Iodine is an essential trace mineral not made by the body so must be obtained by food or supplements. It is found naturally in some foods and is added to supplements and some salt seasonings. Iodine is needed to make the thyroid hormones thyroxine and triiodothyronine, which assist with the creation of proteins and enzyme activity, as well as regulating normal metabolism. Without enough iodine, these thyroid hormones do not work properly and can lead to an under-active or overactive thyroid gland, causing the medical conditions of hypothyroidism and hyperthyroidism with various negative side effects in the body.
Iodine is a micronutrient necessary for human development and health. It is required for the synthesis of thyroxine (T4) and triiodothyronine (T3), two thyroid hormones that play key roles in human metabolic functions and processes. It is derived mainly from diet, and is dependent on concentrations in soil and water as well as supplementation. Excess iodine is primarily eliminated in urine.
Until about 100 years ago, lack of dietary iodine played a major role in the prevalence of goiter (enlarged and malfunctioning thyroid gland) and certain types of neurocognitive impairment. These conditions are today rarely seen in the developed world, but are still evident in certain areas of China, India, Central Asia, and Central Africa.
Iodine’s role in curing and preventing thyroid disease has long been recognized, but it was not until the early 20th century that public health steps began to be taken to ensure improved population access. Iodized salt and iodine tablets were first introduced into Canada, Switzerland, and the U.S. shortly after the First World War (early 1920s).
In 1990, the United Nations World Summit for Children set forth the goal of eliminating iodine deficiency worldwide, resulting in the issuance in 1993 of recommended standards for universal salt iodization by the World Health Organization (WHO) and the United Nations International Children’s Emergency Fund (UNICEF). The standard recommended that “All food- grade salt, used in household and food processing, should be fortified with iodine as a safe and effective strategy for the prevention and control of iodine deficiency disorders in populations living in stable and emergency settings.”
Today, universal salt iodization (USI) has been implemented in more than 120 countries,2 and approximately 86% of the world’s population currently has at least some access to iodized salt.
The benefits of correcting iodine deficiency are remarkable: Goiter, if caused by an iodine deficiency, is directly treatable using iodine. In addition, some systematic reviews have shown that providing iodized salt to populations has brought both a significant reduction in the risk of low intelligence (defined as IQ <70), and an almost 10-point overall increase in population IQ among iodine-deficient children.3, 4
Unfortunately, however, iodine deficiency disorder is still a major global public health problem today. As of 2012, an estimated 2.2 billion people worldwide were known to be living in iodine-deficient areas.
Recommended Amounts
RDA: The Recommended Dietary Allowance for iodine is 150 micrograms (mcg) daily for adult men and women 19+ years, and 220 and 290 mcg daily for pregnant and lactating women, respectively. [1,2]
UL: A Tolerable Upper Intake Level (UL) is the maximum daily dose unlikely to cause adverse side effects in the general population. The UL for iodine for adults 19+ years and pregnant and lactating women is 1,100 mcg daily.
Iodine is an element that plays an essential role in the functioning of a healthy thyroid. It is used for the production of thyroid hormones. It is particularly important in women who are pregnant as it is needed to ensure the development of a baby’s brain during pregnancy and early life.
Adults need 150mcg of iodine per day.
Iodine and hypothyroidism
If you have hypothyroidism (underactive thyroid) and are taking levothyroxine you do not have a functioning thyroid to absorb iodine and therefore you do not require iodine supplements.
Iodine and hyperthyroidism
If you are being treated for hyperthyroidism (overactive thyroid), taking an iodine supplement is unnecessary and can worsen the condition.
However, unless instructed by your doctor to follow a low iodine diet, thyroid patients can have iodine-containing foods (milk, eggs, cheese, fish etc) within the recommended daily as part of a balanced diet.
Iodine and Health
Food Sources
Iodine is found in soil and the ocean, which varies in amount and will affect how much of the mineral is contained in a food. Iodine is found mainly in animal protein foods and sea vegetables, and to a lesser extent in fortified foods like breads, cereals, and milk.
- Seaweed (nori, kelp, kombu, wakame)
- Fish, shellfish (cod, canned tuna, oysters, shrimp)
- Table salts labeled “iodized”
- Dairy (milk, cheese, yogurt)
- Eggs
- Beef liver
- Chicken
- Fortified infant formula
Signs of Deficiency and Toxicity
Deficiency
Iodine regulates metabolism, the conversion of energy obtained from food into energy to help cells function and grow. A deficiency of iodine can therefore prevent normal growth and development. This is especially dangerous in pregnant women and infants, in which miscarriage, stillbirth, stunted growth, and cognitive impairments (difficulties with reading, writing, talking, problem solving, social skills) can occur. In adults, an iodine deficiency of less than 10-20 mcg a day can lead to inadequate thyroid hormone production, called hypothyroidism, which disrupts normal metabolic functions like regulating heart rate, body temperature, and body weight. [2] A lump or swelling in the neck, called goiter, often accompanies hypothyroidism. Other signs of hypothyroidism include:
- Fatigue, lethargy
- Weakness
- Sensitivity to cold
- Constipation
- Dry skin and hair
- Weight gain
People at risk for iodine deficiency include those who do not use iodized salt or supplements containing iodine, pregnant women, vegans who do not eat any animal foods, and those living in areas with low levels of iodine in the soil (e.g., mountainous regions).
Toxicity
High iodine intakes are usually well-tolerated in most healthy people and do not cause problems. [1] This has been observed in countries such as Japan and Korea that eat iodine-rich seaweed regularly. [3] But some people with autoimmune thyroid disease or who have a history of chronic iodine deficiency can be sensitive to receiving extra iodine, inducing conditions of iodine deficiency like hypothyroidism and goiter. [2,4] Excess iodine can also lead to too much thyroid hormone production, causing hyperthyroidism; signs of this condition are an increased metabolism that promotes weight loss, fast or irregular heartbeat, hand tremors, irritability, fatigue, and sweatiness. Sometimes even just a slight increase in dietary iodine above the RDA can cause iodine-induced hyperthyroidism in sensitive individuals. [4]
Some epidemiologic studies have shown that high seaweed intakes are associated with an increased risk of certain types of thyroid cancer, particularly in postmenopausal women, but the exact mechanism is unclear. [2,3]
Excess iodine intake may come from use of high-dose supplements or overeating certain seaweeds and salts that contain iodine. Severe iodine poisoning is rare, but symptoms include fever; stomach pain; nausea; vomiting; a burning sensation of the mouth, throat, and stomach; and even coma. [2] Children, infants, the elderly, and those with existing thyroid disease are particularly vulnerable to iodine toxicity and iodine-induced hypothyroidism and hyperthyroidism. [3,4]
What are the signs and symptoms of iodine deficiency?
You can identify an iodine deficiency by the effects it has on your thyroid.
One of the first signs of iodine deficiency is the enlargement of your thyroid. This is a condition called goiter. Your thyroid slowly grows larger as it tries to keep up with your body’s demand for more thyroid hormone. If you have a goiter, you may experience symptoms such as:
- Choking.
- Difficulty swallowing.
- Trouble breathing.
The main symptom of iodine deficiency is hypothyroidism. Hypothyroidism occurs when your body’s iodine level decreases and your thyroid gland can’t produce thyroid hormone. This condition is also called underactive thyroid. It causes your metabolism to slow down, leading to fatigue, weight gain and the inability to tolerate cold.
Other symptoms of iodine deficiency include:
- Infertility.
- Puffy skin.
- Hoarseness.
- Confusion.
- Scaly, dry skin.
- Coarse, thinning hair.
What causes iodine deficiency?
Iodine deficiency occurs when you don’t get enough iodine in your diet. While rare in the United States, iodine deficiency is a common condition in developing countries worldwide. People in areas far from water or at higher altitudes don’t get enough iodine through seafood or dairy. In addition, iodine isn’t added to table salt in some areas of the world.
Diagnosis and Tests
How is iodine deficiency diagnosed?
Your healthcare provider may be able to visually diagnose iodine deficiency if you have an enlarged thyroid gland or goiter. They may order imaging tests, such as a thyroid ultrasound or a thyroid scan to measure your thyroid gland and examine it for abnormalities.
Your healthcare provider may also order a thyroid blood test. Low levels of thyroid hormone or high levels of thyroid-stimulating hormone (TSH) can indicate iodine deficiency.
All newborn babies are checked for hypothyroidism through a blood test.
Management and Treatment
How is iodine deficiency treated?
Your healthcare provider will treat your iodine deficiency with iodine supplements. They may also recommend thyroid hormone supplements.
If your baby was born with iodine deficiency, the condition may be treated with thyroid hormone supplements. Depending on the severity of their condition, they may have to take thyroid hormones throughout their life.
Outlook / Prognosis
What can I expect if I have an iodine deficiency?
If you increase your iodine intake either through food or a supplement, the effects of iodine deficiency may decrease. If iodine deficiency isn’t caught early, severe effects can occur. If you’re pregnant, iodine deficiency can cause permanent birth defects. It’s important to get enough iodine through food or a supplement to prevent the effects from getting worse.
Prevention
How can I prevent iodine deficiency?
The best way to prevent iodine deficiency is to eat a diet that includes foods that contain iodine. Iodine can be found in:
- Certain fish, such as cod and tuna.
- Shrimp, seaweed and other seafood.
- Dairy products, such as milk, yogurt and cheese.
Using iodized salt is also an important way to prevent iodine deficiency. When you add salt to your food during cooking or eating, you should use iodized salt.
Most Americans get their salt intake from processed foods such as canned goods, but processed foods rarely contain iodized salt. These foods are usually made with non-iodized salt, so they don’t help with your iodine intake.
Other salts, including sea salt, kosher salt, Himalayan salt and fleur de sel, don’t contain iodine either.
The amount of iodine you need every day depends on your age. Most adults should get 150 micrograms of iodine daily. If you’re pregnant or breastfeeding, you should take a prenatal vitamin that contains 250 micrograms of iodine daily. Not all prenatal vitamins contain iodine, so double-check the nutrients on the bottle. Ask your healthcare provider if you should take a separate iodine supplement.
Did You Know?
- In the U.S., people obtain most of their dietary iodine from iodized salt and milk.
- Iodine supplements can interact with certain blood pressure medications and diuretics, including lisinopril, spironolactone, and amiloride, causing a dangerous buildup of potassium in the blood called hyperkalemia.
- Iodine is an ingredient in contrast agents that a person may take before having an X-ray or computed tomography (CT scan). It helps to absorb the rays so that clearer pictures of the body’s organs can be seen.
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