Summarize this article:

Iodine deficiency used to be the major cause of goiters worldwide, but is now less common in parts of the world where iodine is added to packaged table salt (iodized salt). However, if you don’t regularly consume iodized salt, your doctor may ask you to increase your intake to about ½ teaspoon (4.8 g) of salt per day (enough to get 150 micrograms of iodine).  If you are on a very low-sodium diet, primarily use sea salt, or buy non-iodized table salt, it’s possible you might have an iodine deficiency. In some cases—for instance, if your body has difficulty processing iodine so it reaches your thyroid gland—your doctor may prescribe a daily iodine supplement. If you’re on a low-sodium diet for medical reasons and aren’t looking to increase your salt intake, you can ingest more iodine in other ways as well. Seawater is a natural source of iodine, so seaweed (kelp) and shellfish (shrimp in particular) are good food sources of iodine.  Sushi is a great source of seaweed/kelp. Seaweed and seaweed-derived iodine are also available in supplement form. You might, for instance, try eating shellfish 2-3 times per week and taking a daily kelp supplement for a few weeks, then go back to your doctor to check for improvement. If you live near the ocean, locally grown produce picks up iodine from the soil, and local dairy products will also contain higher amounts of iodine. In this case, “eating local” may benefit your thyroid and help reduce a goiter. If you live far from the sea, try eating more fruits and vegetables that are naturally higher in iodine, such as citrus, strawberries, lettuce, onions, and garlic. It may seem contradictory, but some goiters are caused by your thyroid getting too much iodine instead of too little. In this case, you need to cut back on iodized salt, shellfish, seaweed, and other higher-iodine foods. This is why it’s important to get a medical diagnosis instead of trying to treat a goiter on your own. Otherwise, you might increase your iodine intake and actually make the problem worse.

Summary:
Use iodized salt if you have an iodine deficiency. Increase low iodine by consuming seaweed and shellfish. Eat iodine-rich foods grown or raised in coastal areas, if possible. Reduce your iodine intake if advised by your doctor.