Kelp supplements are commonly marketed for their rich mineral content and are particularly rich in iodine -- a trace mineral that your body needs in small amounts to function properly. As with all such aids, consult your physician before taking kelp supplements; they have the potential to cause unwanted side effects. A few safety considerations exist in regard to excess iodine and heavy-metal toxicity.
There is a potential for someone taking kelp supplements to overload his body with too much iodine. The American Thyroid Association released a statement in June 2013 expressing concern regarding iodine supplements. The ATA advises the public that many kelp supplements contain many thousand times more iodine than the Tolerable Upper Limit, which it states is 1,100 micrograms per day. The UL refers to the proposed maximum amount you can take without experiencing side effects. What's more, the recommended daily allowance for iodine is 150 micrograms daily for non-pregnant adults, according to the ATA.
May Cause Hyperthyroidism
Your thyroid uses iodine to make thyroid hormones, which regulate metabolism, among other things. One side effect of too much iodine is hyperthyroidism, a condition involving your thyroid producing excess hormone. An article published in June 2006 in the "Journal of General Internal Medicine" describes a case report of kelp tea causing hyperthyroidism. After drinking kelp tea for four weeks, a 39-year-old woman experienced bothersome symptoms such as goiter -- an enlarged thyroid gland. Subsequent tests confirmed hyperthyroidism, and doctors ruled out all other possible causes.
Heavy Metal Toxicity
Just as there is a risk of mercury toxicity from certain types of fish, kelp supplements carry a risk of heavy-metal toxicity from daily use. After a woman suffered arsenic poisoning from taking kelp supplements, researchers tested several commercially available kelp products. They found that eight out of nine samples showed detectable levels of arsenic higher than the Food and Drug Administration tolerance level of 0.5 to 2 parts per million for certain food products. The report was published in the April 2007 issue of the journal "Environmental Health Perspectives."
Avoid taking kelp supplements if you have a thyroid disorder. It may worsen your condition. If you have skin problems, you should avoid kelp supplements, which may cause skin outbreaks resembling acne. According to the American Cancer Society, some seaweed supplements contain elevated levels of sodium. For this reason, avoid taking kelp if you have high blood pressure or heart failure.