There’s no need to take iodine supplements—and you should especially avoid ones containing more than 500 micrograms, the American Thyroid Association has warned. That includes kelp (a type of seaweed) supplements. Though iodine is essential for normal thyroid functioning, the upper limit is 1,100 micrograms a day, and many supplements contain far more than that. The Recommended Dietary Allowance (RDA) for iodine is 150 micrograms a day for adults, which most people easily meet through their diets. Notable sources include iodized salt, seafood and dairy foods. There’s no need to get more than the RDA except under special circumstances, such as to treat severe hyperthyroidism or to protect the thyroid from radiation exposure.