The trace mineral iodine is well known for its crucial role in enabling the body's manufacture of vital thyroid hormones, but it is also important for the health of the immune system and for optimal brain function. It is widely believed by many authorities that iodine deficiency should never be seen in the affluent West, although this problem affects millions throughout the developed world.

Some nutritionists argue, however, that this conventional view is too optimistic, because the content of all minerals in foods is heavily dependent on the mineral content of the soil from which those foods are derived. The assumption must therefore be that the continuing de-mineralisation of farm soils has led to a reduction in the amount of dietary iodine commonly consumed.