Iodine Disorders

INTRODUCTION
Iodine deficiency disorders are still very much prevalent in the world today. Two billion people, estimated by the WHO, still lack a sufficient level of iodine in their diets which leads to a range of disorders known as iodine deficiency disorders (IDD).
So what is iodine? Iodine is an essential micronutrient in the diet which is used by the thyroid gland (located in the throat) to produce thyroid hormones which help control the body’s metabolism. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3).
Thyroxine has four iodine molecules attached to it’s structure, while triiodothyronine has three iodine molecules attached to it.
Iodine deficiency has a major negative effect on growth and
development and is one of the main causes of preventable mental retardation throughout the world. Although it is still a major worldwide health problem, the number of countries where iodine deficiency is a public health problem has halved in number over the past ten years to 54 countries, according to a new global report on iodine status.
IODINE REQUIREMENTS
Since 1989, the Food and Nutrition Board of the U.S. National Academy of Sciences,
National Research Council have recommended the following daily iodine intakes:
Age/Range/State Intake (μg/day)
0-12 months 50
1-6 years 90
7-12 years 120
12+ 150
Pregnancy 200
Lactation 200
These RDAs are the same value for both males and females.
Previous WHO/ICCIDD (International Council for the Control of Iodine Deficiency
Disorders) meetings suggested that iodine requirements for newborns, pregnant and lactating women be increased to a higher RDA. Some suggestions also from other councils were to increase the RDA to 250-300μg/day for pregnant women, 225-350μg/day for women during lactation and 90μg/day for infants.
However there is also an issue of iodine toxicity caused by the consumption of too much iodine. According to Wolff, intakes of 2000μg/day are regarded as excessive and potentially harmful, risking the onset of hyperthyroidism. Normal diets composed of natural foods are unlikely to supply such a high amount of iodine but diets rich in marine fish and seaweed like those of Japan, can supply up to an extremely high amount of 50,000μg/day.
THE FETUS
Iodine deficiency disorders in the fetus result from iodine deficiency in the mother’s diet. Iodine deficiency in the fetus is associated with a higher incidence of still births, abortions, congenital abnormalities, increased perinatal mortality, increased infant mortality, neurologic cretinism, hyperthyroid cretinism, psychomotor defects and increased susceptibility of the thyroid gland to nuclear radiation.
All of these conditions can be reduced and even prevented by a correct iodine value in the mother’s daily nutritional intake.
The most severe disorders caused by iodine deficiency is cretinism. This condition occurs when the iodine intake is below 25μg/day. Cretinism, in it’s most common form, has typical features of either a predominant neurological syndrome with severe to intense mental retardation. This includes deaf-mutism (speech and hearing defects) squint and disorders of stance and gait of varying intensity. Myxedematous cretinism, which is less common, shows predominant features of hyperthyroidism and dwarfism with less severe mental
retardation.
Cretinism is still widely prevalent, affecting up to 10% of those living in severe iodine deficient areas such as parts of India, Indonesia, China, Africa and the Andean region in South America. In Europe, during the 19th and 20th centuary, cretinism spontaneously disappeared in Europe. This disappearance is now attributed to increased dietary iodine from new nutritionally balanced diets and use of iodine supplements during pregnancy, associated with economic development.
THE INFANT
Increased perinatal mortality due to iodine deficiency has been shown in Zaire from results of a controlled experiment of iodized oil injections which alternate with a control injection gicen to the mother in the latter half of pregnancy. Results of this experiment showed that, following the iodized oil injection, infant mortality fell substantially, a second positive result also emerged from this experiment as there was an improvement in the birth weights of infants. Low birth weight is generally associated with a higher rate of congenital abnormalities and a higher risk through childhood. This has been demonstrated in the long term follow up study of the controlled trial in Papua New Guinea in children up to the age of 12 years. A reduction of infant mortality has also been evident in China following iodine supplementation of irrigation water in areas of severe iodine deficiency.
Aside from infant mortality, the importance of thyroid function in the infant is because the brain size of the infant when born is only half the size of an adult brain. The infant’s brain grows rapidly in size until the infant reached about 2 years old. Thyroid hormone, which is dependent on an adequate supply of iodine, is vital for normal brain development and has been proved by various studies on animals. Due to the brain’s need for thyroid hormone, sufficient dietary iodine intake is required to maintain a normal functioning thyroid gland. Severe deficiency poses a threat to neonatal thyroid function and therefore poses a threat to early brain development.
Another series of tests concerning iodine deficiency in infants were carried out in Europe. Urine samples from several European countries were collected and analysed. Some very high levels of urinary iodine were observed in Rotterdam, Helsinki and Stockholm. When iodine intake is about a third of the RDA in infants, Hyperthyrotropinemia (which is high levels of serum TSH) with the risk of brain damage occurs and dramatic neonatal hypothyroidism resulting in endemic cretinism occurs when intake is one tenth of the RDA. When the urinary iodine concentration of young infants is below 50-60μg/l, corresponding to an intake of 25-35μg/day (15-5μg/day under the RDA for infants),there is a sudden increase in the prevalence of neonatal serum TSH values in excess of 50mU/ml which indicates sub-clinical hypothyroidism and eventually, if untreated, worsens to transient neonatal hypothyroidism. When urinary iodine concentration is measured at 10-20μg/l in severe endemic goitre regions, it is observed that up to 10% of infants have severe hyperthyroidism with serum TSH levels above 100mU/ml and serum T3 values below 30μg/l. If this problem is not recognised and treated, these infants develop to myxedematous endemic cretinism.
Another important aspect of iodine deficiency in infancy is an increased susceptibility of the thyroid gland to radioactive fallout.
Thyroidal uptake of radioiodine reaches its maximum value in the infancy years and then declines progressively into adult life. It was estimated that the turnover rate for intra-thyroidal iodine must be 25 to 30 times higher in young infants than the rate in humans over 12 years old. In iodine deficiency a further increase in turnover rate is required to maintain normal thyroid hormone levels. This is the reason for a greatly increased susceptibility of the infant to iodine deficiency. Iodine deficiency also causes increased uptake of radioiodide resulting from exposure to nuclear radiation, as occurred in the Chernobyl disaster. Protection against this increased uptake can only be provided by correction of iodine deficiency in the
diet.
THE CHILD
Iodine deficiency in children is usually associated with goitre. Goitres are formed by enlargement of the thyroid gland. Iodine deficiency leads to a decrease in T4 production which causes an increase in TSH production in the pituitary gland. An increased TSH level stimulates the thyroid follicles to enlarge and multiply giving the characteristic goitre appearance of a swollen throat. Without the ability to increase hormone production because of iodine deficiency, the gland becomes hyperplastic. Problems such as blockage of the oesophagus and trachea and damage to the laryngeal nerves can occur with very large goitres. Some forms of goitre however can only be detected by touch.
The goitre rate increases as a child gets older and reaches a maximum in adolescence. Girls tend to have a higher prevalence to goitre than boys do. Goitre rates are sometimes studied in schools amongst children between the ages of 8 and 14. This provides an indication of the presence of iodine deficiency in an area. School children living in iodine deficient areas show lower academic performances and lower IQs compared against similar groups in iodine sufficient areas. These tests are difficult to carry out due to the difficulty in sourcing a correct control group.
Unlike the iodine sufficient area, more than likely the iodine deficient area is going to be more remote and have poorer school facilities with its pupils being from a worse economic background and having a poorer quality nutritional diet. However all of these factors are taken into account during these tests. In a metaanalysis of 18 studies with comparisons between both groups of iodine sufficient and iodine deficient, mean scores differed by 13.5 IQ points which is quite a significant amount.
Treatment with iodine supplements in older children and even adults can reverse many of the clinical manifestations of iodine deficiency disorders.
THE ADULT
In iodine deficient areas, iodine administration in the form of iodized salt, bread and oil is effective in the prevention and the reduction of goitre. Iodized oil injections seem to be the most effective method as the obvious effects of the injection leads to acceptance by people and therefore a greater demand in iodine deficient communities. A rise in thyroxine in the body is seen after iodine is administrated by various means.
Cerebral hypothyroidism is an effect in the adult that may not be as easily identifiable as goitre. This is characterised by slower responses and slower reaction times. As the brain is extremely sensitive to hypothyroidism, impaired brain function occurs before the functions of other organs are more visibly noticed. Recent findings from studies in thyroid physiology and biochemistry have explained this clinical observation. The major determinant of the brain, and the pituitary gland, T3 is serum T4, not serum T3 (as is true for other organs). Low levels of brain T3 have been demonstrated in experiments carried out on iodine deficient laboratory rats in association with reduced levels of serum T4 and have been restored to normal with the correction of the iodine deficiency in the dietary uptake. These findings explain suboptimal brain function in humans with endemic goitre and lowered serum T4 levels and its improvement following correction of iodine deficiency.
A high degree of apathy amongst adults was noted in populations in iodine deficient areas of northern India. This reduced mental function is caused by cerebral hypothyroidism. It has been shown that, on elimination of iodine deficiency by administrating iodine to subjects by different mediums, the capacity for initiative and decision-making improved. Iodine deficiency is a major obstacle to human and social development in areas of low iodine levels. Correction of this iodine deficiency makes a large contribution to the brain development and also reduces susceptibility to nuclear radiation.
It is noted that in adulthood, the consequences of iodine deficiency are more serious in women, especially during pregnancy, than in men.
CORRECTION OF IODINE DEFICIENCY
Prevention is better than a cure, so it is advisable to be aware of your dietary iodine intake. Plants and cereals can contain up to 1mg/kg of iodine, depending on how iodine sufficient the soil they grew on was. Iodine has also been added to water sources and irrigation schemes. In Europe, cow’s milk has become a major source of iodine (0.15mg/kg) due to the use of supplemented feeds and the giving of iodinated casein as a lactation promoter. The richest sources of iodine however are found in marine fish (2.5mg/kg) shellfish (1.6mg/kg) seaweed (5mg/kg) and sea salt (1.4mg/kg). Iodine is also provided in multivitamin tablets and in sea kelp products.
In developing countries, different measures of iodine supplementation have had to taken place as people do not have as a nutritionally balanced and stable diet as they do in developed countries. Long term dietary iodine replacement at levels recommended by the WHO may decrease the size of goitres in those who suffer from it. Generally long term goitres only respond showing small decreases in size after supplementation, and the patient has a risk of developing hypothyroidism. Three methods in particular have been a noted success.
Iodized salt used in food preparation is one of the best ways to obtain an adequate intake of iodine as it contains 76μg/g of salt. It was first successfully used in Switzerland in the 1920s. Since then it has been successful in America, Finland, China and Taiwan. Due to difficulties in maintaining a steady production and supply of iodized salt, a universal salt iodized policy in many countries was adopted by many nations. This has enabled over 80% of the human population access to iodized salt, costing the minute amount of 4cent per person per year . This is certainly cheaper than social and healthcare prices of treating areas of iodine deficiency. Salt should be added after cooking to ensure no iodine loss occurs so some cost is needed to educate people on the use of iodized salt.
Iodized oil by injection has proven to be a popular method in third world countries as it can last for up to 4 years and shows a rapid regression of goitre after receiving the injection. In and iodine deficient area, the oil which is made up of 1ml of poppyseed oil and 480mg of iodine, is administered to all females up to the age of 40 and all males up to the age of 20. The injection is required every 3-5 years depending on the subject’s age and the previous dose they received. Children have a greater need than adults do and the dose should be repeated every 3 years in deficient areas.
Iodized oil by mouth is a less effective method as it only lasts half as long as the iodized oil injection. It has seen an increasing trend however due to the hazards associated with injections. A recent study in children showed that 1ml of oral oil that contain 480mg of iodine, provides protection against iodine deficiency for 1 year.
I have learned quite a substantial amount about the importance of iodine in the diet from researching this essay. It is interesting to discover that for only 4cent per person, a sufficient supply of iodine can be supplied and prevent some very serious deficiency disorders. It is shocking to see that for such a small price, more money is not invested into providing 100% of the human population access to iodized salt and preventing some extremely difficult lifestyles for people suffering from disorders such as cretinism.
References
NT2002 Minerals Section Manual – Dr. Tom O’Connor
Modern Nutrition in Health and Disease 9th edition (Chap. 13) – Shils, Olson et al. www.WHO.org emedicine.medscape.com