Iodine and thyroid health

Iodine is a mineral, also known as a trace element. It’s an essential part of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Iodine is also important for the proper functioning of your immune system (1, 2).

Iodine is mostly present in a form of sodium and potassium salts (2). Recommended dietary allowance (RDA) of iodine for people 18 years and older is 150 micrograms (mcg), and 220 mcg during pregnancy (2).

Best food sources of iodine (3):

• Fish
• Cheese
• Eggs
• Milk
• Berries
• Seaweed
• Bread

Foods with small amounts of iodine from natural sources can be fortified to have more iodine — like salt, infant formulas, and meal replacements (4).

Iodized salt is a common source of iodine used in home cooking. Most commercial vendors don’t use iodized salt, although some commercially prepared breads and pizzas contain high concentrations of iodine if iodates are used as dough conditioners (4).

Research suggests that consuming iodized salt is effective in improving iodine levels. However, there are variations in the amount of iodine in these salts — this is due to techniques used for salt iodization, as well as storage conditions. Research studies still haven’t addressed the many of the possible side effects of iodized salts (5).

Iodine deficiency

Being deficient in iodine has many health effects — it permanently impacts growth and development before birth and it’s the most common cause of preventable mental retardation worldwide (6).

An inadequate dietary intake of iodine leads to insufficient thyroid hormone production. This affects many parts of the body, particularly the heart, developing brain, liver, kidneys, and muscles.

Other symptoms include impaired mental function and decreased ability to concentrate on a specific task.

People living in river valleys prone to flooding and mountainous areas — such as the Alps, Andes and Himalayas — are at the highest risk of suffering from iodine deficiency (4). Soy, cassava, cabbage, broccoli, cauliflower, and other cruciferous vegetables contain substances (goitrogens) that interfere with iodine activity. Consuming high amounts of these foods might increase your risk of being iodine deficient (2, 7).

Iodine overdose

Intaking too much iodine might cause similar effects as iodine deficiency, such as swelling of the thyroid gland (goiter), elevated TSH levels, and hypothyroidism (8).

Acute iodine poisoning is rare, symptoms include (2):

• Burning of the mouth, throat, and stomach
• Fever
• Abdominal pain
• Nausea
• Vomiting
• Diarrhea
• Weak pulse

Iodine and hypothyroidism

The thyroid gland needs iodine for its day-to-day functioning. It gets it from blood plasma in a process called iodine trapping. In order to trap enough iodine, thyroid cells need to repeatedly filter blood plasma. TSH levels will be balanced if there is enough blood plasma (9, 10). However in the case of iodine deficiency, the thyroid will not be able to produce T4 and T3, which will cause an increase in TSH levels (6).

An enlarged thyroid gland (goiter) is one of the first signs of iodine deficiency and hypothyroidism (2). Goiter happens when the thyroid gland tries to cope with iodine deficiency by increasing the speed and amount of plasma filtered. In order to do this, the thyroid gland needs more cells to filter blood plasma — so the thyroid grows and enlarges.

Before deciding on any type of supplement you should talk to your doctor about possible side effects of iodine, especially used in combination with other medications and supplements.

How we write: our information is based on the results of peer reviewed studies using the National Library of Medicine platform. It is written by scientists and reviewed by external experts. If you believe we might have overseen crucial scientific information, please contact us at hello@boostthyroid.com

Disclaimer: This information is not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you want to change your treatment, lifestyle, your diet, include supplements in your diet or have concerns about your health, please consult your doctor before trying new approaches.

References

1. Chung HR. Iodine and thyroid function, 2014
2. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc, 2001
3. Carlsen MH, et al. New Iodine Food Composition Database and Updated Calculations of Iodine Intake among Norwegians, 2018
4. Pehrsson P, et al. Iodine in food- and dietary supplement–composition databases, 2016
5. Clar C, et al. Iodized salt for iodine deficiency disorders. A systematic review, 2002
6. International Council for the Control of Iodine Deficiency Disorders. Iodine Deficiency Disorders, 2020
7. Zimmermann MB. Iodine deficiency, 2009
8. Hess SY. The impact of common micronutrient deficiencies on iodine and thyroid metabolism: the evidence from human studies, 2010
9. Pennington JA. A review of iodine toxicity reports, 1990
10. Jameson JL, et al. Endocrinology adult and pediatric: the thyroid gland, 2013