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Iodine is an essential mineral that your body cannot make.

Your thyroid gland uses it to make thyroid hormones, which help control growth, repair damaged cells and support a healthy metabolism (1, 2).

Unfortunately, up to a third of people worldwide are at risk of an iodine deficiency (3).

Those at the highest risk include (4, 5, 6):

• Pregnant women.
• People who live in countries where there is very little iodine in the soil. This includes South Asia, Southeast Asia, New Zealand and European countries.
• People who don’t use iodized salt.
• People who follow a vegetarian or vegan diet.

On the other hand, iodine deficiencies are rare in the US, where there are sufficient levels of the mineral in the food supply (7).

An iodine deficiency can cause uncomfortable and even severe symptoms. They include swelling in the neck, pregnancy-related issues, weight gain and learning difficulties.

Its symptoms are very similar to those of hypothyroidism, or low thyroid hormones. Since iodine is used to make thyroid hormones, an iodine deficiency means your body can’t make enough of them, leading to hypothyroidism.

Here are 10 signs and symptoms of an iodine deficiency.

Swelling in the front of the neck is the most common symptom of an iodine deficiency.

This is called a goiter and occurs when the thyroid gland grows too big.

The thyroid gland is a small, butterfly-shaped gland in the front of your neck. It makes thyroid hormones upon receiving a signal from the thyroid-stimulating hormone (TSH) (8, 9).

When blood levels of TSH rise, the thyroid gland uses iodine to make thyroid hormones. However, when your body is low in iodine, it can’t make enough of them (9).

To compensate, the thyroid gland works harder to try to make more. This causes the cells to grow and multiply, eventually leading to a goiter.

Fortunately, most cases can be treated by increasing your iodine intake. However, if a goiter hasn’t been treated for many years, it might cause permanent thyroid damage.

Summary: Swelling in the front of the neck, or a goiter, is a common symptom of an iodine deficiency. It occurs when your thyroid gland is forced to make thyroid hormones when there is a low supply of iodine in the body.

Unexpected weight gain is another sign of an iodine deficiency.

It may occur if the body does not have enough iodine to make thyroid hormones.

This is because thyroid hormones help control the speed of your metabolism, which is the process by which your body converts food into energy and heat (10, 11).

When your thyroid hormone levels are low, your body burns fewer calories at rest. Unfortunately, this means more calories from the foods you eat are stored as fat (10, 11).

Adding more iodine to your diet may help reverse the effects of a slow metabolism, as it can help your body make more thyroid hormones.

Summary: Low iodine levels may slow your metabolism and encourage food to be stored as fat, rather than be burned as energy. This may lead to weight gain.

Fatigue and weakness are also common symptoms of an iodine deficiency.

In fact, some studies have found that nearly 80% of people with low thyroid hormone levels, which occur in cases of iodine deficiency, feel tired, sluggish and weak (12).

These symptoms occur because thyroid hormones help the body make energy.

When thyroid hormone levels are low, the body can’t make as much energy as it usually does. This may cause your energy levels to plummet and leave you feeling weak.

In fact, a study in 2,456 people found that fatigue and weakness were the most common symptoms among those with low or slightly low thyroid hormone levels (13).

Summary: Low iodine levels may leave you feeling tired, sluggish and weak. This is because your body needs the mineral to make energy.

Thyroid hormones help control the growth of hair follicles.

When your thyroid hormone levels are low, your hair follicles may stop regenerating. Over time, this may result in hair loss (14).

For this reason, people with an iodine deficiency may also suffer from hair loss (15).

One study in 700 people found that 30% of those with low thyroid hormone levels experienced hair loss (16).

However, other studies have found that low thyroid hormone levels only seem to cause hair loss in those with a family history of hair loss (14).

If you experience hair loss because of an iodine deficiency, getting enough of this mineral may help correct your thyroid hormone levels and stop hair loss.

Summary: An iodine deficiency may prevent hair follicles from regenerating. Fortunately, getting sufficient iodine can help correct hair loss that occurs due to an iodine deficiency.

Dry, flaky skin may affect many people with an iodine deficiency.

In fact, some studies have found that up to 77% of people with low thyroid hormone levels may experience dry, flaky skin (12).

Thyroid hormones, which are made of iodine, help your skin cells regenerate. When thyroid hormone levels are low, this regeneration doesn’t occur as often, possibly leading to dry, flaky skin (17).

Additionally, thyroid hormones help the body regulate sweat. People with lower thyroid hormone levels, such as those with an iodine deficiency, tend to sweat less than people with normal thyroid hormone levels (18, 19).

Given that sweat helps keep your skin moist and hydrated, a lack of sweat may be another reason why dry, flaky skin is a common symptom of iodine deficiency.

Summary: Dry, flaky skin may occur with an iodine deficiency, as the mineral helps your skin cells regenerate. It also helps your body sweat and hydrates your skin cells, so an iodine deficiency can cause you to sweat less.

Feeling cold is a common symptom of an iodine deficiency.

In fact, some studies have found that over 80% of people with low thyroid hormone levels may feel more sensitive to cold temperatures than usual (12).

Since iodine is used to make thyroid hormones, an iodine deficiency can cause your thyroid hormone levels to plummet.

Given that thyroid hormones help control the speed of your metabolism, low thyroid hormone levels may cause it to slow down. A slower metabolism generates less heat, which may cause you to feel colder than usual (20, 21).

Also, thyroid hormones help boost the activity of your brown fat, a type of fat that specializes in generating heat. This means that low thyroid hormone levels, which may be caused by an iodine deficiency, could prevent brown fat from doing its job (22, 23).

Summary: Iodine helps generate body heat, so low levels of it may leave you feeling colder than usual.

Your heart rate is a measure of how many times your heart beats per minute.It may be affected by your iodine levels. Too little of this mineral could cause your heart to beat slower than usual, while too much of it could cause your heart to beat faster than usual (24, 25).

A severe iodine deficiency may cause an abnormally slow heart rate. This could make you feel weak, fatigued, dizzy and possibly cause you to faint (26).

Summary: An iodine deficiency may slow your heart rate, which may leave you feeling weak, fatigued, dizzy and at risk of fainting.

An iodine deficiency may affect your ability to learn and remember (27, 28, 29).

A study including over 1,000 adults found that those with higher thyroid hormone levels performed better on learning and memory tests, compared to those with lower thyroid hormone levels (30).

Thyroid hormones help your brain grow and develop. That’s why an iodine deficiency, which is required to make thyroid hormones, can reduce brain development (31).

In fact, studies have found that the hippocampus, the part of the brain that controls long-term memory, appears to be smaller in people with low thyroid hormone levels (32).

Summary: An iodine deficiency at any age may cause you to struggle to learn and remember things. One possible reason for this might be an underdeveloped brain.

Pregnant women are at a high risk of iodine deficiency.

This is because they need to consume enough to meet their own daily needs, as well as the needs of their growing baby. The increased demand for iodine continues throughout lactation, as babies receive iodine through breast milk (33).

Not consuming enough iodine throughout pregnancy and lactation may cause side effects for both the mother and baby.

Mothers may experience symptoms of an underactive thyroid, such as a goiter, weakness, fatigue and feeling cold. Meanwhile, an iodine deficiency in infants may stunt physical growth and brain development (4).

Furthermore, a severe iodine deficiency may increase the risk of stillbirth (34).

Summary: Getting enough iodine is especially important for pregnant and breastfeeding women, as they have higher needs. An iodine deficiency may cause severe side effects, especially for the baby, such as stunted growth and brain development.

Heavy and irregular menstrual bleeding may occur as a result of an iodine deficiency (35).

Like most symptoms of iodine deficiency, this is also related to low levels of thyroid hormones, given that iodine is needed to make thyroid hormones.

In one study, 68% of women with low thyroid hormone levels experienced irregular menstrual cycles, compared to only 12% of healthy women (36).

Research also shows that women with low thyroid hormone levels experience more frequent menstrual cycles with heavy bleeding. This is because thyroid hormones disrupt the signals of hormones that are involved in the menstrual cycle (37, 38).

Summary: Some women with an iodine deficiency may experience heavy or irregular periods. This is because thyroid hormones, which are made of iodine, may interfere with hormones that are involved in regulating the menstrual cycle.

There are very few good sources of iodine in the diet. This is one reason why iodine deficiency is common worldwide.

The recommended daily intake (RDI) is 150 mcg per day. This amount should meet the needs of 97–98% of all healthy adults.

However, pregnant or breastfeeding women need more. Pregnant women need 220 mcg daily, while lactating women need 290 mcg daily (39).

The foods below are excellent sources of iodine (39):

• Seaweed, one whole sheet dried: 11–1,989% of the RDI
• Cod, 3 ounces (85 grams): 66% of the RDI
• Yogurt, plain, 1 cup: 50% of the RDI
• Iodized salt, 1/4 teaspoon (1.5 grams): 47% of the RDI
• Shrimp, 3 ounces (85 grams): 23% of the RDI
• Egg, 1 large: 16% of the RDI
• Tuna, canned, 3 ounces (85 grams): 11% of the RDI
• Dried prunes, 5 prunes: 9% of the RDI

Seaweed is usually a great source of iodine, but this depends on where it came from. Seaweed from some countries, such as Japan, are rich in iodine (40).

Smaller amounts of this mineral are also found in a variety of foods like fish, shellfish, beef, chicken, lima and pinto beans, milk and other dairy products.

The best way to get enough iodine is to add iodized salt to your meals. Half a teaspoon (3 grams) over the course of the day is enough to avoid a deficiency.

If you think you have an iodine deficiency, it’s best to consult your doctor. They will check for signs of swelling (a goiter) or take a urine sample to check your iodine levels (41).

Summary: Iodine is found in very few foods, which is one reason why deficiency is common. Most healthy adults need 150 mcg per day, but pregnant and lactating women need more to meet the needs of their growing babies.

Iodine deficiencies are very common, especially in Europe and Third World countries, where the soil and food supply have low iodine levels.

Your body uses iodine to make thyroid hormones. That’s why an iodine deficiency can cause hypothyroidism, a condition in which the body can’t make enough thyroid hormones.

Luckily, deficiency is easy to prevent. Adding a dash of iodized salt to your main meals should help you meet your requirements.

If you think you have an iodine deficiency, it’s best to talk to your doctor. They will check for visible signs of an iodine deficiency, like a goiter, or take a urine sample.