Iodine is an essential trace mineral that is present in a variety of seafood and dairy products. The thyroid gland --- an organ in the front of the neck --- takes up iodine from the blood and produces two hormones that are instrumental for energy metabolism and the normal growth and development of humans. It's normal to take iodine supplements for the treatment of medical conditions related to iodine deficiency, such as an underactive thyroid gland. However, iodine deficiency in the developed world is rare, and too much iodine can cause its own problems.
Excessive Intake
The recommended upper limit for iodine --- and its electrically charged companion, iodide, which is present in iodized table salt --- is 1,100 mcg, or 1.1 mg, per day in adults. Beyond this threshold, iodine can cause side effects in some individuals, such as nausea, stomach pain, headaches, diarrhea and a metallic taste in the mouth. High levels of iodine can also cause thyroid problems rather than treat them. For example, prolonged intake of more than 18,000 mcg, or 18 mg, per day increases the risk of a goiter, or the enlargement of the thyroid gland.
Supplementation
Iodine supplements should be safe in low doses. However, the amount of iodine can quickly escalate. Only a few tablets, depending on the supplement, can exceed the upper limit without even taking into account the iodine in your diet. Supplements made with kelp seaweed may have especially high levels of iodine. In 2010, the Australian Medical Association warned that products containing seaweed can have adverse effects on your health.
Sensitivity
At normal doses, iodine supplementation is likely safe for children and pregnant or breastfeeding women, but people with autoimmune thyroid disorders --- in which the immune cells attack the body's own thyroid tissue --- may want to avoid taking anything. If you are particularly sensitive to iodine, then you can experience bleeding, bruising, fever, joint pain, allergic reactions and swelling in the lips and face. Death is extremely rare, even at high doses, but not beyond the realm of possibility.
Interactions
Iodine supplements, because they interact with medications, require extreme caution. Avoid supplements if you are taking anti-thyroid drugs intended to calm an overactive thyroid gland; iodine can counteract their helpful effects. Other potentially problematic interactions include lithium, amiodarone, water pills and medications for high blood pressure. There are no known interactions with foods and other supplements.
References
- Mayo Clinic; Can Iodine Supplements Help Regulate Thyroid Function in a Person with Hypothyroidism?; Todd B. Nippoldt; April 2010
- Oregon State University Linus Pauling Institute; Iodine; Jane Higdon; June 2003
- Medline Plus; Iodine; April 2011
- ABC News; Doctors Warn on Seaweed's Iodine Danger; October 2010
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