Iodine is a naturally occurring mineral required for thyroid hormone production and fetal growth and development. Although uncommon in North America, iodine deficiency can occur in certain populations, particularly individuals who don’t regularly consume iodine-rich foods, as well as pregnant or breastfeeding individuals. (9)
Consuming too little or too much iodine can wreak havoc on your health. (9) Keep reading to learn more about the importance of iodine, how much you need, and the best dietary sources.
What is iodine?
Iodine is a trace element found in some foods, iodized salt, and dietary supplements. It’s considered an essential mineral, meaning that the body cannot produce it and you must obtain it from your diet or supplements. (1)(9)
Iodine is largely responsible for optimal thyroid hormone production. The thyroid is a butterfly-shaped gland that lies at the base of the neck. The hormones produced by the thyroid depend on sufficient iodine intake and influence various bodily functions such as body temperature, respiration (breathing), heart rate, and digestion. (9)
How much iodine do you need?
Consuming various foods containing iodine can help you reach your daily needs. The Recommended Dietary Allowance (RDA), the average daily amount of iodine sufficient to meet the needs of most healthy individuals, is outlined in the table below.
Dietary sources of iodine
Iodine can be found in various food sources, particularly sea vegetables, dairy products, and salt fortified with iodine.
Did you know? Many countries add iodine to table salt. Since adopting this public health measure, rates of iodine deficiency have significantly declined worldwide. (9)
Top iodine benefits
Consuming enough iodine through diet, or supplementing your diet with iodine when directed by your practitioner, is essential for maintaining various bodily functions. Iodine is best known for its thyroid health benefits; however, a large body of evidence also demonstrates that iodine supports fetal growth and development and also promotes healthy breast tissue. (9)
1. Thyroid function
The thyroid gland produces thyroid hormones, thyroxine (T4) and triiodothyronine (T3), which help regulate numerous bodily functions, such as metabolism, growth, and development. (4) The thyroid cannot synthesize (produce) optimal levels of thyroid hormones without enough iodine. (8)
When the body doesn’t get enough iodine, the hypothalamus (a gland in the brain) increases secretion of thyroid-stimulating hormone (TSH), a hormone that stimulates the thyroid gland to produce T3 and T4. Elevated levels of TSH can cause enlargement of the thyroid gland, also known as a goiter. Consuming less than 50 mcg per day of iodine may increase your risk of developing a goiter. (5)(9)
Long-term iodine deficiency may also lead to a deficient supply of thyroid hormones, a condition known as hypothyroidism. (5)(9) On the other hand, consuming too much iodine can lead to an overactive thyroid, also known as hyperthyroidism. (11) Reaching the RDA for iodine and only supplementing with iodine when clinically necessary is an effective strategy for maintaining normal thyroid function.
Did you know? Iodine deficiency is the primary cause of preventable thyroid disorders. (12)
2. Fetal growth and development
Adequate iodine intake during pregnancy is critical for healthy fetal development. During pregnancy, iodine requirements rise to support the increased demand for maternal thyroid hormone production. (7)(9) In fact, T4 production increases by about 50% during pregnancy. In early pregnancy, a fetus’s thyroid is not yet fully developed, meaning it relies on maternal thyroid hormones. (9)
Severe iodine deficiency in pregnant individuals can cause neurodevelopmental deficits and may contribute to growth delays in the fetus. In some cases, iodine deficiency may also lead to miscarriage and stillbirth. Furthermore, chronic (long-term) cases of severe iodine deficiency may lead to a condition known as cretinism, which is characterized by stunted growth and intellectual disability among many other abnormalities. (9)
To support the increased demand on the thyroid and to ensure optimal iodine status during pregnancy, the American Thyroid Association recommends that individuals who are planning to become pregnant and those who are currently pregnant or lactating supplement their diet with potassium iodide, a common form of iodine. The American Academy of Pediatrics also recommends that these individuals supplement with at least 150 mcg of iodine and consume iodized salt. Iodine supplementation may not be right for you, and taking iodine unnecessarily can cause adverse health effects. (9)
Talk to your practitioner to determine if you need iodine supplementation to support your thyroid before, during, and after pregnancy.
3. Breast health
Iodine deficiency is associated with an increased risk of fibrocystic breast disease, a condition characterized by non-cancerous lumps in the breast. (10) Research examining the effects of iodine supplementation in individuals with fibrocystic breast disease found that iodine supplementation reduced breast pain and tenderness. In one review, 65% of individuals taking iodine reported a reduction in pain versus 33% of women receiving a placebo. (3) Another study demonstrated a significant improvement in breast pain and tenderness following three months of iodine supplementation. (6)
Some research suggests that adequate iodine consumption may be protective against breast cancer. Certain populations around the world that consume plenty of iodine-rich foods report lower incidences of breast cancer. Interestingly, Japanese women living in Japan have significantly lower breast cancer incidences compared to women living in western countries. (10) Sea vegetables are naturally rich in iodine and are a popular dietary staple among people living in Japan. Some of the most popular sea vegetable products include kelp (8,000 mcg/g), kombu (2,353 mcg/g), wakame (42 mcg/g), and nori (16 mcg/g). (13)
Did you know? Breast tissue contains the highest concentration of iodine in the body. (9)
4. Radiation exposure
Potassium iodide (KI) is the same form of iodine commonly used in supplements and iodized salt. KI has been shown to temporarily protect the thyroid from the damaging effects of radioactive iodine. The Centers for Disease Control and Prevention (CDC) recommends that individuals take potassium iodide only when directed by public health or emergency management officials following a radiation emergency. Taking KI unnecessarily or taking large doses can pose serious health risks. (2)
Iodine deficiency affects approximately 38% of people worldwide. (8) When left unaddressed, iodine deficiency can affect thyroid functioning and fetal growth and development. (9) Certain populations are at increased risk of iodine deficiency or inadequacy. Risk factors include:
- Adoption of a vegan or vegetarian diet
- Food allergies to dairy, fish, or shellfish
- Lactose intolerance
Signs and symptoms of iodine deficiency include:
- Goiter (enlargement of the thyroid gland)
- High levels of thyroid-stimulating hormone (TSH)
- Hypothyroidism (underactive thyroid gland)
- Impaired mental function
- Pregnancy complications (e.g., miscarriage, stillbirth, pre-term birth, congenital abnormalities) (1)(5)
Most iodine supplements are available in one of two forms: potassium iodide or sodium iodide. Although the body requires iodine for many functions, consuming too much iodine can pose some health risks. In fact, excess iodine can cause similar symptoms to iodine deficiency, including high TSH levels, goiter, and hypothyroidism. If your practitioner suspects that you may be iodine deficient, they can order a simple urine test to confirm. Only supplement with iodine when explicitly instructed to do so by your practitioner. (9)
The bottom line
Iodine is an essential trace mineral found in various foods such as dairy, seaweed, fish, and iodized salt. Consuming enough, but not too much, iodine helps maintain normal thyroid function, promote healthy breast tissue, and encourage proper fetal growth and development. Iodine in the form of potassium iodide can even be used in emergency situations involving radiation exposure.
Iodine deficiency is rare in North America; however, specific populations may be more at risk. To avoid disrupting the delicate balance of thyroid hormones, always speak to a practitioner before supplementing with iodine.
- American Thyroid Association. (2021). Iodine deficiency. https://www.thyroid.org/iodine-deficiency/
- Centers for Disease Control and Prevention. (2020). Facts about potassium iodide. https://www.cdc.gov/nceh/radiation/emergencies/ki.htm#
- Ghent WR, Eskin BA, Low DA, Hill LP. Iodine replacement in fibrocystic disease of the breast. Can J Surg. 1993 Oct;36(5):453-60. PMID: 8221402.
- InformedHealth.org . Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. How does the thyroid gland work? 2010 Nov 17 .
- Kapil U. (2007). Health consequences of iodine deficiency. Sultan Qaboos University medical journal, 7(3), 267–272.
- Kessler, J. H. (2004). The effect of supraphysiologic levels of iodine on patients with cyclic mastalgia. The Breast Journal, 10(4), 328–336.
- Lee, S. Y., & Pearce, E. N. (2015). Iodine intake in pregnancy—even a little excess is too much. Nature Reviews Endocrinology, 11(5), 260–261.
- Leung, A., Pearce, E. N., & Braverman, L. E. (2010). Role of iodine in thyroid physiology. Expert Review of Endocrinology & Metabolism, 5(4), 593–602.
- Office of Dietary Supplements. (2022). Iodine. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
- Rappaport, J. (2017). Changes in dietary iodine explains increasing incidence of breast cancer with distant involvement in young women. Journal of Cancer, 8(2), 174–177.
- Roti, E., & Uberti, E. D. (2001). Iodine excess and hyperthyroidism. Thyroid, 11(5), 493–500.
- Ruggeri, R. M., & Trimarchi, F. (2021). Iodine nutrition optimization: Are there risks for thyroid autoimmunity? Journal of Endocrinological Investigation, 44(9), 1827–1835.
- Zava, T. T., & Zava, D. T. (2011). Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis. Thyroid Research, 4(1), 14.