Why do hilly people suffer from simple goitre?

Simple goiter is a disease caused due to deficiency in iodine. We get iodine from salts. In coastal areas the salt content of soil is very high. Thus all the crops, vegetables, fruits, fish etc are rich in iodine. But as the hilly areas are far away from the sea coast, the iodine content of the hill soil is negligible. So people staying in hilly areas do not get adequate iodine through their diet. That is why they mostly suffer from simple goiter. They are prescribed to increase the intake of table salt to get rid of the iodine deficiency.