**2. Iodine deficiency disorders (IDD) and symptoms**

## **2.1 Causes of IDD**

Most of the iodine exists in the ocean and seafood, including saltwater fish, shellfish, kelp, seaweed and seaweed products which can provide a considerable amount of iodine [11]. Iodine exists in the sea and the soil as iodide. Iodide ions are oxidised by sunlight to elemental iodine which is volatile. The iodine cycle in nature is complete if the concentration of iodide in the seawater is about 50–60 μg/L, approximately 0.7 μg/m3 in the air, and the iodine in the atmosphere is returned to the soil through rain, with concentrations in the range of 1.8–8.5 μg/L. Iodine deficiency occurs in the soil when the return of the iodine to the soil is slow and in small amount compared to the original loss of iodine. Hence, all crops grown in this soil will be iodine deficient [12]. Low levels of iodine in the diet for people who do not get enough iodine from their food may lead to health problems collectively referred to as iodine deficiency disorders (IDD) [14].

#### **2.2 The problem of IDD to human population**

IDD is a major public health problem for population throughout the world which affects human from early foetal life through to adulthood [15]. Although IDD can affect any person of any age, pregnant women and children are the most vulnerable high-risk group for IDD [16]. Iodine requirement is high during pregnancy; it may increase by 50% because of increased maternal thyroxine production [14].

IDD in the foetus is the result of IDD in the mother, and this condition is associated with greater incidence of stillbirths, abortions, congenital abnormalities, neurological cretinism and psychomotor defects (**Figure 3**). In neonate, apart from mortality, the continuing severe IDD may affect the brain and physical development. Low birth weight is normally associated with a higher rate of congenital anomalies, and there were also evidences on substantial fall in infant mortality with improved birth weight following the iodized oil injection. IDD in the child and adolescent is associated with juvenile hypothyroidism, impaired mental function and retarded physical development. Studies on schoolchildren living in iodine-deficient areas indicated impaired school performance and IQs [17], while IDD in the adult had effects on their individual capacity, initiative and decision-making (**Figure 3**). These results indicate that IDD can be a major obstacle to human and social development of population living in an iodine-deficient environment. Therefore, correction of iodine deficiency is considered as a major contribution to population development [18].

**17**

**Figure 3.**

*Urinary Iodine: Biomarker for Population Iodine Nutrition*

**3. Iodine needs in pregnant women and their foetuses**

*i.e. foetus, neonate, infant, child, adolescent and adult.*

Pregnant woman is one of the most susceptible groups for iodine deficiency. An adequate intake of iodine in the diet of pregnant woman is important to ensure normal growth and development of the foetus. During pregnancy, iodine requirement increases substantially to ensure adequate supply to the foetus particularly for healthy brain development. Iodine deficiency during pregnancy can cause maternal and foetal hypothyroidism and impairs neurological development of the foetus since it is secondary to transplacental passage of iodide. The consequences depend upon the timing and

*Effect of iodine deficiency and the spectrum of IDD across the life span (clinical presentation) in various age groups,* 

severity of hypothyroidism; the most severe manifestation is cretinism [14].

Since most foods have relatively low iodine content, Universal Salt Iodization (USI) programmes are executed. However, in countries or setting where USI is not possible, other mode of iodine supplementation needs to be implemented. It is difficult to accurately quantify iodine intakes using traditional methods of dietary assessment in terms of the contribution of iodized salt use from table and cooking to total iodine intake. In view of the limitations of dietary assessment for adequate iodine, a mUIC

*DOI: http://dx.doi.org/10.5772/intechopen.84969*

*Urinary Iodine: Biomarker for Population Iodine Nutrition DOI: http://dx.doi.org/10.5772/intechopen.84969*

**Figure 3.**

*Biochemical Testing - Clinical correlation and Diagnosis*

**2. Iodine deficiency disorders (IDD) and symptoms**

larly in neonates [10].

**2.1 Causes of IDD**

(IDD) [14].

production [14].

development [18].

50–60 μg/L, approximately 0.7 μg/m3

**2.2 The problem of IDD to human population**

and physical development [9]. The regulation of thyroid hormones is under the control of the pituitary gland through thyroid-stimulating hormone (TSH). TSH secretion is regulated by a 'feedback' mechanism related to the level of thyroid hormones thyroxine [3,5,3′,5′-tetraiodothyronine (T4)] in the blood. Iodine is needed in the human body, and as the blood T4 falls, the pituitary TSH secretion is increased. In severe iodine deficiency disorders (IDD), the level of T4 remains lowered, and the level of TSH remains elevated. Both these measurements are used for diagnosis of hypothyroidism due to IDD at various stages in life particu-

Most of the iodine exists in the ocean and seafood, including saltwater fish, shellfish, kelp, seaweed and seaweed products which can provide a considerable amount of iodine [11]. Iodine exists in the sea and the soil as iodide. Iodide ions are oxidised by sunlight to elemental iodine which is volatile. The iodine cycle in nature is complete if the concentration of iodide in the seawater is about

sphere is returned to the soil through rain, with concentrations in the range of 1.8–8.5 μg/L. Iodine deficiency occurs in the soil when the return of the iodine to the soil is slow and in small amount compared to the original loss of iodine. Hence, all crops grown in this soil will be iodine deficient [12]. Low levels of iodine in the diet for people who do not get enough iodine from their food may lead to health problems collectively referred to as iodine deficiency disorders

IDD is a major public health problem for population throughout the world which affects human from early foetal life through to adulthood [15]. Although IDD can affect any person of any age, pregnant women and children are the most vulnerable high-risk group for IDD [16]. Iodine requirement is high during pregnancy; it may increase by 50% because of increased maternal thyroxine

IDD in the foetus is the result of IDD in the mother, and this condition is associated with greater incidence of stillbirths, abortions, congenital abnormalities, neurological cretinism and psychomotor defects (**Figure 3**). In neonate, apart from mortality, the continuing severe IDD may affect the brain and physical development. Low birth weight is normally associated with a higher rate of congenital anomalies, and there were also evidences on substantial fall in infant mortality with improved birth weight following the iodized oil injection. IDD in the child and adolescent is associated with juvenile hypothyroidism, impaired mental function and retarded physical development. Studies on schoolchildren living in iodine-deficient areas indicated impaired school performance and IQs [17], while IDD in the adult had effects on their individual capacity, initiative and decision-making (**Figure 3**). These results indicate that IDD can be a major obstacle to human and social development of population living in an iodine-deficient environment. Therefore, correction of iodine deficiency is considered as a major contribution to population

in the air, and the iodine in the atmo-

**16**

*Effect of iodine deficiency and the spectrum of IDD across the life span (clinical presentation) in various age groups, i.e. foetus, neonate, infant, child, adolescent and adult.*

#### **3. Iodine needs in pregnant women and their foetuses**

Pregnant woman is one of the most susceptible groups for iodine deficiency. An adequate intake of iodine in the diet of pregnant woman is important to ensure normal growth and development of the foetus. During pregnancy, iodine requirement increases substantially to ensure adequate supply to the foetus particularly for healthy brain development. Iodine deficiency during pregnancy can cause maternal and foetal hypothyroidism and impairs neurological development of the foetus since it is secondary to transplacental passage of iodide. The consequences depend upon the timing and severity of hypothyroidism; the most severe manifestation is cretinism [14].

Since most foods have relatively low iodine content, Universal Salt Iodization (USI) programmes are executed. However, in countries or setting where USI is not possible, other mode of iodine supplementation needs to be implemented. It is difficult to accurately quantify iodine intakes using traditional methods of dietary assessment in terms of the contribution of iodized salt use from table and cooking to total iodine intake. In view of the limitations of dietary assessment for adequate iodine, a mUIC

of 150–249 μg/L has been established to determine the adequate iodine status among pregnant women. However, the large intra-individual variation in UIC from either spot or 24-hour urine samples means that UIC cannot be used to assess iodine status in an individual pregnant woman. Therefore, the association between iodine status in pregnancy and the developmental outcome of the individual child is rather difficult to be assessed.
