Over the past centuries large amounts of iodine have been leached from the surface soil by rain and carried back to the sea. Repeated flooding in areas which have had heavy rainfall also increases the depletion of iodine from the earth. Therefore, all crops grown in these areas lack iodine.
There is thus a prevalence of iodine deficiency diseases in third world countries. These diseases include goitre (enlargement of the thyroid gland!, miscarriages, stillbirths, loss of energy, reduced mental ability and retarded physical development. The Government directed that all salt manufactured after 1 December 1995, for sale in stores, must be iodated.