Iodine is a naturally occurring element and a required nutrient for human health. It is not produced by the body, so it must be obtained through food. This trace mineral plays an extensive role in various bodily functions. Its importance extends across all life stages, particularly during periods of rapid growth and development.
Iodine’s Role in Thyroid Health
The thyroid gland, a butterfly-shaped organ in the neck, relies on iodine to produce hormones. These hormones, primarily thyroxine (T4) and triiodothyronine (T3), form when iodine atoms attach to protein structures within the thyroid. T4 is the main hormone produced, with T4 making up about 80% of the thyroid’s output and T3 the remaining 20%.
In the bloodstream, T4 converts to the more active T3 in various tissues, including the liver and kidneys. Thyroid hormones regulate metabolism. They also influence heart rate, digestion, body temperature, muscle control, and brain development. The proper functioning of the thyroid gland, therefore, depends directly on a consistent and adequate supply of iodine.
Recognizing Iodine Imbalances
Both insufficient and excessive iodine intake can affect thyroid function. Low iodine levels lead to hypothyroidism (an underactive thyroid) as the body cannot produce enough thyroid hormones. Common symptoms include fatigue, weight gain, increased sensitivity to cold, dry skin, and constipation. A visible sign of deficiency is often a goiter (enlarged thyroid gland), as the gland attempts to capture more iodine.
Severe iodine deficiency during pregnancy can profoundly affect fetal and infant development, potentially causing stunted growth, intellectual disabilities, and problems with hearing and speech (sometimes called cretinism). Even mild deficiency in pregnant individuals can lead to subtle cognitive impairments in children.
Conversely, too much iodine can disrupt thyroid function, sometimes leading to hyperthyroidism (an overactive thyroid) or even hypothyroidism in susceptible individuals. Symptoms of hyperthyroidism include a rapid heart rate, weight loss despite increased appetite, increased sweating, and anxiety. Most healthy individuals tolerate higher iodine levels, but those with pre-existing thyroid conditions, infants, older adults, and pregnant individuals are more vulnerable to adverse effects from excess iodine.
Obtaining Sufficient Iodine
A balanced diet generally provides adequate iodine. Many foods naturally contain iodine or are fortified. Seafood (fish like cod and tuna, shellfish like shrimp and oysters, and seaweed) is rich in iodine from seawater absorption. For instance, a 3-ounce serving of baked cod provides about 158 micrograms of iodine, which meets the daily recommended intake for most adults.
Dairy products (milk, yogurt, cheese) also contribute, though concentration varies by cow’s diet and farm practices. Eggs are another source, with content influenced by chicken’s feed. Iodized salt is a widely available and effective source, as iodine is added during processing. Other plant-based foods (cereals, grains) contain some iodine, but levels depend on soil content. The recommended daily allowance for adults is 150 micrograms (mcg) per day.
Iodine Supplements and Considerations
Iodine supplements may be considered when dietary intake is insufficient. Pregnant and breastfeeding individuals have higher iodine requirements (approx. 220 mcg and 290 mcg daily, respectively) to support their health and fetal/infant development. For these groups, a daily supplement containing 150 micrograms of iodine is often recommended by health organizations. Vegans or those consuming limited dairy, seafood, and eggs may also need supplementation, as their dietary sources are restricted.
Despite benefits, approach iodine supplementation with caution. Excessive supplement intake can lead to thyroid dysfunction, including hyperthyroidism and hypothyroidism. The tolerable upper intake level for adults is 1,100 mcg per day; exceeding this can be harmful. Consult a healthcare professional before starting any iodine supplement, especially with pre-existing thyroid conditions, to determine appropriate dosage and avoid risks.