"So iodine is crucial." More than 100 years ago, Americans were becoming deficient in the mineral iodine. It was causing problems like swelling ... but we do need some of it," says McCaffrey.

Insider's takeaway Iodine deficiency occurs when someone does not consume enough iodine-rich foods like seafood or iodized salt. Symptoms of an iodine deficiency include an enlarged thyroid ...

However, if you look ... of iodine, you don't need much of it per day to reach your recommended intake; only four teaspoons, and that's not considering other iodine-providing foods like fish ...