UNIVERSITY PUTRA MALAYSIA

FACULTY OF MEDICINE AND HEALTH SCIENCES

DEPARTMENT OF NUTRITION SCIENCES

IODINE

By

Mohammed Ellulu

MICRONUTRIENTS IN HEALTH AND DISEASE

Introduction

In 1896, Baumann determined the association of iodine with the thyroid gland.

In 1914 Kendall, with revisions by Harrington in 1926, described the hormone complexes synthesized by the thyroid gland using iodine that are so integral to human growth and development.

Recent work has demonstrated iodine, involved through peroxidases in enzymatic activity and production of numerous active metabolites in the human body.

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Absorption, Transport, and Storage

Iodine is usually ingested as an iodide or iodate compound and is rapidly absorbed in the intestine.

Iodine entering the circulation is actively trapped by the thyroid gland.

The active transport of iodine is likely to be based on cotransport of sodium and iodine in capillaries.

Anion thiocyanate inhibits the active transport.

In addition to trapping iodine in thyroid cells, follicular cells also synthesize the glycoprotein, thyroglobulin (Tg), from carbohydrates and amino acids (including tyrosine) obtained from the circulation.

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Thyroglobulin moves into the lumen of the follicle where it becomes available for hormone production.

Thyroid peroxidase (TPO), a membrane-bound hem-containing glycoprotein, catalyzes the oxidation of the iodide to its active form, I2, and the binding of this active form to the tyrosine in thyroglobulin to form mono- or diiodotyrosine (MIT or DIT).

These in turn combine to form the thyroid hormones triiodothyronine (T3) and thyroxine (T4).

Absorption, Transport, and Storage 4

Tyrosine and Thyroxine (T4) 5

Thyroid gland 6

Recommended Intakes

Table 1: Recommended Dietary Allowances (RDAs) for Iodine

Age Male Female Pregnancy Lactation

Birth to 6 months 110 mcg* 110 mcg* (* Adequate intake)

7–12 months 130 mcg* 130 mcg*

1–3 years 90 mcg 90 mcg

4–8 years 90 mcg 90 mcg

9–13 years 120 mcg 120 mcg

14–18 years 150 mcg 150 mcg 220 mcg 290 mcg

19+ years 150 mcg 150 mcg 220 mcg 290 mcg

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Sources of Iodine

Food

Seaweed (such as kelp), seafood, dairy products.

Ionized-Salt

More than 70 countries, including the United States

and Canada, have salt iodization programs.

FDA approved potassium iodide and cuprous iodide

for salt iodization while the WHO recommends the

use of potassium iodate due to its greater stability.

Supplements

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Iodine Deficiency

Iodine deficiency has multiple adverse effects on growth and development, and is the most common cause of preventable mental retardation in the world.

Resulted mainly from inadequate thyroid hormone production.

During pregnancy and early infancy, iodine deficiency can cause irreversible effects.

Under normal conditions, the body tightly controls thyroid hormone concentrations via TSH.

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TSH secretion increases when iodine intake falls below about 100 mcg/day.

TSH increases thyroidal iodine uptake from the blood and the production of thyroid hormone.

However, very low iodine intakes can reduce thyroid hormone production even in the presence of elevated TSH levels.

If iodine intake falls below approximately 10–20 mcg/day, hypothyroidism occurs.

Goiter is the earliest clinical sign of iodine deficiency.

Iodine Deficiency 10

Iodine Deficiency

In pregnant women, iodine deficiency can cause major neurodevelopmental deficits and growth retardation in the fetus, as well as miscarriage and stillbirth.

Chronic, severe iodine deficiency in utero causes cretinism (mental retardation).

Stunted growth, delayed sexual maturation.

In infants and children, less severe iodine deficiency can cause neurodevelopmental deficits such as somewhat lower-than-average intelligence.

Mild to moderate maternal iodine deficiency associated with an increased risk for attention deficit hyperactivity disorder in children.

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Classification of hypothyroidism 12

3ry

2ry

1ry

4ry

Iodine and Health

Fetal and infant development

During early pregnancy, the fetus depends entirely

on maternal T4 and maternal iodine intake.

Production of T4 increases by approximately 50%

during pregnancy, requiring a concomitant increase

in maternal iodine intake.

Breast milk contains iodine, although concentrations

vary based on maternal iodine levels.

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Iodine and Health

Fibrocystic breast disease

Is a benign condition characterized by lumpy,

painful breasts and fibrosis. It affects women of

reproductive age, also occur during menopause,

especially in women taking estrogens.

Breast tissue has a high concentration of iodine,

especially during pregnancy and lactation.

Some research suggests that iodine supplementation

might be helpful for fibrocystic breast disease.

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Radiation-induced thyroid cancer

Thyroidal uptake of radioactive iodine is higher in

people with iodine deficiency than in people with

iodine sufficiency.

The FDA has approved potassium iodide as a

thyroid-blocking agent to reduce the risk of thyroid

cancer in radiation emergencies involving the

release of radioactive iodine (as nuclear accidents).

Iodine and Health 15

Assessment of Iodine Status

There are several additional indicators that are used to

assess thyroid function, such as T4 and T3, but these are

less accurate in reflecting iodine status since conversion

of T4 to T3 and cellular uptake is so responsive to

peripheral need.

Urinary iodine reflects iodine sufficiency, and output

decreases with diminished intake.

Thyroid size, either estimated by palpation or using

ultrasound volume determination, reflects iodine status

since deficiency results in thyroid enlargement, or goitre.

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Assessment of Iodine Status 17

In adults, where long-standing thyroid enlargement from iodine deficiency may be minimally responsive to corrected iodine intake, palpation may be misleading and could overestimate the current level of iodine sufficiency.

TSH is produced in response to decreased iodine intake and diminished thyroid hormone production and is used as a measure of iodine status.

Uptake of radioactive iodine isotopes can be used to scan the gland, and determine the affinity of the gland to introduced iodine, and is a measure of deficiency.

Iodine interaction 18

Major Highly clinically significant. Avoid combinations; the risk of

the interaction outweighs the benefit.

Moderate Moderately clinically significant. Usually avoid

combinations; use it only under special circumstances.

Minor Minimally clinically significant. Minimize risk; assess risk

and consider an alternative drug, take steps to circumvent the

interaction risk and/or institute a monitoring plan.

Iodine interaction 19

Medications for an overactive thyroid (Antithyroid

drugs) Interaction Rating Major.

Taking iodine along with medications for an

overactive thyroid might decrease the thyroid too

much.

Some of these medications include methimazole,

and potassium iodide.

Iodine interaction 20

Amiodarone Interaction Rating: Moderate.

Amiodarone contains iodine. Taking iodine supplements along with amiodarone might cause too much iodine in the blood. Too much iodine in the blood can cause side effects that affect the thyroid.

Medications for high blood pressure (ACE inhibitors) Interaction Rating: Moderate.

Decreases quickly the body gets rid of potassium. Most iodide supplements contain potassium. Taking potassium iodide along with some medications for high blood pressure might cause too much potassium in the body.

Iodine interaction 21

Selenium is required for converting of thyroxine (T4) to triiodthyronine (T3); the removal of iodine molecule from T4.

The iodine molecule that is removed gets returned to the body's pool of iodine and can be reused to make additional thyroid hormones.

If body is deficient in selenium, the conversion of T4 to T3 is slowed, and less iodine is available for the thryoid to use in making new hormones.

Animal studies have shown that arsenic interferes with the uptake of iodine by the thyroid, leading to goiter.

In addition, dietary deficiency of vitamin A, vitamin E, zinc and/or iron can exaggerate the effects of iodine deficiency.

References 22

1. National Research Council, Committee to Assess the Health Implications of Perchlorate Ingestion. Health Implications of Perchlorate Ingestion. Washington, DC: The National Academies Press, 2005.

2. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001.

3. World Health Organization. United Nations Children's Fund & International Council for the Control of Iodine Deficiency Disorders. Assessment of iodine deficiency disorders and monitoring their elimination. 3rd ed. Geneva, Switzerland: WHO, 2007.

4. Patrick L. Iodine: deficiency and therapeutic considerations. Altern Med Rev. 2008 Jun;13(2):116-127.

5. Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408.

6. Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet. 2008 Oct 4;372(9645): 1251-1262.