About Iodide: A Friendly and Necessary Ion

Special Article - Thyroid Gland

Annals Thyroid Res. 2019; 5(3): 223-228.

About Iodide: A Friendly and Necessary Ion

Maria Lúcia1* and Navarro AM2

1Departamento de Clínica Médica, Universidade de Ribeirão Preto (UNAERP), Brazil

2Departamento de Ciências da Saude, Faculdade de Medicina de Ribeirão Preto (FMRP), Brazil

*Corresponding author: Maria Lúcia D’Arbo Alves, Departamento de Clínica Médica, Universidade de Ribeirão Preto (UNAERP), Ribeirão Preto, São Paulo, Brazil

Received: August 06, 2019; Accepted: August 23, 2019; Published: August 30, 2019


Iodide is an essential micronutrient present in very small quantities in the human body, with a fundamental action for the adequate synthesis of thyroid hormones, which are critical for cell differentiation, growth and metabolism. In the form of iodide, iodine is widely distributed in the environment, although in an irregular manner, occurring in abundant amounts in the oceans and in coastal areas and scarcely found on islands and mountains. The diet is the main source of iodine, whose intake varies according to the amount present in soil and water and according to eating habits. Governmental policies have been adopted to satisfy and guarantee the necessary daily supply of iodine, such as fortification of industrialized salt for domestic iodine consumption or addition to the bread commonly consumed in a given region, or the offer of iodized oil to the population, or even iodine supplementation through medications. Iodide deficiency is the main avoidable cause of brain damage to fetuses and children, as well as retardation of psychomotor development. Thyroid hormones are almost universally involved in the development and proliferation of fetal neural tissue. Permanent lesions of the cerebral cortex, hippocampus and cerebellum may occur, with loss of, or damage to the brainstem or spinal cord, affecting cortical areas that integrate highly specialized stimuli, which become poorly defined on an anatomical basis, including silent areas of the associative cortex. One of the more significant metabolic problems due to dietary iodine deficiency is the presence of goiter (increased volume of the thyroid gland). Thyroid carcinoma is the most frequent endocrine neoplasia affecting the human species and plasma iodine concentration is related to the development of specific subtypes of this neoplasia. An increased prevalence of follicular carcinoma, a more aggressive tumor, has been observed in areas of iodine deficiency, while the correction of this deficiency is associated with a higher prevalence of papilliferous carcinoma, a less aggressive form.

Conclusion: An ideal plasma iodide concentration is necessary to insure the proper mental development of fetuses and young children and to minimize the aggressiveness of thyroid cancer from follicular cells in humans.

Keywords: Iodide; Salt iodination; Ioduria; Iodide deficiency; Goiter; Thyroid cancer


Iodine, from the Greek “iodes”, which means “violet” [1], is an essential micronutrient present in very small quantities in the human body (0.02285X10~3% adult body weight) [2,3]. It is consumed in the water or in food as iodine (element with no charge) or iodide (ion with a negative charge), which is converted to iodine in the stomach.

Iodine is a fundamental nutrient for the appropriate synthesis of thyroid hormones, which are critical for cell differentiation, growth and metabolism. It represents 65% of the molecular weight of Thyroxine (T4) and 59% of Triiodothyronine (T3) [4,5]. In the iodide form, iodine is widely distributed in the environment, although in an irregular form, being found in abundant quantities in the oceans and coastal areas and in scarce amounts on islands and mountains [6].

The diet and food supplements containing iodine are the main source of iodine, and its plasma levels are also partially replaced by iodothyronine deiodization in the thyroid cells [6-11].

For many years iodine deficiency was believed to be a problem limited to certain geographic regions and to some special situations (nutrition or malnutrition) and was considered to have a specific clinical spectrum (hypothyroidism, goiter and brain damage, with the possible occurrence of cretinism) [12-14]. However, the reemergence of iodine deficiency has been observed in certain areas of industrialized centers, raising concern about its cognitive consequences [15,16].

This essentiality of iodine is more evident during the initial stages of intrauterine life, implying the need for an adequate iodine intake during pregnancy in order to obtain optimum fetal neurodevelopment. The fetus, followed by the newborn and the child in the first stages of life, represent the phases most vulnerable to iodine deficiency [17].

The first 1000 days of life are considered to be the window of opportunity for potential interventions in the prevention of damage to the human neurological potential, with consequences for the intelligence quotient (IQ) or hyperactivity with attention deficit [17].

Iodine intake varies according to the quantity of iodine in the soil and water and to the eating habits of a given region [11-13].

The World Health Organization (WHO), the United Nations Children’s Fund (UNICEF) and the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) recommend an iodine intake of 90 mg/day for children aged 0 to 5 years, of about 120 μg /day for children aged 6 to 12 years, of 150 μg/day for adults older than 12 years, and of 250 μg/day for pregnant and lactating women [18].

In a study on Latin America, the mean iodine content in the salt varied outside the recommended 20-40 parts per million (ppm), and was greater than 78 ppm in 83% of all samples, demonstrating achievement in the elimination of iodine deficiency in most of the countries studied [19].

From 2005 on, the WHO determined that each country should make its own reports on the iodine deficiency situation every 3 years. Founded in 1986, the Iodine Global Network (IGN) is now the authoritative voice for iodine nutrition.

Iodine requirements increase during pregnancy not only because of the fetal needs, but also because of the change in maternal thyroid physiology. Pregnancy is accompanied by significant changes in thyroid function. During the first phase of gestation, the chorionic gonadotropin produced by the placenta stimulates the maternal thyroid, exerting an effect resembling that of Thyroid-Stimulating Hormone (TSH) due to the structural homology between the molecules, directly stimulating the maternal thyroid. During this period, the fetal thyroid is fully dependent on the maternal thyroid [10,20-22]. Although the fetal thyroid starts its activity between the 18th and 20th weeks of pregnancy, the fetal iodine supply continues to depend on the mother [23].

Gestation involves a high thyroid hormone demand and in pregnant women who ingest an adequate quantity of iodine the release of thyroid hormone reaches a new balance which is maintained until the end of pregnancy. The increased thyroid hormone requirements are satisfied by a proportional increase in the synthesis and release of these hormones which directly depend on maternal iodine intake and, the greater the iodine deficiency, the worse the maternal-fetal consequences [10,14,15,24-26]. An inadequate thyroid response has been observed in healthy pregnant women residing in areas of medium to moderate iodine deficiency [24-26] (Figure 1).

Citation: Lúcia M and Navarro AM. About Iodide: A Friendly and Necessary Ion. Annals Thyroid Res. 2019; 5(3): 223-228.