Iodine deficiency
One of the biggest geochemical diseases is iodine deficiency. Thirty percent of the world is at risk for it and insufficient intake is the most common cause of mental retardation and brain damage. The sea is a major source of iodine and those who are further from it are at a disadvantage. Another source of it is in soil; however, goitrogens such as humus and clay trap the iodine, making it hard for people to access it. Some cultures actually consume the earth's minerals by eating soil and clay; this is known as geophagy. It is most common in the tropics, especially among pregnant women. The Ottomac people of South America engage in this practice and none have suffered from any health problems related with mineral/ Iodine deficiency.