Iodine is a vital trace mineral that our bodies cannot produce on their own, making it essential to obtain it through our diet or supplements. Naturally present in certain foods and added to others like iodized salt, iodine plays a critical role in producing thyroid hormones, specifically thyroxine and triiodothyronine. These hormones are indispensable for protein creation, enzyme activity, and regulating metabolism. Insufficient iodine intake can hinder the proper functioning of these thyroid hormones, potentially leading to hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), both conditions associated with various adverse health effects.
Recommended Daily Intake of Iodine
Recommended Dietary Allowance (RDA): For adults aged 19 years and older, the recommended daily intake of iodine is 150 micrograms (mcg). This requirement increases to 220 mcg daily for pregnant women and 290 mcg daily for lactating women to support both maternal and infant health. [1,2]
Tolerable Upper Intake Level (UL): While iodine is essential, excessive intake can also be harmful. The Tolerable Upper Intake Level (UL) for iodine is set at 1,100 mcg per day for adults 19 years and older, including pregnant and lactating women. This level represents the maximum daily dose that is unlikely to cause adverse health effects in the general population.
The Importance of Iodine for Health
Iodine’s Role in Infant and Childhood Development: Iodine needs are heightened during pregnancy because thyroid hormone production increases significantly. Adequate iodine is crucial for the fetus and infant, supporting normal physical growth and brain development. Breast milk naturally contains iodine, with the concentration depending on the mother’s iodine intake. Many infant formulas are also fortified with iodine. However, it’s important to note that not all prenatal multivitamins contain iodine. The American Academy of Pediatrics recommends that pregnant and breastfeeding women ensure adequate iodine intake, often through iodized salt or supplements. [2] It’s worth noting that high-dose iodine supplements are not universally recommended and can potentially cause thyroid issues in some women.
Iodine deficiency, particularly moderate to severe deficiency in children, can have serious consequences, including lower IQ and stunted growth. Supplementation with iodine in deficient children has been shown to improve both physical and cognitive development.
Iodine, Hypothyroidism, and Hyperthyroidism: Hypothyroidism and hyperthyroidism are conditions resulting from the thyroid gland producing too little or too much thyroid hormone, respectively. An early indicator of hypothyroidism can be an elevated level of thyroid-stimulating hormone (TSH) in the blood. This can be triggered by insufficient iodine intake. Ironically, it can also occur in individuals with a history of iodine deficiency who suddenly consume high doses of iodine, such as through supplements. [1]
Goiter, characterized by a swelling in the front of the neck due to an enlarged thyroid gland, can be a symptom of hypothyroidism, hyperthyroidism, or even excessive iodine intake (typically from prolonged consumption of very high doses exceeding 18,000 mcg per day). [1] It’s also important to be aware of goitrogens, substances found in some cruciferous vegetables, which can interfere with iodine absorption, potentially affecting thyroid function and contributing to goiter, especially in individuals with existing iodine deficiency or hypothyroidism.
Top Food Sources of Iodine
The iodine content in food is influenced by the iodine levels in the soil and ocean where the food originates. Foods rich in iodine primarily include animal protein sources and sea vegetables, with smaller amounts found in fortified foods like bread, cereals, and milk. To increase your iodine intake, consider incorporating these foods high in iodine into your diet:
- Seaweed: Varieties like nori, kelp, kombu, and wakame are excellent sources of iodine.
- Fish and Shellfish: Aquatic foods such as cod, canned tuna, oysters, and shrimp are good sources of dietary iodine.
- Iodized Salt: Table salt labeled “iodized” is a readily available source of iodine.
- Dairy Products: Milk, cheese, and yogurt contribute to iodine intake.
- Eggs: Eggs are a decent source of iodine.
- Beef Liver and Chicken: These meats contain iodine, although in lesser amounts compared to seafood and dairy.
- Fortified Infant Formula: Infant formula is often fortified with iodine to meet the nutritional needs of babies.
Recognizing Iodine Deficiency and Toxicity
Iodine Deficiency Symptoms: Iodine is crucial for regulating metabolism, the process of converting food into energy for cell function and growth. Iodine deficiency can disrupt normal growth and development, posing significant risks, particularly for pregnant women and infants. In these vulnerable groups, deficiency can lead to miscarriage, stillbirth, stunted growth, and cognitive impairments (affecting reading, writing, communication, problem-solving, and social skills). In adults, iodine deficiency (less than 10-20 mcg daily) can result in inadequate thyroid hormone production, or hypothyroidism, disrupting vital metabolic functions such as heart rate regulation, body temperature control, and weight management. [2] Goiter, a swelling in the neck, is a common sign of hypothyroidism. Other symptoms of iodine deficiency and hypothyroidism include:
- Fatigue and lethargy
- Muscle weakness
- Increased sensitivity to cold temperatures
- Constipation
- Dry skin and hair
- Unexplained weight gain
Individuals at higher risk of iodine deficiency include those who do not use iodized salt or iodine-containing supplements, pregnant women, vegans who exclude all animal products from their diet, and people living in regions with iodine-poor soil, such as mountainous areas.
Iodine Toxicity Symptoms: In most healthy individuals, high iodine intakes are generally well-tolerated and do not cause adverse effects. [1] This is evident in populations like those in Japan and Korea, where regular consumption of iodine-rich seaweed is common. [3] However, certain individuals, particularly those with autoimmune thyroid disease or a history of chronic iodine deficiency, can be sensitive to increased iodine intake. In these cases, excess iodine can paradoxically trigger iodine deficiency conditions like hypothyroidism and goiter. [2,4] Excessive iodine can also lead to overproduction of thyroid hormone, resulting in hyperthyroidism. Symptoms of hyperthyroidism include an accelerated metabolism leading to weight loss, rapid or irregular heartbeat, tremors in the hands, irritability, fatigue, and excessive sweating. In sensitive individuals, even slight increases in dietary iodine above the RDA can induce iodine-induced hyperthyroidism. [4]
Some studies have suggested a link between very high seaweed consumption and an increased risk of certain types of thyroid cancer, especially in postmenopausal women, but the exact mechanisms are still being investigated. [2,3]
Iodine toxicity is more likely to arise from high-dose supplements or excessive consumption of certain seaweeds and salts that are heavily concentrated in iodine. Severe iodine poisoning is rare, but symptoms can include fever, abdominal pain, nausea, vomiting, a burning sensation in the mouth, throat, and stomach, and in extreme cases, coma. [2] Infants, children, the elderly, and individuals with pre-existing thyroid conditions are particularly vulnerable to iodine toxicity and iodine-induced thyroid disorders, including both hypothyroidism and hyperthyroidism. [3,4]
Interesting Facts About Iodine
- In the United States, the primary sources of dietary iodine are iodized salt and milk.
- Iodine supplements can interact negatively with certain blood pressure medications and diuretics, such as lisinopril, spironolactone, and amiloride, potentially leading to a dangerous buildup of potassium in the blood, a condition known as hyperkalemia.
- Iodine is a key component in contrast agents used in medical imaging procedures like X-rays and computed tomography (CT scans). These agents help improve image clarity by absorbing X-rays, allowing for clearer visualization of internal organs.
Related Resources
Vitamins and Minerals
References
Last reviewed March 2023
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