Iodine Deficiency: Consequences and Pregnancy Importance

IODINE AND PREGNANCY IODINE AND PREGNANCY Dr Sedigheh Hantoushzadeh

WHY IODINE IS NECESSORY Iodine is an essential element for human survival since it is essential for making thyroid hormones. Iodine deficiency disorders (IDD) have been recognized as a major public health problem worldwide According to the reports of World Health Organization (WHO) and United Nations Children s Fund (UNICEF), more than 30% of school-aged children (260 million) suffer from insufficient iodine intake

The term "iodine deficiency disorders" (IDD) refers to all of the consequences of iodine deficiency, which depend on its severity and the age of the affected subject Iodine is an essential component of thyroxine (T4) and tri iodothyronine (T3), and it must be provided in the diet. Inadequate iodine intake leads to inadequate thyroid hormone production, and all the consequences of iodine deficiency stem from the associated hypothyroidism. Iodine is particularly important during preconception and the first 16 weeks of pregnancy, when the developing fetus is entirely dependent on the mother for its supply of iodine and the thyroid hormone. This topic will review the consequences of iodine deficiency, its geographical distribution, diagnostic measures, prophylaxis, and treatment.

RESOURSE RESOURSE Iodine can be obtained by consumption of foods that naturally contain it (fish, seafood, kelp, some drinking water, and vegetables grown in iodine-sufficient soil) or to which it is added (iodized table salt or foods enriched with iodine). Cow's milk is a source of iodine owing to iodine in cattle feed and the use of iodophor udder cleansers in the dairy industry. Sea salt naturally contains only a small amount of iodine. Dietary iodine is absorbed as iodide and rapidly distributed in the extracellular fluid, which also contains iodide released from the thyroid and by extrathyroidal deiodination of the iodothyronines. Iodide leaves this pool by transport into the thyroid and excretion into the urine.

IODINE HOMEOSTASIS IN PREGNANCY Physiologic Changes in Pregnancy T4 production increases approximately 50% starting in early pregnancy. High levels of circulating estrogen during pregnancy decrease catabolism of the sialic acid-rich thyroxine- binding globulin (TBG) . Consequently, circulating TBG levels increase 1.5-fold, increasing the levels of circulating total T3 and T4 and requiring an increase in thyroid hormone production to maintain normal unbound thyroid hormone levels Additionally, in early gestation, the thyroid is stimulated not only by TSH but by the alpha subunit of human chorionic gonadotropin (hCG), which also binds to and stimulates the TSH receptor . els

Severe Iodine Deficiency Severe dietary maternal iodine deficiency in pregnancy has the potential to cause both maternal and fetal hypothyroidism. Severe iodine deficiency is associated with poor obstetric outcomes including spontaneous abortion, prematurity, and stillbirth . Thyroid hormone plays an essential role in neuronal migration, myelination, and synaptic transmission and plasticity iodine deficiency is associated with adverse effects on the fetus including congenital anomalies, decreased intelligence, and neurological cretinism (which includes spasticity, deaf mutism, mental deficiency, and squint)

MILD-TO-MODERATE IODINE DEFICIENCY The effects of mild-to-moderate iodine deficiency are less well understood than those of severe iodine deficiency. Minor neuropsychological defects A small study found a significantly greater prevalence of attention deficit hyperactivity disorder (ADHD)

THE WORLD HEALTH ORGANIZATION (WHO) RECOMMENDS A DAILY INTAKE OF THE NATIONAL ACADEMY OF MEDICINE RECOMMENDED MINIMUM DAILY INTAKE OF IODINE 90 mcg for children 1 to 8 years old 90 mcg of iodine for infants and children up to 5 years 120 mcg for children 6 to 12 years 150 mcg for children 12 years and adults 250 mcg during pregnancy and lactation 120 mcg for children 9 to 13 years old 150 mcg for older adolescents and nonpregnant adults 220 mcg for pregnant women 290 mcg for lactating women

ASSESSMENT OF IODINE NUTRITION Neonatal serum TSH Serum Urinary iodine Thyroid size thyroglobulin In practice, urinary iodine is most often used to determine iodine nutrition at the population level. The urinary iodine concentration indicates current iodine nutrition, while thyroid size and the serum thyroglobulin concentration reflect iodine nutrition over a period of months or years.

URINARY IODINE EXCRETION Approximately 90 percent or more of ingested iodine eventually appears in the urine. For assessing the iodine nutritional status of a population, measurements of urinary iodine concentration in randomly collected urine samples have proven to be as useful as measurements of urinary creatinine and iodine and calculation of the iodine-to-creatinine ratio . The results from random samples also correlate well with 24-hour urine collections. As a result, iodine nutrition is often defined by the urinary iodineconcentration in randomly collected urine samples. Mild iodine deficiency is defined as a median urinary iodine concentration of 50 to 99 mcg/L, moderate deficiency as 20 to 49 mcg/L, and severe deficiency as <20 mcg/L

THYROID SIZE Thyroid size is a sensitive marker for iodine deficiency because goiter, although not the most severe consequence of iodine deficiency, is the most clinically evident. Assessment by palpation is too crude to be anything more than qualitative except in severe deficiency, but ultrasonography is precise, quantifiable, and easily performed.

PROPHYLAXIS AND TREATMENT Community Iodine deficiency is a global public health problem and, in combating it, emphasis should be placed on diagnosis and correction at the level of the community rather than the individual. Achieving sufficient iodine nutrition in the population would eliminate the need for specific supplementation during pregnancy and lactation.

DURING PREGNANCY AND LACTATION Consuming an adequate amount of iodine during pregnancy is important for fetal development. The World Health Organization (WHO) recommends iodine supplementation in pregnancy and lactation in regions where <90 percent of households use iodized salt and the median urinary iodine concentration in children is <100 mcg/L . In pregnant women, urinary iodine concentrations of 150 to 249 mcg/L indicate adequate iodine intake. Iodine dosing guidelines are as follows: Iodine supplementation is not necessary in women who are taking levothyroxine for the treatment of hypothyroidism.

The tolerable upper intake amount for iodine, as established by European and United States expert committees, ranges from 600 to 1100 mcg daily for adults and pregnant women >19 years age . The WHO sets the tolerable upper intake amount for iodine as 500 mcg daily for pregnant women, while the IOM uses 1100 mcg daily for adults and pregnant women >19 years of age. Smoking reduces iodine in breast milk due to inhibition of iodine transport into the milk by thiocyanate found in cigarette smoke . For adolescents 15 to 17 years, it ranges from 500 to 900 mcg daily and for younger children, 200 to 450 mcg/day.

In some countries that have mandatory programs of salt iodization, inadequate quality control has caused major fluctuations in dietary iodine intake. Iodine deficiency has recurred in some countries with initially successful programs after a regular follow-up program was abandoned. In Denmark, mothers who smoke have reduced iodine in their breast milk (26 versus 54 mcg/L in nonsmokers despite identical urine iodine concentrations), and their infants have reduced urinary iodine concentrations (33 versus 40 mcg/L in nonsmokers) . Potential contributing factors include a decrease in salt intake, a reduction in the use of iodine salts in the baking industry, and undoubtedly other unidentified commercial and environmental factors. Smoking cessation efforts are important in this population. Sustaining iodine sufficiency Regular monitoring of iodine nutrition is essential for sustaining iodine sufficiency .

Adverse effects Iodine repletion in the doses used for iodization of salt and in prenatal supplements has few adverse effects Iodine administration may result in clinically significant hyperthyroidism in patients with endemic goiter or in patients with nodular goiters containing autonomously functioning tissue. In contrast, iodine administration may induce or exacerbate hypothyroidism in patients with underlying autoimmune thyroiditis .

Maternal and neonatal outcomes and determinants of iodine deficiency in third trimester of pregnancy in an iodine sufficient area Soraya Saleh Gargari, Reyhaneh Fateh, Mina Bakhshali-bakhtiari, Masoumeh Saleh, Masoumeh Mirzamoradi & Mahmood Bakhtiyari BMC Pregnancy and Childbirth volume 20, Article number: 174 (2020) Iodine deficiency in pregnant women can be improved by appreciate planning for pregnancy, proper inter-pregnancy time interval (> 12 months to < 5years), appropriate nutrition during pregnancy. Besides, controlling maternal urinary iodine concentrations is important to prevent neonatal complications such as preterm delivery and NICU admission.

Review of Iodine Nutrition in Iranian Population in the Past Quarter of Century Hossein Delshad1and Fereidoun Azizi1,*2017 The success of iodine deficiency control program depends on well designed programmatic steps and mandatory iodized salt consumption in certain situations. The iodine intake of school children is sufficient, however, Iranian pregnant women are suffering from moderate iodine deficiency and need iodine supplementation.

Appropriate Iodine Nutrition in Iran: 20 Years of Success Hossein Delshad 2010 Iodine Deficiency Disorders in the South of Iran during 1989-2012: A Surveillance System Report Alireza Mirahmadizadeh1 , Elham Kavoosi2, Marzieh Vakili2, Razieh Shenavar2, Mohsen Moghadami

Evaluation of Iodine Nutritional Status in Tehran, Iran: Iodine Deficiency Within Iodine Sufficiency Pantea Nazeri Parvin Mirmiran Yadollah Mehrabi Mehdi Hedayati Hossein Delshadand Fereidoun Azizi Mild iodine deficiency has recurred in Tehranians. The results emphasize the need for continuous monitoring in all regions, even in a country with iodine sufficiency.