular function
The two hormones that the thyroid produces are triiodothyronine (T3) and thyroxine (T4), and iodine is one of the main components of both of them (3). If there is not enough iodine available, your body cannot make sufficient amounts of these two hormones. In fact, the leading cause of thyroid disorders in the world is iodine deficiency (In the United States, the primary cause of thyroid disorders are autoimmune diseases and not iodine deficiencies, largely because of the use of iodized salt) (1).
Sources of Iodine:
Iodine is found in the soil and in sea water, and while crops are able to absorb iodine from the soil, they are not the most reliable sources of this trace mineral because the amount of iodine in the soil differs by region (4). If a crop is grown in an iodine depleted area, the crop will not contain much iodine, and therefore the people or animals consuming the crop will not be getting much iodine from their food. In other words, the same type of food grown in two different places may have vastly different iodine concentrations. Even if you live in an area that has a plentiful amount of iodine in the soil, you may not be getting enough iodine directly from your food because so few of us actually eat 100% local food.
Seafood (both fish and sea plants such as sea weed) is a little bit better source of iodine because marine animals and plants are able to concentrate the iodine from the water around them (4). Dairy foods such as milk also contribute some iodine because the mineral is often added to cattle feed (2). However, one of the greatest contributors of iodine to the typical American diet is iodized salt.
Iodine Deficiency:
Iodine deficiencies can lead to a variety of conditions such as goiter (an enlarged thyroid gland), hypothyroidism (low levels of thyroid hormones which can cause reduced metabolism, inability to regulate body temperature, fatigue, cardiovascular disease, and more) (1), reduced fertility, increased rates of miscarriages, and can even lead to developmental issues and neurological disorders in children born from mothers who are deficient in iodine (5). The World Health Organization actually calls iodine deficiency the leading cause of preventable brain damage (6).
Iodine deficiencies were extremely common in the United States and other areas of the world before the mid-1900s. In order to reduce the prevalence of iodine deficiency and thyroid disorders, the food industry began fortifying salt with the trace mineral in 1924 (2), creating “iodized salt.” Since then, iodine deficiency in the United States and other countries that fortify their salt have decreased substantially. In 2007, one study showed that North and South America had the lowest incidence of iodine deficiency (only about 11%) compared to other areas in the world as well as the highest number of households using iodized salt (approximately 90%) (4). Many countries have made it mandatory for salt to be iodized due to its efficacy in reducing deficiencies, but iodization is optional in the United States (7).
Products such as sea salt, Himalayan salt, kosher salt, and others are not fortified with iodine, and the trend to use more of these specialty salts may reduce overall iodine intake and increase the risk for deficiency (however, these salts do contain other beneficial minerals) (8).
The Takeaway:
Now does this mean that you should load up on additional salt on all of your food? No! Thankfully, the recommended amount of iodine is only 150 micrograms per day, which is a really, really small amount. One teaspoon of iodized salt provides more than the needed amount of daily iodine (5). And in fact, having too much iodine can cause just as many problems as not having enough (not to mention the effects of excess sodium on blood pressure)!
The main takeaway here is to not avoid iodized salt at the grocery store. If you want to have some of the specialty salts on occasion, then by all means, go for it! However, when it comes to your traditional “table salt,” I would recommend going for the iodized version unless you have a specific medical condition or take medications that put you at risk for iodine toxicity. Resources:
Chiovato L, Magri F, Carlé A. Hypothyroidism in Context: Where We’ve Been and Where We’re Going. Adv Ther. 2019;36(Suppl 2):47-58. doi:10.1007/s12325-019-01080-8
Janice L. Thompson, Melinda M. Manore, Linda A. Vaughan. The Science of Nutrition. 3rd ed. Pearson Education; 2014.
Information NC for B, Pike USNL of M 8600 R, MD B, Usa 20894. How Does the Thyroid Gland Work?Institute for Quality and Efficiency in Health Care (IQWiG); 2018. Accessed May 31, 2021. https://www.ncbi.nlm.nih.gov/books/NBK279388/
Zimmermann MB. Iodine Deficiency. Endocrine Reviews. 2009;30(4):376-408. doi:10.1210/er.2009-0011
Iodine Deficiency. American Thyroid Association. Accessed May 31, 2021. https://www.thyroid.org/iodine-deficiency/
WHO | Micronutrient deficiencies. Accessed June 3, 2021. https://www.who.int/nutrition/topics/idd/en/
Micronutrients I of M (US) P on. Iodine. National Academies Press (US); 2001. Accessed June 3, 2021. https://www.ncbi.nlm.nih.gov/books/NBK222323/
KC Wright. Update on Iodine. Today’s Dietitian. 2018;20(12):24.