Iodine is a trace element, meaning the human body requires it in very small quantities for proper functioning. It is an essential nutrient for overall health. Since the body cannot produce iodine, it must be obtained through diet to meet daily requirements.
Recommended Daily Amounts
The Recommended Dietary Allowance (RDA) for iodine varies across different life stages. For adult men and women, the RDA is 150 micrograms (µg) per day. This amount meets the nutritional requirements of nearly all healthy individuals.
Infants from birth to 6 months require 110 µg per day, increasing to 130 µg per day for infants aged 7 to 12 months. Children aged 1 to 8 years need 90 µg daily, while those aged 9 to 13 years require 120 µg per day. Pregnant individuals have a higher requirement of 220 µg per day, and lactating individuals need 290 µg per day to ensure adequate transfer to the infant via breast milk. These recommendations are established by organizations like the Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine.
Why Iodine is Essential
Iodine’s primary function is its role in the synthesis of thyroid hormones. The thyroid gland uses iodine to produce thyroxine (T4) and triiodothyronine (T3). These hormones are regulators of metabolism, influencing how the body uses energy.
Thyroid hormones are also important for growth, development, and the maintenance of bodily functions. They impact energy production, oxygen consumption in cells, and the maturation of tissues throughout the body. This includes their contribution to brain and bone development, especially during growth periods.
What Happens with Insufficient Iodine
Insufficient iodine intake can lead to various health problems, primarily affecting the thyroid gland. A common sign of deficiency is goiter, an enlargement of the thyroid gland as it works harder to capture iodine. Prolonged deficiency can result in hypothyroidism, where the thyroid gland is underactive and produces insufficient thyroid hormones.
Symptoms of hypothyroidism include fatigue, unexplained weight gain, increased sensitivity to cold, and cognitive impairment. For infants and children, severe iodine deficiency during developmental periods can have irreversible effects. This can lead to intellectual disability, a condition historically known as cretinism, due to impaired brain development.
Dietary Sources of Iodine
Iodine is found naturally in various foods, with some sources being rich. Seafood, including fish and shellfish, are excellent sources because marine animals concentrate iodine from seawater. Seaweed, such as kelp and nori, is notably high in iodine.
Dairy products, like milk and yogurt, along with eggs, also contribute to iodine intake. In many regions, iodized salt serves as a primary source of dietary iodine, as salt is widely consumed. The iodine content in plant-based foods, such as certain fruits and vegetables, can vary significantly depending on soil iodine levels.
What Happens with Too Much Iodine
While iodine is necessary, excessive intake can also pose health risks. Consuming high amounts of iodine, often from certain supplements, can paradoxically lead to thyroid dysfunction, including hyperthyroidism (overactive) and hypothyroidism (underactive). Excessive iodine can inhibit thyroid hormone production or cause inflammation of the thyroid gland, known as thyroiditis.
The Tolerable Upper Intake Level (UL) for iodine, the maximum daily intake unlikely to cause adverse effects, is 1,100 µg per day for adults. Infants, the elderly, pregnant and lactating women, and individuals with pre-existing thyroid conditions may be more susceptible to adverse effects from excessive iodine. Many iodine or kelp supplements can contain amounts far exceeding daily recommendations, requiring careful monitoring.