Iodine is needed by the thyroid gland to manufacture thyroid hormones. The iodine needed is normally obtained in food, but the soils in some parts of the world are deficient in iodine and the food does not contain enough iodine. Thyroid hormone production in people living in these areas is suppressed and they suffer Hypothyroid symptoms. The overstimulation of the thyroid gland by the pituitary in an attempt to make more hormone also commonly leads to an enlarged thyroid gland (which is referred to as a goitre).
The iodine deficient regions of the world are generally in elevated and alpine areas far from the sea. Many parts of SE Asia are iodine deficient as is Switzerland. In Australia the iodine deficient areas follow the Great Dividing Range including New England, Canberra, Gippsland and Tasmania. The 'Gippsland Goitre' was well known in years past. Iodine deficiency has been reduced in Australia through iodine supplementation an also through the use of iodine based disinfectants in the dairy industry (which led to increased iodine in milk). There is some recent evidence that iodine deficiency may be returning in Australia as the dairy industry reduces its reliance on iodine based disinfectants.
Iodine deficiency is a very serious problem for newborns and young children because thyroid hormones are essential for growth and the normal development of the brain. Inadequate dietary iodine leads to stunted growth and significant intellectual impairment - which is referred to as Cretinism.
The recommended treatment is iodine supplementation in the diet using iodised salt (the bottles with the green labels) or food rich in iodine. Seafoods, including seaweeds, are high in iodine and are a good source of extra iodine. But care should be exercised because iodine supplementation can be taken too far.
The daily requirement for iodine is very small at some 150 mcg (microgram or millionths of a gram). This means that a person needs about 1 teaspoon full over their whole life. Whilst the normal thyroid gland is tolerant of substantial excess iodine, a diseased or susceptible thyroid is not. Excess iodine can trigger thyroid disease and can make existing conditions worse. A person with a multinodular goitre or Graves’ disease in remission may be precipitated into hyperthyroidism whereas a person with impaired thyroid function may have worsening to hypothyroidism, or goitre growth from excess iodine exposure. A regular intake of the correct amount of iodine is recommended. Some supplements like kelp tablets can contain milligram amounts of iodine and deliver 100's of times the daily requirement so check what you use.
Iodine supplementation is not a substitute for thyroid hormone replacement for those with thyroid function problems or those whose thyroid has been removed.
