Goitre is a sign of iodine deficiency. Seafood has a lot of iodine in it, so by eating seafood you are preventing goiter. Also, in the olden days, people that lived in land-locked areas were the only ones getting goiter. However, the people that lived in coastal areas, where they were able to eat seafood readily did not suffer from this condition. Therefore, iodine is now added to salt, so that people don't get goiter. If you notice, the salt that you use is most probably called "iodized salt"...this is why.