Iodine is an essential trace element not produced by the body and must therefore be obtained through food or supplements. It is found naturally in some foods and is added to supplements and some salty seasonings. Iodine is needed to make the thyroid hormones thyroxine and triiodothyronine, which help in the creation of proteins and enzymatic activity, as well as in the regulation of normal metabolism. Without enough iodine, these thyroid hormones do not work properly and can result in underactive or overactive thyroid gland causing hypothyroidism and hyperthyroidism medical condition with various negative side effects in the body.

Recommended amounts

RDA: The recommended dietary allowance for iodine is 150 micrograms (mcg) per day for adult men and women 19 years of age and older, and 220 and 290 mcg per day for pregnant and lactating women, respectively. [1,2]

UL: A tolerable upper intake level (AMT) is the maximum daily dose unlikely to cause unwanted side effects in the general population. The UL for iodine for adults 19 years of age and older and pregnant and lactating women is 1,100 mcg per day.

Iodine and health

Food sources

Iodine is found in soil and the ocean, the amount of which varies and will affect the amount of minerals in a food. Iodine is found primarily in animal protein foods and seafood, and to a lesser extent in fortified foods such as bread, cereals and milk.

Signs of deficiency and toxicity

Deficiency

Iodine regulates metabolism, the conversion of energy obtained from food into energy to help cells function and grow. Iodine deficiency can therefore prevent normal growth and development. This is especially dangerous in pregnant women and infants, in whom miscarriage, stillbirth, growth retardation and cognitive impairment (difficulty reading, writing, speaking, problem solving, social skills) can occur. In adults, an iodine deficiency of less than 10-20 mcg per day can lead to insufficient production of thyroid hormones, called hypothyroidism, which disrupts normal metabolic functions such as the regulation of heart rate, body temperature and body weight. [2] A lump or swelling in the neck, called a goiter, often accompanies hypothyroidism. Other signs of hypothyroidism include:

• Fatigue, lethargy
• Weakness
• Cold sensitivity
• 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 foods of animal origin and those who live in areas with low iodine content in the soil (eg mountainous regions).

Toxicity

High iodine intakes are generally well tolerated by most healthy people and do not cause problems. [1] This has been observed in countries like Japan and Korea which regularly consume seaweed rich in iodine. [3] But some people with autoimmune thyroid disease or who have a history of chronic iodine deficiency may be sensitive to supplemental iodine intake, causing iodine-deficient conditions like hypothyroidism and goiter. [2,4] Too much iodine can also lead to excess production of thyroid hormones, causing hyperthyroidism; Signs of this disease are increased metabolism which promotes weight loss, fast or irregular heartbeat, hand tremors, irritability, fatigue and sweating. Sometimes even a slight increase in dietary iodine above the RDA can cause iodine-induced hyperthyroidism in susceptible people. [4]

Some epidemiological studies have shown that high seaweed consumption is associated with an increased risk of certain types of thyroid cancer, especially in postmenopausal women, but the exact mechanism is not clear. [2,3]

Excessive iodine intake can result from the use of high dose supplements or from overconsumption of certain algae and salts containing iodine. Severe iodine poisoning is rare, but symptoms include fever; Stomach pain; nausea; vomiting; a burning sensation in the mouth, throat and stomach; and even a coma. [2] Children, infants, the elderly, and people with existing thyroid disease are particularly vulnerable to iodine toxicity and iodine-induced hypothyroidism and hyperthyroidism. [3,4]

Did you know?

• In the United States, people get most of their dietary iodine from salt and iodized 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 absorb the rays so that clearer images of the body’s organs can be seen.

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