Iodine (I2) is an essential trace element that is important to the function of the thyroid gland, and a crucial component of the thyroid hormone, thyroxine. Thyroxine is the hormone that regulates a persons basal metabolism, and without enough of this hormone the metabolism slows below what is considered normal. Weight gain, fatigue, and other health symptoms usually follow. Studies relating to Iodine were the first that demonstrated to scientists the importance of soil content in areas where food is grown. Through careful study, populations that were deficient in Iodine, and had higher rates of some cancers, indemic goiter, and cretenism, were found to be living in areas where the land had never been covered with ocean. This is significant because the ocean is our principal source of this important mineral. Aside from it’s role in basal metabolism, recent research has suggested that Iodine may be useful as an expectorant in cases of chronic obstructive pulmonary diseases.
Deficiencies
Iodine deficiency impairs growth and neurological development, which can damage the brain. Depending on its severity and stage of development at which it occurs, iodine deficiency can lead to a wide spectrum of health problems, ranging from mild intellectual impairment to severe mental retardation, growth stunting, apathy, and impaired movement, speech or hearing. Cretinism, in which many of these abnormalities occur, represents the extreme of early iodine deficiency. It is rare. Much more widespread is an intellectual blunting that may afflict as many as 50 million of the estimated 1.6 billion “at-risk” people living in iodine deficient regions, making iodine deficiency the most common preventable cause of mental retardation in the world. Because of decreased production of thyroid hormones, iodine deficiency causes compensatory hypertrophy of the thyroid gland as it attempts to make more thyroid hormone, resulting in a goiter – a disfiguring condition that is common in high risk areas. Collectively, health problems arising from a lack of iodine are known as iodine deficiency disorders (IDD).
Prevention and treatment: Universal salt iodization provides the most effective and affordable means to prevent IDD throughout the world; over 90 countries presently iodize their salt. Typically, the iodine concentration is from 30 to 100 µg per g of salt, levels that take into consideration anticipated losses during transport and storage. At salt intakes of 5-20 g per day, this fortification range is sufficient to meet requirements in most countries. Iodization costs between 2-7 US cents per kg of salt. Other iodizable vehicles include water, grain and dairy products. Iodized oil supplements may be periodically administered in remote areas where salt iodization is not feasible. Damage to the fetus resulting from maternal iodine deficiency is irreversible. Most goiters can be cured or reduced in size with iodine therapy.
Diet recommendations
The Recommended Dietary Allowance for iodine in the United States is as follows: infants, 40-50 µg; 1-3 yrs, 70 µg; 4-6 yrs, 90 µg; 7-10 yrs, 120 µg; over 11 yrs, 150 µg; pregnancy, 175 µg; and lactation, 200 µg. Globally, the per capita iodine requirement is 150-200 µg per day.
Food sources
Iodine content of food and water depends primarily on the supply of iodine in the soil. Glaciated, mountainous or heavy rainfall areas are likely to be low in iodine placing human and animal populations at risk. Thus, individuals can not usually improve iodine intake by diversifying their diet. Some plants, including cabbage, Brussels sprouts, legumes, and cassava contain goitrogenous substances that interfere with iodine absorption. This is of public health concern only where these foods are regularly consumed in large amounts and dietary iodine is low.
Toxicity
A wide range of iodine intake is tolerated by individuals. For this reason, long term consumption of iodine through iodized salt is considered safe. Chronic, excessive iodine intakes may occasionally lead to goiter and hypothyroidism. A small increase in thyrotoxicosis (<0.1%) may occur from increasing the iodine intake of a population which has had a low intake for many generations.
Recent research
Epidemiologic advances continue: Indicators of population status are increasingly correlated with health outcome measures. In China, Indonesia, Ecuador, Switzerland and Zaire, goitrous communities, or populations with low urinary iodine excretion, have poorer cognition than non-goitrous ones, a condition that has been responsive (in terms of I.Q.) in some studies to iodized salt. New vehicles are being tested, such as irrigation water in China and sugar in Sudan. In Indonesia, supplementing infants with iodized oil reduced mortality < 4 mo of age.