Iodine is a trace mineral that the body needs to make thyroid hormones, which are essential for normal growth and development. In your body, about 70 – 80% of iodine is found in the thyroid gland in the neck. The rest is distributed throughout the body, particularly in the ovaries, muscles, and blood. If your body doesn’t have enough iodine, you can develop hypothyroidism (low thyroid hormone levels). Symptoms include sluggishness or fatigue, weight gain, dry skin, and sensitivity to temperature changes. Deficiency happens more often in women than in men, and is more common in pregnant women and older children. In infants and children, hypothyroidism can affect physical and mental development.
The classic sign of iodine deficiency is an enlarged thyroid gland. Some people with hypothyroidism develop an extremely large thyroid, known as goiter. Today, iodine deficiencies in the United States and other developed countries are rare because iodine is added to table salt. And crops in developed countries are generally grown in iodine rich soil, so there is more iodine in food. But in developing countries, where soil is often low in iodine, more than 1 billion people may be at risk for iodine deficiencies.
Iodine is also used to clean wounds, and iodine tablets can be used to purify water.
Most people get plenty of iodine, and because of the complex way iodine can affect the thyroid, you should not take iodine supplements unless your doctor tells you to.
Iodized salt is the main source of iodine in the diet. Plant and animal sea life, such as shellfish, white deep water fish, and brown seaweed kelp, absorb iodine from the water and are great sources of iodine. Garlic, lima beans, sesame seeds, soybeans, spinach, Swiss chard, summer squash, and turnip greens are also good sources of iodine. Bakeries may also add iodine to dough as a stabilizing agent, making bread another source of iodine.
The National Institute of Medicine Adequate Intake (AI) levels are as below:
- Infants ages 0 – 6 months: 2,200 mcg (micrograms) per day
- Infants ages 7 months – 1 year: 130 mcg per day
- Children ages 1 – 8 years: 90 mcg per day
- Children ages 9 – 13 years: 120 mcg per day
- Children ages 14 – 18 years: 150 mcg per day
- Ages 18 years and up: 150 mcg per day
- Pregnant females: 220 mcg per day
- Breastfeeding women: 290 mcg per day
The Tolerable Uptake Intake Levels (UL), which is the highest level of daily intake that’s not likely to result in side effects.
- Children 1 – 3 years: 200 mcg per day
- Children 4 – 8 years: 300 mcg per day
- Children 9 – 13 years: 600 mcg per day
- From 14 – 18 years (including pregnant and breastfeeding): 900 mcg day
- For adults older than 19 (including pregnant and breastfeeding): 1,100 mcg per day
Wounds or burns: Follow your health care provider’s instructions. Iodine is applied topically to the skin to prevent and treat infections from wounds and burns.
Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.
High doses of iodine may block the production of thyroid hormones, causing hypothyroidism (low thyroid hormone levels) in someone with otherwise normal thyroid function. Too much iodine can also increase the risk for other thyroid diseases, such as Hashimoto’s disease, Graves’ disease, certain thyroid cancers, and thyrotoxicosis (a dangerous condition involving a large amount of thyroid hormones in the bloodstream). For these reasons, you should not take iodine supplements without first talking to your doctor.
Taking more iodine per day than you usually get from table salt, or about 160 – 600 mcg (micrograms), may be harmful. Daily intake of 2,000 mcg iodine may be toxic, particularly in people with kidney disease or tuberculosis.
Routine thyroid function tests should be done on infants treated with topical iodine.
People with thryoid disease may be particularly susceptible to ill effects of iodine. People with dermatitis herpetiformis can have a worsening of symtoms when taking iodine.
Marina Muñoz Cervera