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Can You Eat Too Much Kelp?

By Victoria Weinblatt

Eating too much kelp can cause thyroid problems and increase your risk of arsenic poisoning. Naturally occurring iodine levels in kelp, a large brown algae, affect the amount of hormones your thyroid gland produces. Kelp that grows in water containing arsenic absorbs this toxic metal, and it passes into your body when you eat it. Kelp is frequently used in South Korean and Japanese food, and also sold as a dietary supplement. Avoid adverse reactions and consult your physician before adding kelp supplements to your diet.

Arsenic Levels

Eating too much kelp can cause arsenic poisoning, according to a report from the University of California at Davis reported in the April 2007 issue of the journal “Environmental Health Perspectives.” Researchers analyzed nine over-the-counter kelp supplements and found detectable levels of arsenic in eight of the products. Seven of those products exceeded the FDA’s tolerance level for arsenic in food products. None of the products featured arsenic toxicity warnings on the labels.

Arsenic Case Study

A 54-year-old woman took a kelp supplement regularly for several months and developed arsenic toxicity, according to a 2007 report from the UC Davis Occupational Medicine Clinic. The report reveals marine plants and seafood represent the highest dietary source of arsenic, a naturally occurring metal and a byproduct of industrial activities, for consumers. The woman’s symptoms, including impaired memory, vomiting and a rash, were so severe she had to leave her job. Blood and urine tests revealed arsenic in her urine. She stopped taking the kelp supplements and within several weeks her symptoms disappeared.


If you eat too much kelp, you may develop health problems because kelp is rich in iodine. The FDA’s recommended dietary intake of iodine is 150 mcg per day. The iodine content in kelp varies widely among supplements, which may cause you to take more than you need. According to information from the Langone Medical Center, the iodine content in kelp supplements ranges from 45 to 57,000 mcg per capsule.


Eating too much kelp may cause either an underactive or overactive thyroid from the iodine content, according to information from the Langone Medical Center. An underactive thyroid, called hypothyroidism, produces an insufficient amount of hormones; an overactive thyroid, called hyperthyroidism, produces too many hormones. People with a healthy thyroid gland should avoid high doses of kelp except under a doctor’s supervision.

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