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Iodine 101: Testing, Top Foods, and Supplements

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Iodine 101: Testing, Top Foods, and Supplements

Iodine is an important trace mineral that is essential for human health. Iodine deficiency is the leading cause of preventable brain damage in newborns and infants worldwide. Adequate levels are vital for optimal function throughout the body. It is specifically necessary for thyroid physiology. This article will discuss what iodine is, how it affects the body, how to test for it, and how to ensure proper levels.


What is Iodine?

Iodine was first discovered in the 1800s by French chemist Bernard Courtois. Courtois was making gunpowder when sparks of a violet substance, what we now know as iodine, emitted. The name "iodine" comes from the Greek word ioeidēs, which means purple.

Iodine is a trace mineral essential for human health; however, we do not innately make it. Iodine is found in soil. Soils contain iodine levels that will penetrate into crops, thus supplying us with iodine. However, there are many areas of iodine soil depletion. Because of this, iodization programs have been implemented in many countries to avoid iodine deficiencies. Iodization programs involve enriching the food supply with iodine, primarily through iodized salt.

What is Iodine's Role in The Body?

Iodine is a requirement for proper thyroid functioning. The pituitary gland releases thyroid-stimulating hormone (TSH). TSH keeps levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) steady, inhibiting high levels that can cause hyperthyroidism and low levels that can cause hypothyroidism. TSH release causes iodine to be taken up by the thyroid for use in the creation and release of T4 and T3.

Iodine deficiency typically occurs when a person receives less than 20 micrograms (mcg) of iodine daily. Lack of iodine can cause the thyroid gland to become enlarged, referred to as a "goiter." The enlargement is the thyroid's way of trying to catch and keep more iodine from the circulation to make thyroid hormones. Additionally, in a state of iodine deficiency, T4 and T3 are not readily made, and TSH will remain elevated, causing hypothyroidism. Hypothyroid symptoms can include fatigue, weight gain, cold intolerance, hair loss, constipation, brain fog, low libido, depression, and more.

People who do not use iodized salt, pregnant women, people who do not consume meat, dairy, seafood, and eggs regularly, and people who live in areas with iodine-deficient soil may be at risk for low iodine levels. Additionally, people with lower iodine levels but who consume high amounts of goitrogen-containing foods are also at risk. Goitrogens are substances that inhibit the uptake of iodine by the thyroid gland. Common goitrogen-containing foods include cassava, soy, and cruciferous vegetables, including broccoli, kale, and cabbage.

Excess iodine can occur due to over-supplementation, consumption of certain medications, and excess amounts of iodized salt in the diet. High amounts of iodine can produce too much thyroid hormone and lead to hyperthyroidism. Hyperthyroid symptoms include rapid heart rate, weight loss, heat intolerance, anxiety, and hair loss. Extremely high amounts can lead to iodine toxicity and result in burning in the mouth and throat, excess saliva production, brassy-like taste in the mouth, fever, nausea, vomiting, acne-like breakouts, and may eventually lead to low pulse, airway swelling, and coma.

However, high amounts of iodine can also lead to goiter and hypothyroidism.

Excessive iodine may also cause an autoimmune reaction to occur against the thyroid gland, and high iodine levels may also trigger thyroid cancer. Lastly, excess iodine can lead to the Wolff-Chaikoff effect, where the thyroid rejects high amounts of iodine and thus leads to low levels of thyroid hormones.

Because of its effects on thyroid physiology, iodine is especially important for pregnant women and infants, as a lack of iodine can lead to irreversible brain damage in these populations. Iodine deficiency in pregnant women can result in fetus growth and development problems, miscarriage, and stillbirth. Additionally, iodine deficiency can cause cretinism, a condition that includes cognitive disabilities, stunted growth, deaf mutism, delayed sexual development, and other neurological and physical changes.

Additionally, mild iodine insufficiency in pregnant women increases the risk of attention deficit hyperactivity disorder (ADHD) in children, and iodine deficiency in children can result in lower IQ and other neurodevelopmental deficits.

How to Test Iodine Levels

Testing for iodine deficiency will differ from testing for iodine excess. Iodine deficiency is best checked by doing a 24-hour urine sample. This is because iodine levels will fluctuate throughout the day; thus, one sample may be misleading. An AM and PM dried urine sample may also be used to check iodine levels and may be easier for the patient as opposed to the 24-hour collection. It is important to monitor or be aware of large intakes of iodine while testing occurs, as 90% of the iodine in the diet will end up in the urine.

A blood test is preferred in cases of suspected high iodine levels, as it is quicker than a 24-hour urine or dried urine test, and the results of excessive iodine can be an emergency.

Additional labs, including a full thyroid panel and ultrasound, may also be indicated to fully assess iodine levels by having a complete picture of thyroid functioning. Autoimmunity may result in the case of high iodine, and thus thyroid antibodies should also be checked.

How to Make Sure You are Getting Enough Iodine in Your Diet

The Recommended Daily Allowance (RDA) is the daily intake needed to meet nutritional requirements. The RDA for iodine is dependent upon age:

Additionally, pregnant and lactating women require higher intakes of iodine. The RDA for pregnant women is 220 mcg, and the RDA for lactating women is 290 mcg.

Due to a lack of evidence, there is no RDA for children under one year old. However, levels of Adequate Intake (AI), a measurement indicating an amount of vitamin or mineral assumed to give sufficient nutrient status, have been established for those under one year old. The AI from birth to six months is 110 mcg, and the AI from seven to 12 months is 130 mcg.

Iodine can be found naturally in certain foods and can also be found in processed foods due to the introduction of iodine fortification in the food system.

Foods Naturally High in Iodine

Processed Foods High in Iodine



Iodine is imperative for human health due to its effects on thyroid physiology. Lack of iodine or excessive amounts of iodine can result in significant negative effects on the thyroid, which in turn will affect the entire body. Iodine is of utmost importance in pregnant women and children, as a lack of iodine can lead to irreversible damage. Iodine testing can be beneficial for those concerned about low or excessive levels and can help to understand why thyroid physiology may be malfunctioning.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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