Iodine keeps your thyroid working and affects how your body uses energy

Iodine is a mineral your thyroid gland needs to make hormones that control your metabolism — how fast your body burns calories and produces heat. Without enough iodine, your thyroid can't do this job, and your metabolism slows down. This affects energy levels, body temperature, digestion, and even mood and concentration. Most people in the United States get enough iodine because it's added to table salt, but some groups — including pregnant women, people who avoid salt, and those eating mostly whole foods — may not get enough.

Your body doesn't make iodine, so it has to come from food or supplements. The amount you need is small — about 150 micrograms per day for adults — but that small amount is essential. When iodine intake drops too low over time, your thyroid enlarges (a condition called goiter) and thyroid function declines. During pregnancy and breastfeeding, iodine needs increase because the developing baby depends on the mother's thyroid hormones for brain and nervous system development.

Key Takeaways

  • Iodine is required for your thyroid to produce hormones that regulate metabolism, energy, and body temperature.
  • Most table salt in the U.S. contains iodine, so many people meet their needs without thinking about it, but not all salts do.
  • Pregnant and breastfeeding women need more iodine than other adults because thyroid hormones are critical for fetal brain development.
  • Seaweed, fish, eggs, and dairy products are natural food sources of iodine, though the amount varies depending on soil iodine content where the food was grown.

How iodine supports thyroid function and metabolism

Your thyroid produces two main hormones: T3 and T4. Both contain iodine atoms, and without iodine, your thyroid cannot assemble these molecules. When thyroid hormone levels drop, your metabolism slows — you may feel tired, gain weight more easily, feel cold, or notice your digestion slows down. This is why iodine deficiency is one of the most common preventable causes of thyroid problems worldwide.

The connection between iodine and energy is direct: thyroid hormones tell your cells how fast to burn fuel. Low iodine means lower thyroid hormone production, which means your cells receive a "slow down" signal. Over time, this can lead to hypothyroidism, a condition where the thyroid doesn't produce enough hormone. The symptoms are often subtle at first — fatigue, weight gain, dry skin, hair loss — but they worsen as deficiency deepens.

Iodine sources: salt, seafood, and other foods

Iodized salt is the most reliable source for most people. One-quarter teaspoon of iodized salt contains roughly 50 micrograms of iodine, so a typical diet with salt usually covers the daily need. However, not all salt is iodized — sea salt, kosher salt, and specialty salts often contain little or no iodine unless labeled otherwise. If you use non-iodized salt or avoid salt for health reasons, you'll need iodine from food or a supplement.

Natural food sources include seaweed (especially nori and kelp, which can contain very high amounts), fish and shellfish, eggs, and dairy products. The iodine content in these foods depends on the iodine level in the soil where animals grazed or where plants grew. Regions with iodine-poor soil produce lower-iodine foods, which is why iodine deficiency is still common in parts of Asia, Africa, and Eastern Europe despite being rare in the U.S. A single serving of seaweed can contain 100 to 8,000 micrograms of iodine — far more than the daily need — so seaweed should be eaten in moderation, not as a daily staple.

Who needs to pay closer attention to iodine intake

Pregnant and breastfeeding women are the highest-priority group. During pregnancy, the fetus relies entirely on the mother's thyroid hormones for brain development, especially in the first trimester. Iodine deficiency during pregnancy can impair fetal brain development and increase the risk of miscarriage and stillbirth. The recommended intake for pregnant women is 220 micrograms per day, compared to 150 for non-pregnant adults. Breastfeeding women need 290 micrograms daily because iodine passes into breast milk.

People who avoid salt, follow a vegan diet, or eat mostly whole foods prepared at home may also fall short. Vegans who don't eat dairy, eggs, or seafood and don't use iodized salt need to plan for iodine — either through seaweed (used sparingly), iodized salt, or a supplement. People with certain medical conditions, including some autoimmune thyroid diseases, may have altered iodine needs, so discussing iodine intake with a doctor is worthwhile if you have a thyroid diagnosis.

Iodine supplements: when and how to use them

Iodine supplements come in several forms: potassium iodide, sodium iodide, and kelp powder. Potassium iodide and sodium iodide are the most standardized — you know exactly how much iodine you're getting. Kelp and other seaweed supplements vary widely in iodine content and can deliver far more than you need in a single dose, which can cause problems. If you take a multivitamin, check the label: many contain 150 micrograms of iodine, which is the full daily amount.

The typical supplement dose for adults is 150 micrograms daily. Pregnant women often take prenatal vitamins that contain 220 to 290 micrograms. Taking more than 1,100 micrograms per day regularly can cause thyroid problems, so supplementing beyond what a prenatal vitamin or standard multivitamin provides should be discussed with a doctor first. If you're considering a kelp supplement, ask a healthcare provider about the iodine content and whether it's appropriate for your situation.

Signs you might not be getting enough iodine

Early signs of iodine deficiency include fatigue, weight gain, cold sensitivity, dry skin, hair loss, and difficulty concentrating. These symptoms overlap with many other conditions, so they're not a reliable way to diagnose deficiency on your own. A more specific sign is an enlarged thyroid (goiter), which you might notice as a swelling in the front of your neck, but this develops only after prolonged deficiency.

If you suspect you're not getting enough iodine — because you avoid salt, follow a vegan diet, or are pregnant — the most straightforward step is to talk with your doctor. They can order a thyroid function test or urine iodine test to measure your iodine status. This is especially important during pregnancy, when iodine deficiency can have lasting effects on fetal development.

Balancing iodine intake: too much is also a problem

While iodine deficiency is the main concern in most of the world, excessive iodine can also disrupt thyroid function. Taking very high doses of iodine supplements, eating large amounts of seaweed regularly, or using iodized salt heavily can push intake above safe levels. High iodine intake can trigger or worsen autoimmune thyroid disease in people who are genetically susceptible, and it can cause thyroid inflammation and dysfunction.

The safe upper limit for iodine is 1,100 micrograms per day for adults. This is rarely reached through food alone — even seaweed eaters would have to consume very large amounts daily. The risk is mainly from supplements or kelp products taken without medical guidance. If you're taking an iodine supplement, a multivitamin with iodine, and eating iodized salt, you could exceed safe levels, so checking labels and talking with a doctor about your total iodine intake makes sense.

Frequently Asked Questions

Do I need an iodine supplement if I use iodized salt?

Probably not. One-quarter teaspoon of iodized salt provides about 50 micrograms of iodine, and most people using iodized salt in cooking and eating processed foods (which often contain iodized salt) meet the 150-microgram daily target. If you avoid salt, use non-iodized salt, or follow a vegan diet without dairy or eggs, a supplement or iodized salt becomes more important.

Is seaweed a good everyday source of iodine?

Seaweed contains iodine, but the amount varies wildly — from 100 to 8,000 micrograms per serving depending on the type and where it was harvested. Eating seaweed occasionally is fine, but using it as a daily iodine source can easily push you over the safe upper limit. If you eat seaweed regularly, keep portions small and don't combine it with iodized salt and supplements.

What should pregnant women do about iodine?

Pregnant women should aim for 220 micrograms of iodine daily. Most prenatal vitamins contain this amount, so taking a prenatal vitamin covers the need. If you're pregnant and don't take a prenatal vitamin, or if you avoid salt and don't eat dairy or seafood, talk with your doctor about whether a separate iodine supplement makes sense for you.

Can iodine deficiency cause weight gain?

Yes. When iodine is low, thyroid hormone production drops, and your metabolism slows. This means your body burns fewer calories at rest, making weight gain easier. However, weight gain has many causes, so low iodine is just one possibility. If you've gained weight and suspect thyroid problems, a doctor can test your thyroid function and iodine status.

What's the difference between iodized salt and sea salt?

Iodized salt has iodine added during processing; sea salt is harvested from seawater and typically contains little iodine unless it's labeled as iodized. Both are salt, but only iodized salt reliably provides iodine. If you prefer sea salt or kosher salt, check the label — some brands now offer iodized versions, or you can use iodized table salt for cooking and specialty salts for finishing dishes.