Key Points:
- Iodine is an essential mineral that helps your body make thyroid hormones, which regulate metabolism, energy use, and growth.
- Getting enough iodine is especially important during pregnancy and breastfeeding to support a baby’s brain and nervous system development.
- Most people in the U.S. get enough iodine, but deficiency can still occur — particularly in people who don’t use iodized salt or who avoid dairy, seafood, and eggs.
- Too little iodine can lead to thyroid problems such as goiter, fatigue, weight gain, and cold sensitivity.
- Too much iodine can also disrupt thyroid function, so supplements should only be used if recommended by a healthcare provider.
- Good food sources of iodine include iodized salt, seafood, dairy foods, eggs, and seaweed.
Depending on how old you are, you might remember using iodine to treat cuts and wounds. While iodine is still used today to help prevent infection and support healing, it also plays several essential roles inside the body — particularly in supporting thyroid health and metabolism.
Why iodine matters for thyroid health
What iodine is and what it does in the body
Iodine is a mineral that cells need to help convert food into energy. However, its primary role in the body is to help produce thyroid hormones — thyroxine (T4) and triiodothyronine (T3). These hormones regulate many of the body’s biochemical processes, including protein production and metabolism, and are essential for proper bone and brain development during pregnancy and infancy.
Thyroid hormone production is controlled in part by thyroid-stimulating hormone (TSH), a hormone released by the pituitary gland. TSH helps maintain healthy thyroid hormone levels by signaling the thyroid gland to take up iodine and produce and release T3 and T4. This feedback system helps keep thyroid function in balance.
When iodine intake is too low, TSH levels can remain elevated as the body attempts to stimulate more thyroid hormone production. Over time, this can cause the thyroid gland to enlarge, leading to a condition called goiter, which may appear as a visible lump at the front of the neck.
Iodine and cognitive development in children
Iodine plays a critical role in brain and nervous system development, particularly during pregnancy, infancy, and early childhood. A severe iodine deficiency during these periods can lead to lasting cognitive and developmental impairments.
Some research suggests that low iodine intake during pregnancy may be associated with attention and learning difficulties in children. However, evidence is mixed, and iodine deficiency has not been shown to directly cause attention deficit disorder (ADD) or attention-deficit/hyperactivity disorder (ADHD).
Because iodine needs increase during pregnancy and breastfeeding, many national and international health organizations recommend iodine supplementation during these life stages. In fact, the American Thyroid Association and the American Academy of Pediatrics advise that women who are pregnant, planning to become pregnant, or breastfeeding take a daily supplement containing 150 micrograms (mcg) of iodine, typically as part of a prenatal vitamin.
Fibrocystic breasts
Some research has explored the use of iodine supplements in women with fibrocystic breasts, a benign condition that can cause breast pain, tenderness, and lumpiness. Fibrocystic breast changes can occur in women of reproductive age as well as after menopause. While iodine may play a role in symptom management for some women, more research is needed to better understand its effectiveness and appropriate use.
Iodine and radiation-induced thyroid cancer
In certain emergency situations, iodine can be used as a thyroid-blocking agent to help reduce the risk of thyroid cancer. During a radiation emergency — such as a nuclear accident — radioactive iodine may be released into the environment. According to the Office of Dietary Supplements of the National Institutes of Health, taking stable iodine can help prevent the thyroid gland from absorbing radioactive iodine.
The U.S. Food and Drug Administration has approved potassium iodide for this use and offers age-based dosing guidance. Depending on age, exposed individuals may be advised to take between 16 and 130 milligrams (mg) of potassium iodide — but only when directed by public health officials during a radiation emergency.
Where it’s found
Iodine occurs naturally in some foods and is also added to salt labeled “iodized.” Because iodine is present in both soil and ocean water in varying amounts, the iodine content of foods can differ depending on where they are grown or produced.
One of the richest dietary sources of iodine is seaweed, including kelp, nori, kombu, and wakame, although iodine levels can vary widely among different types. Other reliable food sources of iodine include:
- Seafood such as cod, tuna, shrimp, oysters, and mussels
- Milk and other dairy foods
- Yogurt and cheese
- Eggs
- Iodized salt
Some grain products may contain iodine, depending on how they are prepared. For example, certain breads are made using iodate dough conditioners, and pasta can absorb iodine if cooked in water made with iodized salt.
Iodine is also available as a dietary supplement, most commonly in the form of potassium iodide or sodium iodide. Many multivitamin-mineral supplements contain iodine, and supplements made from kelp are also available. Because iodine content can vary widely in kelp-based products, supplements should be used with caution and only when recommended by a healthcare provider.
How much you need
The Recommended Dietary Allowance (RDA) for iodine is:
- Adult men (19 years and older): 150 micrograms (mcg)
- Adult women (19 years and older): 150 mcg
- Pregnant women: 220 mcg
- Breastfeeding women: 290 mcg
Signs of deficiency
According to the website EndocrineWeb, iodine deficiency in the United States was common before the 1920s, particularly in the Great Lakes, Appalachian, and Northwestern regions. The introduction of iodized table salt in the 1920s greatly reduced iodine deficiency nationwide.
Today, severe iodine deficiency is uncommon in the U.S., but certain groups remain at risk of not getting enough iodine. These include:
- People who do not use iodized salt
- Pregnant women, whose iodine needs are higher
- People who follow a vegan diet or who eat little or no dairy foods, seafood, and eggs
- People living in regions with iodine-deficient soil (more common outside the U.S.)
- People who consume very large amounts of goitrogens — substances in some foods that can interfere with iodine use, such as cabbage, broccoli, cauliflower, and Brussels sprouts. For most people in the U.S., these foods are not a concern when iodine intake is adequate.
Not getting enough iodine can lead to symptoms related to low thyroid hormone levels, including:
- “Brain fog,” or difficulty thinking clearly or concentrating
- Goiter (enlargement of the thyroid gland)
- Fatigue and weakness
- Sensitivity to cold
- Constipation
- Dry skin and hair
- Weight gain
- Joint pain
- Fertility problems
During pregnancy, iodine deficiency increases the risk of miscarriage, stillbirth, and preterm delivery. Babies who do not get enough iodine before birth or while nursing may experience long-term effects, including impaired growth, hearing and speech problems, and intellectual disabilities, according to EndocrineWeb.
Signs of toxicity
Getting too much iodine can disrupt normal thyroid function and, in some cases, cause symptoms similar to iodine deficiency, including goiter and hypothyroidism. Excess iodine may also trigger iodine-induced hyperthyroidism or thyroiditis, an inflammation of the thyroid gland. In rare cases, very high iodine intake has been associated with an increased risk of papillary thyroid cancer.
Acute iodine poisoning is uncommon and does not occur through food intake alone. When it does happen — typically due to excessive supplement use or medical exposure — symptoms may include:
- Burning of the mouth, throat, and stomach
- Fever
- Stomach pain
- Nausea, vomiting, and diarrhea
- Weak pulse
- Coma
The Tolerable Upper Intake Level (UL) for iodine is 1,100 micrograms (mcg) per day for adult men and women, including those who are pregnant or breastfeeding. According to the NIH Office of Dietary Supplements, “the ULs do not apply to individuals receiving iodine for medical treatment, but such individuals should be under the care of a physician.”
Other things to know about iodine
As more people limit their intake of salt, dairy foods, and bread, some health experts have raised concerns about a possible increase in iodine deficiency. According to the Academy of Nutrition and Dietetics, changes in eating patterns may make it harder for certain individuals to meet their iodine needs. Eating a varied diet that includes reliable sources of iodine can help reduce this risk. Women who are pregnant or breastfeeding may benefit from taking a prenatal vitamin that contains iodine.
It’s also important to be aware that iodine supplements can interact with certain medications, including:
- Anti-thyroid medications, such as methimazole (brand name Tapazole), used to treat hyperthyroidism
- ACE inhibitors, such as benazepril (Lotensin), lisinopril (Prinivil, Zestril), and fosinopril (Monopril)
- Potassium-sparing diuretics, such as spironolactone (Aldactone) and amiloride (Midamor)
Because too much iodine can interfere with thyroid function, it’s best not to take an iodine supplement unless directed by your healthcare provider.
The bottom line
Iodine is a vital nutrient for thyroid function and healthy growth and development, but more isn’t always better. Most people can meet their iodine needs through a balanced diet that includes iodized salt and iodine-rich foods. If you’re pregnant, breastfeeding, or considering an iodine supplement, talk with your healthcare provider to make sure you’re getting the right amount — safely.
Learn more about vitamins and minerals by reading the other pieces in this series:
What Calcium Does for Your Body — and How to Get Enough
Copper and Your Health: Benefits, Deficiency Signs, and Sources
The Facts About Fluoride: How Much You Need and Why It Matters
