Why do we add iodine to our salt?

The main source of iodine is the sea and therefore seafood such as fish, shellfish and edible seaweed is an excellent source of iodine.  Iodine is also found in small amounts in our drinking water.  In areas where seafood is not available and where iodised salt is not used, the iodine intake is determined by the iodine content of the soil.  Iodine shortages are normally found in mountainous areas. 
 
A shortage of iodine in the diet can lead to goitres, or enlarged thyroid.  If the thyroid   enlarges too much, it can hamper breathing and swallowing.  A shortage of iodine can also lead to cretinism and retarded physical growth.  The most critical time a human being needs iodine is in the fetal stage and for young children.
 
The human body needs 120-140 micrograms of iodine per day.  Salt producers in South Africa are obliged by law to add 20-40 milligrams iodine per kilogram of salt.