How Much Iodine Per Day Does Your Thyroid Need?

Your thyroid needs about 150 micrograms of iodine per day to make the hormones that control your metabolism, heart rate, and body temperature. That is the Recommended Dietary Allowance for most adults, set by the National Academies. Pregnant women need 220 micrograms daily, and breastfeeding women need 290 micrograms. Your body cannot make iodine on its own, so it has to come from food, drinks, or supplements.

Most people in the United States get enough iodine without thinking about it. But some groups fall short, and the consequences range from a swollen thyroid to serious developmental problems in babies. Here is what the evidence actually shows about how much you need, who is at risk, and where iodine comes from.

How Much Iodine Per Day Does Your Thyroid Need?

The National Academies sets the Recommended Dietary Allowance at 150 micrograms per day for adults and children aged 14 and older. This is not a rough estimate. It is based on decades of research on thyroid hormone production and iodine balance.

Different life stages change the number. Here are the established values:

• Children ages 1 to 8: 90 micrograms per day
• Children ages 9 to 13: 120 micrograms per day
• Adults and teens 14 and older: 150 micrograms per day
• Pregnant women: 220 micrograms per day
• Breastfeeding women: 290 micrograms per day

The tolerable upper limit for adults is 1,100 micrograms per day. That is the highest daily intake unlikely to cause harm in most healthy people. Going above it occasionally is not dangerous for most adults, but consistently high intake can disrupt thyroid function.

Your thyroid gland is the only part of your body that actively concentrates iodine. It pulls iodine from your bloodstream and uses it to build two hormones: thyroxine (T4) and triiodothyronine (T3). Every cell in your body depends on these hormones to regulate how fast it uses energy. Without enough iodine, the whole system slows down.

What Happens When You Do Not Get Enough Iodine?

The thyroid responds to iodine shortage by working harder. It enlarges in an attempt to capture more iodine from the blood. This enlargement is called a goiter.

A goiter is the most visible sign of iodine deficiency. In mild cases, you may not notice it. In more serious cases, the thyroid becomes large enough to cause a visible swelling at the base of the neck, difficulty swallowing, or a feeling of pressure in the throat.

When iodine deficiency persists, the thyroid cannot produce enough hormones. This condition is called hypothyroidism. Symptoms develop slowly and include:

• Fatigue and weakness
• Weight gain despite normal eating
• Cold intolerance
• Dry skin and thinning hair
• Constipation
• Slowed thinking or memory problems
• Depression

In severe cases, iodine deficiency during pregnancy can cause intellectual disability and developmental delays in the baby. This is why the World Health Organization considers iodine deficiency the world’s most preventable cause of intellectual impairment. The damage to a developing brain from iodine deficiency is permanent and cannot be reversed after birth.

Iodine deficiency is rare in the United States today, largely because of iodized salt. But it has not disappeared. Some studies indicate that mild deficiency has become more common in certain populations, particularly among pregnant women and people who avoid salt or processed foods.

Which Foods Contain Iodine?

Iodine enters the food supply in several ways, and the amounts vary widely depending on where food is grown and how it is processed. This makes it hard to estimate your intake from food alone without checking labels.

Here are common sources with approximate iodine content:

Dairy products are a major iodine source in the American diet because iodine-based sanitizers are used on dairy equipment and because cattle feed is sometimes supplemented. This is why milk and yogurt contain more iodine than you might expect from the food itself.

Seaweed is unpredictable. Some types, like kelp, can contain thousands of micrograms of iodine in a single serving. Others, like nori, contain much less. Because the range is so wide, eating seaweed regularly can push you well above the upper limit without you realizing it.

Iodized salt is the most reliable source for most people. Not all salt is iodized, though. Sea salt, kosher salt, and specialty salts often contain little or no iodine. Check the label if iodine intake matters for you.

Who Is at Risk for Iodine Deficiency?

Pregnant and breastfeeding women have the highest risk. Their iodine needs are higher, and their bodies prioritize iodine for the baby. Even mild deficiency during pregnancy can affect the baby’s thyroid development.

People who follow certain diets may also fall short:

• Vegans and strict vegetarians — plant foods contain iodine only if the soil has it, and levels vary by region
• People who avoid salt — for medical reasons or by preference, this removes the most common iodine source in the US diet
• People with food allergies — avoiding dairy, eggs, and seafood eliminates several major iodine sources

People living in regions with iodine-poor soil are at risk worldwide, though this is less of a concern in countries with iodized salt programs. In the United States, iodized salt is voluntary, not mandatory, so intake depends on individual food choices.

Certain medical conditions also increase risk. People with thyroid disease, those who have had thyroid surgery, and those taking medications that affect thyroid function may need different amounts of iodine. These situations require guidance from a doctor, not a general guideline.

Can You Get Too Much Iodine?

Yes. The tolerable upper intake level for adults is 1,100 micrograms per day. Getting more than that consistently can cause problems, especially in people with existing thyroid conditions.

Excess iodine can trigger thyroid inflammation in some people. It can also cause either hypothyroidism or hyperthyroidism, depending on the individual and the amount. In people with autoimmune thyroid disease, even moderate increases in iodine intake can worsen the condition.

Some studies suggest that populations with very high iodine intake, such as in parts of Japan where seaweed is a dietary staple, have higher rates of certain thyroid disorders. The relationship is not simple, and researchers are still working out the details.

Supplements are a common source of excess iodine. Kelp supplements, in particular, can contain highly variable amounts. Some have been found to contain far more iodine than the label states. If you take a supplement, check the actual iodine content and stay within established limits unless a doctor tells you otherwise.

Do You Need an Iodine Supplement?

Most adults in the United States do not need an iodine supplement. The food supply provides enough for the general population, and taking extra iodine without a diagnosed deficiency offers no proven benefit.

Pregnant and breastfeeding women are the main exception. The American Thyroid Association recommends that women who are pregnant, breastfeeding, or planning pregnancy take a daily supplement containing 150 micrograms of iodine. This is in addition to iodine from food. The evidence for this recommendation is strong for populations with mild to moderate deficiency, which includes many parts of the United States.

If you are considering an iodine supplement for any other reason, talk to your doctor first. Iodine interacts with thyroid medications, and too much can be harmful if you have an underlying thyroid condition. There is no clinical evidence that iodine supplements improve energy, boost metabolism, or help with weight loss in people who are not deficient.

For most healthy adults, the simplest approach is to use iodized salt in cooking, include dairy or seafood in your diet if you eat them, and check with your doctor before adding a supplement.