Yes, you need iodine. It’s an essential mineral your body cannot make on its own, and without it, your thyroid gland can’t produce the hormones that regulate your metabolism, energy use, and body temperature. Most adults need 150 micrograms (mcg) per day, roughly the amount in a quarter teaspoon of iodized salt.
What Iodine Does in Your Body
Iodine has one primary job: it serves as the raw material for thyroid hormones. About 65% of the weight of T4, your thyroid’s main hormone, is iodine. When you eat iodine-containing food, your small intestine absorbs it and sends it into the bloodstream as iodide. Your thyroid gland then actively pulls that iodide from the blood and concentrates it at levels many times higher than the rest of your body.
Inside the thyroid, iodide gets oxidized and attached to a large protein. This chemical process produces two thyroid hormones: T4 (which contains four iodine atoms) and T3 (which contains three). These hormones travel through your blood and tell virtually every cell in your body how fast to burn energy. They help your body stay warm, keep your heart beating at the right pace, support brain function, and regulate how your organs work. Without enough iodine, this entire system slows down.
How Much You Need
The recommended daily intake for adults is 150 mcg. That number jumps significantly during pregnancy (220 mcg) and breastfeeding (290 mcg), because the developing baby depends entirely on the mother’s iodine supply to build its own thyroid hormones and develop a healthy brain and nervous system.
The safe upper limit for adults is 1,100 mcg per day. Going above that level can start to disrupt thyroid function, so more is not better. This upper limit applies equally to pregnant and breastfeeding women.
Best Food Sources of Iodine
Iodine content varies widely across foods, and some of the richest sources might surprise you. Based on USDA data, here’s what common foods provide per serving:
- Baked cod (3 oz): 146 mcg, nearly a full day’s worth
- Dried nori seaweed (2 tbsp, flaked): 116 mcg
- Whole milk (1 cup): 82 mcg
- Iodized table salt (1/4 tsp): 78 mcg
- Swiss cheese (1 oz slice): 41 mcg
- Cottage cheese (1/2 cup): 40 mcg
- Raw salmon (4 oz): 29 mcg
- One large egg: 25 mcg
- Canned tuna (3 oz): 8 mcg
Dairy is a surprisingly important source. Milk, cheese, and yogurt contribute a significant chunk of iodine intake for many people, particularly children. Fish varies dramatically: cod delivers nearly 20 times more iodine per serving than canned tuna. Iodized salt remains one of the most reliable and consistent sources, which is exactly why it was introduced in the first place.
Why Iodized Salt Exists
Before the 1920s, iodine deficiency was widespread in parts of the United States far from the ocean. The Great Lakes region, Appalachians, and Pacific Northwest were known as the “goiter belt,” where 26% to 70% of children had visibly enlarged thyroid glands. During World War I draft examinations in Michigan, over 30% of registrants had enlarged thyroids, and many were disqualified from military service because of it. The introduction of iodized table salt in the 1920s, modeled after a successful program in Switzerland, largely eliminated this problem within a generation.
What Happens When You Don’t Get Enough
The first sign of iodine deficiency is usually an enlarged thyroid gland, a condition called goiter. Your thyroid swells as it works harder to trap whatever small amount of iodine is available in the blood. Over time, insufficient iodine leads to hypothyroidism, where your body can’t produce enough thyroid hormone. That shows up as fatigue, weight gain, feeling cold, dry skin, and sluggish thinking.
The consequences are most severe during pregnancy. Iodine is essential for fetal brain and nervous system development. Depending on how severe the deficiency is and when it occurs during pregnancy, the effects can range from mild cognitive impairment to perinatal death. The most extreme outcome is congenital iodine deficiency syndrome, which causes intellectual disability, hearing loss, severe muscle stiffness, and short stature. Even mild deficiency during pregnancy carries risks. Some studies have found that pregnant women in the U.S. and parts of Europe still have iodine levels just below the adequate threshold.
Who Is Most at Risk for Deficiency
People who follow vegan diets face the highest risk in developed countries. Plant-based foods contain significantly less iodine than animal-derived ones, and vegan diets exclude nearly all the best sources: dairy, eggs, and fish. Plant-based milk alternatives like soy and almond beverages contain very little iodine unless they’ve been fortified. Studies consistently show that vegans have lower iodine levels than omnivores, whether measured through urine tests or estimated dietary intake.
Vegetarians fare somewhat better because they typically still consume dairy and eggs, but their levels still tend to fall below those of people who eat fish. Ironically, some vegans overcorrect by eating large amounts of seaweed or taking high-dose supplements, which can push them into iodine excess. If you follow a plant-based diet, iodized salt is your most practical and predictable source.
Pregnant and breastfeeding women are also at elevated risk simply because their needs are so much higher. A prenatal vitamin that contains iodine can help close the gap, though not all prenatal formulas include it.
Can You Get Too Much?
Yes. Your thyroid has a built-in safety mechanism: when iodine levels spike, the gland temporarily shuts down hormone production for a day or two, then adapts by reducing how much iodine it absorbs. This prevents a sudden flood of thyroid hormone. In healthy people, this system works well.
But in people with existing thyroid conditions, such as autoimmune thyroid disease or thyroid nodules, this regulation can fail. The result is either chronic hypothyroidism (too little hormone) or a surge of hyperthyroidism (too much). Excess iodine most commonly becomes a problem through high-dose supplements, very large amounts of seaweed, or medical procedures involving iodine-based contrast dye. It’s very difficult to get too much from ordinary food.
Staying below the 1,100 mcg upper limit is straightforward for most people eating a normal diet. The risk comes almost entirely from concentrated supplements or daily consumption of iodine-dense seaweed like kelp, which can contain thousands of micrograms per serving.
How Iodine Levels Are Measured
If you’re concerned about your iodine status, doctors can check it through a urine test. The World Health Organization considers a urinary iodine concentration between 100 and 199 mcg/L adequate for the general population. Below 100 indicates insufficient intake, with levels below 20 classified as severe deficiency. For pregnant women, the adequate range is higher: 150 to 249 mcg/L.
It’s worth noting that this test reflects recent iodine intake rather than long-term stores, so a single measurement can be influenced by what you ate in the past few days. It’s most useful as a population-level screening tool, but your doctor can interpret individual results alongside thyroid hormone levels to get a clearer picture.