Iodine & Health
What is Iodine & What Does it Do?
Iodine is a non-metal mineral that is essential for our health. It is found in the soil and seawater, and its main function is making thyroid hormones. You may have heard your doctor talk about T3 and T4, these are two of the hormones made by our thyroid gland. The numbers tell us how many iodine molecules are attached: T4 = four iodine molecules and T3 = three iodine molecules. Pretty handy naming there!
I could wax on about thyroids here, but I’ve already done that! If you would like a thyroid refresher, please check out last year’s article: Healthy Thyroid Function.
This week, we will look at iodine, and the best way to understand its importance is to see what happens when you don't get enough.
Iodine Deficiency:
One of the easiest to see signs of iodine deficiency is a goiter. A goiter is a swelling in the neck that is made up of an enlarged thyroid gland. We see this in cases of iodine deficiency, hyperthyroidism (too much thyroid hormone production), thyroid cancer, and sometimes in autoimmune thyroiditis (Hashimoto’s disease). In iodine deficiency, this swelling is our body’s way of trying its best to keep us alive!
When there isn’t enough thyroid hormone in our circulation, our pituitary gland will keep asking our thyroids to make more hormones. The problem in iodine deficiency is in the final step - there isn’t enough iodine to finish making the hormone. All this activity with no finished end product results in swelling of the thyroid gland itself. A goiter can cause voice changes and difficulty with swallowing and breathing. In addition to this swelling in the neck, iodine deficiency also causes problems through the rest of the body.
With iodine deficiency, we also see a decrease in circulating thyroid hormone which results in hypothyroidism (not enough thyroid hormone production). For adults, this will cause a complex constellation of symptoms involving decreased body temperature, low energy levels, slowed digestion, and slower cell growth and repair. For a fetus or infant, the effects can lead to birth defects, stunted growth and development, and mental retardation. (1)
Those at increased risk of iodine deficiency include:
People in areas where soil levels of iodine are low
Pregnant people
Fetuses
Nursing infants
People eating packaged weight-loss foods
Those who do not eat seafood, seaweeds, or iodized salt
Where to Find Iodine:
Iodine is available as a supplement usually in the form of potassium iodide. It is commonly found in multivitamins, so a separate supplement is rarely recommended. Some table salt is also fortified with iodine. In the United States, this salt fortification is voluntary, but it is mandatory in some countries, such as Canada. Processed foods, which tend to be where the majority of US residents consume their salt, mostly do not include iodized salt.
When it comes to food, seafood and seaweeds tend to be great sources of iodine, as they are able to concentrate the mineral from salt water. Dairy products are another common source of iodine in the U.S. Eggs, fruit, grains, and some beans also contain variable amounts of iodine depending on where they were grown.
When it comes to foods grown on land, the iodine status of the soil will determine how much iodine is found in the final food product. In soils that have been stripped of their minerals by erosion – whether due to natural causes or excessive tilling and monocropping – iodine levels tend to be quite low, and goiters are much more common. We see this in mountainous regions like the Andes, flooded river valleys like the Ganges river plain in India, and inland regions such as the Midwestern United States. (1)
Daily Intake:
The recommended daily allowance (RDA) for iodine is 150 mcg for adolescents and adults. Pregnant individuals are advised to increase their intake to 220 mcg and those who are nursing are urged to aim for 290 mcg. These amounts are the recommendation to avoid iodine deficiency and the resulting complications. The Linus Pauling Institute holds to these recommendations as “there is presently no evidence that iodine intakes higher than the RDA are beneficial.” (1)
To put this into perspective, one cup of cow’s milk contains around 90 mcg of iodine, a 3 oz serving of cod contains around 99 mcg of iodine, and a ¼ ounce of dried seaweed can contain around 4500 mcg of iodine!
Prevention of Disease:
Looking at the information above, we can begin to appreciate how important iodine is. Keeping adequate levels of iodine in one’s diet can prevent the development of iodine deficiency and its related problems, but can supplementing extra iodine prevent any additional issues?
So far, the answer appears to be no. Research into supplementing more iodine than the RDA during pregnancy and infancy shows “no evidence of improved growth or neurodevelopmental outcomes in infants.” (2) Another meta-analysis study shows that supplementing extra iodine isn’t recommended during lactation or infancy in areas without iodine deficiency. (3) A review of the research shows that most iodine supplementation studies focus on pregnancy and infancy at this point.
As always, if you are recommended to take iodine or any other supplement as a preventative treatment for another condition, look for the research to understand where this recommendation is coming from and be sure to discuss it with the members of your healthcare team who are trained in nutrition and the disease you are looking to prevent.
Disease Treatment:
What happens if you already have a diagnosis? Is there any good evidence for the use of iodine to treat specific diseases?
You may read about using iodine in the treatment of fibrocystic breast disease. I too heard about this in medical school. Unfortunately, the research doesn’t support the use of iodine in fibrocystic breast disease. (1) The doses used to slow or stop cell growth in petri dishes would end up creating toxicity in humans. So theoretically, you could use iodine to slow fibrocystic growths in breasts, but you may end up suffering from iodine toxicity instead.
Toxicity:
Iodine toxicity is rare, but is possible with doses of several grams. These symptoms include “burning of the mouth, throat, and stomach, fever, nausea, vomiting, diarrhea, a weak pulse, cyanosis, and coma” (1)
However, what is more common is excess iodine intake creating problems with thyroid function. When iodine deficiency is treated too aggressively, thyroid function can increase rapidly and hyperthyroidism (excessive thyroid hormone) can occur. In those with normal thyroid function and iodine status, excessive iodine consumption can trigger hypothyroidism (too little thyroid hormone).
Due to these very real consequences, an upper level for iodine intake has been set at 1,100 mcg per day for adults and lower for children. (4)
Medication and Nutrient Interactions:
There are a few medication interactions to consider when it comes to iodine: (1)
Amiodarone, which is used to control heart rate, contains high levels of iodine, and increased iodine intake may make the medication effects stronger.
Drugs used to control hyperthyroidism may interfere with iodine function and lead to hypothyroidism in the long run.
Lithium, used long-term, can interfere with iodine metabolism leading to hypothyroidism.
High-dose potassium iodide supplementation can also decrease the activity of warfarin, which is used to prevent blood clotting.
Applications:
Our takeaways this week are:
Iodine is an essential nutrient for life and is mainly active in the creation of thyroid hormones.
Iodine is found in the soil and in sea water. Some soils have been stripped of iodine due to erosion from natural or man-made activities, and iodine deficiency is more common in those areas.
Iodine deficiency leads to goiter and hypothyroidism.
Supplementing above the RDA does not have any benefits supported by research.
Too much iodine can lead to impaired thyroid function.
If you are being treated with amiodarone, medications to control hyperthyroidism, warfarin, or long-term lithium, it’s a good idea to talk with your healthcare team about your iodine needs.
Next week:
Next week we will investigate iron.
To our health!
References:
Higdon, J, “Iodine” Linus Pauling Institute, 2000; last update: 2015; accessed December 13, 2021; https://lpi.oregonstate.edu/mic/minerals/iodine
Nazeri P, Shariat M, Azizi F. Effects of iodine supplementation during pregnancy on pregnant women and their offspring: a systematic review and meta-analysis of trials over the past 3 decades. Eur J Endocrinol. 2021 Jan;184(1):91-106. doi: 10.1530/EJE-20-0927. PMID: 33112293.
Nazeri P, Kabir A, Dalili H, Mirmiran P, Azizi F. Breast-Milk Iodine Concentrations and Iodine Levels of Infants According to the Iodine Status of the Country of Residence: A Systematic Review and Meta-Analysis. Thyroid. 2018 Jan;28(1):124-138. doi: 10.1089/thy.2017.0403. PMID: 29334343.
Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001. 8, Iodine. Available from: https://www.ncbi.nlm.nih.gov/books/NBK222323/