Kelp and Iodine Overdose

A side of seaweed salad on a table at a Japanese restaurant.
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Kelp is a type of seaweed known for its rich iodine content. It is available as a dietary supplement in the form of capsules, powder and teas. It is commonly marketed for thyroid support. You should use caution when taking kelp supplements. Excess iodine from kelp can cause adverse health effects. Consult your doctor before taking kelp supplements.

Iodine Significance

Iodine is a trace mineral, and your body requires only a small amount. According to the University of Maryland Medical Center, the recommended dietary iodine intake for people over 10 years old is 120 to 150 mcg per day. Your thyroid contains about 70 to 80 percent of the iodine found in your body. Your muscles, ovaries and blood contain the rest. Your body produces no iodine, so it must come from your diet. Shellfish, kelp and deep water fish contain iodine. However, iodized salt is the primary source of iodine in your diet.


Iodine and Your Thyroid

Your thyroid is a small endocrine gland found in the front of your neck. It produces thyroid hormones from iodine and the amino acid tyrosine. Thyroid hormones control your metabolism. When your thyroid produces too little hormone, it is called hypothyroidism. When it produces too much hormone, it is known as hyperthyroidism, or thyrotoxicosis. Hypothyroid symptoms include fatigue, weight gain and constipation. Hyperthyroid symptoms include weight loss, hair loss, irritability and frequent bowel movements.

Excess Iodine from Kelp

Excess iodine from kelp or other dietary sources can adversely effect your thyroid. According to a case report published in the June 2006 issue of the "Journal of General Internal Medicine," a woman experienced iodine-induced thyrotoxicosis from consuming a kelp-containing tea. She consumed an estimated 580 to 990 mcg of iodine from the kelp tea daily for one month. Antithyroid medication helped bring her thyroid hormones into a normal range.


Iodine Intake and Kelp Safety

Since being added to salt, iodine deficiency is uncommon. Taking kelp specifically for its iodine content is considered unnecessary. Men in the United States between age 25 to 30 consume iodine at an estimated 410 mcg per day. Women between the same age consume about 260 mcg per day. The iodine level from kelp needed to cause overdose will vary from person to person depending on individual physiological factors. Your thyroid uses a complex system to deal with excess iodine. Consult your doctor before supplementing kelp.

Related Reading

Iodine is a trace element, meaning the body only needs it in small quantities. Humans require about 0.15 mg of iodine daily for oxygen transportation, energy processing and thyroid hormone production. Iodine deficiency in the United States is rare due to iodized salt; most iodine deficiencies occur in under-developed countries where iodine and iodized salt are expensive. A natural source of iodine is kelp, a sea vegetable that absorbs the mineral from ocean water. The discovery of kelp as a source of iodine in the 1700s, led to the treatment of goiter, or enlarged thyroid gland. Consult a qualified health care provider before taking kelp or iodine supplements.


Sources of Kelp

Dried and whole kelp can be found in many grocery stores, Asian markets and health-food stores. It is dried for use in supplements and available in tablet, capsule or powder form. Kelp is also marketed as spirulina or blue-green algae. The American Cancer Society recommends eating whole seaweed as opposed to taking supplements, since dried seaweed contains high amounts of nutrients that may be harmful.

Uses of Kelp

Kelp may have other uses aside from treating hypothyroidism. Japanese women have a lower incidence rate of breast cancer, and longer life expectancy after breast cancer, than American women. Higher seaweed consumption is one explanation for this phenomenon. The American Cancer Society reports that some forms of algae slow cancer growth in laboratory studies. In addition, high blood pressure treatment may include the use of seaweed, since it helps remove sodium from the bloodstream.


Iodine Toxicity

Just as a deficiency of iodine can disrupt production of thyroid hormones, too much iodine can block the production of hormones in the thyroid gland and also cause hypothyroidism. In Japan, where high amounts of seaweed are consumed, some people exhibit this type of blockage causing diet-induced goiter; this condition ceases when seaweed consumption is reduced. An excess of iodine can also lead to Grave's disease, thyroid cancer and toxic levels of thyroid hormones. The Food and Drug Administration recommends a maximum of 225 mcg of kelp per day. Symptoms of iodine poisoning include abdominal pain, diarrhea, fever, mouth tastes of metal, lack of urination, seizures, shortness of breath, thirst or vomiting. MedlinePlus recommends immediate medical treatment.


Read labels carefully. A UC Davis study released in April 2007 found that kelp naturally contains organic arsenic and may cause arsenic poisoning when exceeding the recommended amount. Researchers evaluated nine different kelp products and found that eight contained unacceptable levels. Iodine intake may also interact with other medications containing potassium iodide such as lithium or warfarin. Safety during pregnancy has not been established. Kelp use can cause skin to turn yellow, or look jaundiced, due to its high amount of carotenoids.