Micronutrient-Iodine

Iodine

Early in the 1920s, a voluntary salt iodization program was launched to help Americans consume adequate amounts of iodine, an essential micronutrient not commonly found in food.

Iodine is needed for the synthesis of thyroid hormones and critical for normal neurodevelopment in utero yet approximately 60 percent of pregnant women worldwide fall short of meeting the World Health Organization (WHO) requirements (1).

Deficiency in utero can cause irreversible brain damage; it is recognized globally as one of the most common cause of preventable brain damage.(1)

Previously thought to only be of concern in third-world countries. There has been a resurgence of interest in iodine because of its vital role in optimal brain development during pregnancy and postnatal life (1,2)

Today iodine deficiency remains a significant health problem. (3)

Roles in health:

Seventy-five percent (15-20mg) of total body iodine is stored in the thyroid
allowing the thyroid gland to make hormones necessary for a wide variety of physiologic processes including growth, reproductive function, brain development, healing, energy metabolism, central nervous system and healthy thyroid function. (4,5)

Iodine is also used to treat diverse conditions including fibrocystic breast disease, inflammatory skin conditions and as an emergency treatment for radiation exposure (5).

When iodine is deficient the results can range from a subtle loss of intelligence quotient (IQ) to the extreme condition of severe mental and physical retardation called cretinism. (1,6)

Recent meta analyses suggests iodine deficiency is a risk factor for thyroid cancer. (7,8)
Some researchers suggest a deficiency may also be linked to prostate, breast, endometrial and ovarian cancers.

Current recommendations:

The Recommended Dietary Allowance for iodine:

Age	Males & Females	Pregnancy	Lactation
Birth to 6 mo	110 mcg*
7–12 months	130 mcg*
1–3 years	90 mcg
4–8 years	120 mcg
9–13 years	90 mcg
14–18 years	150 mcg	220 mcg	290 mcg
19+ years	150 mcg	220 mcg	290 mcg

The WHO recommends 250 mcg per day during pregnancy.

Tolerable Upper Intake Levels

Age

1-8 years old: 200 mcg/d

9-13 years: 300

14 and older: 600

Pregnancy and lactation: 1100

Signs of deficiencies:

The WHO estimated that over 30% of the world’s population have inadequate iodine intake as measured by urinary iodine below 100 micrograms per liter.(9)

The spectrum of iodine deficiency disorders includes mental retardation, hypothryoidismm, goiter (thyroid enlargement) and other growth and development abnormalities. (2, 10) Low levels of thyroid can lead to infertility in women and autoimmune disease of the thyroid thereby increasing risk of thyroid cancer. (8)

The most serious effect of iodine deficiency occurs in utero with damage to the fetus. Low birth weights and decreased child survival may also result. Deficiency during pregnancy and the first two years of life can have negative congnitive consequences resulting in impaired speech development, learning, reading and potentially behavior disorders. (1, 20)

Even mild iodine deficiency during pregnancy can have long-term adverse impacts on fetal neurocognition. During childhood, iodine deficiency has been linked to reduced intellectual and motor performance which can reduce IQ scores by 13.5 points.(11)

Treatment and prevention incorporates iodine supplements and iodized salt.

Adverse effects of too much:

Iodine is likely safe when taken by mouth or applied to skin in recommended amounts.

Excess intakes of iodine can cause some of the same symptoms as iodine deficiency. (4)

Chronic excess iodine intake from iodine rich foods like kelp, supplements or in areas where the water content is high in iodine can cause toxicity. Prolonged use, higher than the safe upper limit, without medical supervision are potentially unsafe. (10)

Nausea, diarrhea, runny nose, headache, and metallic taste are common side effects but in people who are sensitive, iodine can cause more serious problems. Direct application on the skin can cause irritation, allergic reaction and other side effects.

Iodine-induced thyroid dysfunction may occur after exposure to medications such as amiodarone, a medication that is 37% iodine by weight, or after exposure to iodinated radiographic agents.

Any particular populations affected:

Pregnant and lactating women and infants are vulnerable population groups yet many are unaware of the importance and even without signs of deficiency, how fetal development could be affected (1, 13, 14).

The WHO estimates that 37% of school-age children and nearly 2 billion individuals worldwide, do not consume adequate amounts of iodine. (15)

Women following a paleo diet could be at risk of iodine deficiency and are advised to avoid this diet while non-pregnant women should consider supplementation. 16

Food sources and amounts:

Iodine occurs naturally in seawater and in varying amounts in soil. Iodized table salt is a reliable source as are rich food sources however values can vary widely. Most salt used in processing is not iodized. (5,17, 18)

Iodine is not listed on the Nutrition Facts Panel nor in the USDA Nutrient Database at this time. (19)

Excellent sources:

Cod, baked, 3 ounces 99mcg

Yogurt, plain, low-fat, 1 cup 75

Iodized salt, 1.5 g (approx. 1/4 teaspoon) 71

Milk, reduced fat, 1 cup 56

Bread, white, enriched, 2 slices 45

Shrimp, 3 ounces 35

Ice cream, chocolate, 1/2 cup 30

Good sources:

Macaroni, enriched, boiled, 1 cup 27

Egg, 1 large 24

Tuna, canned in oil, drained, 3 ounces 17

Bottom line:

Iodine demands a spotlight and additional research to help the most vulnerable population groups understand and appreciate the importance of consuming adequate amounts.

Salt iodization is an important strategy to ensure safe and effective levels of iodine consumption globally yet it must be balanced with efforts to control and reduce sodium intake. (2) Universal salt iodization and crop agronomic biofortification are promising new programs to add more iodine to the food supply.

Kathleen Zelman, MPH, RDN, is the nutrition director of WebMD.

Sources:

Bouga, M. et al. Iodine and Pregnancy-A Qualitative Study Focusing on Dietary Guidance and Information. Nutrients. 2018 Mar 26;10(4).
Aburto N, Abudou M, Candeias V, Wu T., 2014. Effect and safety of salt iodisation to prevent iodine deficiency disorders: a systematic review with meta-analyses. WHO e-Library of Evidence for Nutrition Actions (eLENA). Geneva: World Health Organization; http://www.who.int/nutrition/publications/micronutrients/effect_safety_saltiodization/en/
The Lancet Diabetes Endocrinology. Iodine deficiency in the UK: Grabbing the low-hanging fruit. Lancet Diabetes Endocrinol. 2016, 4, 469.
Food and Nutrition Board, Institue of Medicine. Iodine. Dietary reference intakes for vitamin A, vitamin K, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanandium, and zinc. Washington, D.C.: National Academy Press; 2001:258-289
National Institutes of Health, Office of Dietary Supplements, Health Professional Fact Sheet https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/#en2
Pearce, E. et al. Global Iodine Nutrition: Where Do We Stand in 2013? Thyroid ; Volume 23, Number 5, 2013.
Zimmerman, M and Galetti, V. Iodine intake as a risk factor for thyroid cancer: a comprehensive review of animal and human studies. Thyroid Research June 18, 2015;8:8
Cao L-Z, Peng X-D, Xie J-P, Yang F-H, Wen H-L, Li S. The relationship between iodine intake and the risk of thyroid cancer: A meta-analysis. Medicine. 2017;96(20)
World Health Organization website: http://www.who.int/nutrition/topics/ida/en/
Linus Pauling Institute, Oregon State University Micronutrient Information Center website: http://lpi.oregonstate.edu/mic/minerals/iodine
Hynes KL, Otahal P, Hay I, Burgess JR. Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort. J Clin Endocrinol Metab. 2013;98(5):1954-1962.
Rohner F, Zimmermann M, Jooste P, et al. Biomarkers of Nutrition for Development—Iodine Review. The Journal of Nutrition. 2014;144(8):1322S-1342S. doi:10.3945/jn.113.181974.
Caldwell KL, Makhmudov A, Ely E, Jones RL, Wang RY. Iodine Status of the U.S.Population, National Health and Nutrition Examination Survey, 2005-2006 and 2007-2008. Thyroid. 2011 Feb 16.
Patrick L. Iodine: deficiency and therapeutic considerations. Altern Med Rev. 2008 Jun;13(2):116-127.
Andersson M, Karumbunathan V, Zimmermann MB. Global iodine status in 2011 and trends over the past decade. J Nutr 2012;142:744–50
Manousou S et al. European Journal of Clinical Nutrition, volume 72, pages 124–129 (2018)
Pehrsson PR, et al. Iodine in food- and dietary supplement–composition databases. Am J Clin Nutr 2016;104(Suppl):868S–76S.
Abby G Ershow, Gay Goodman, Paul M Coates, Christine A Swanson; Research needs for assessing iodine intake, iodine status, and the effects of maternal iodine supplementation, The American Journal of Clinical Nutrition, Volume 104, Issue suppl_3, 1 September 2016, Pages 941S
U.S. Department of Agriculture, Agricultural Research Service. USDA Nutrient Database for Standard Reference, Release 23
Abel, M.; Ystrom, E.; Caspersen, I.; Meltzer, H.; Aase, H.; Torheim, L.; Askeland, R.; Reichborn-Kjennerud, T.; Brantsæter, A. Maternal Iodine Intake and Offspring Attention-Deficit/Hyperactivity Disorder: Results from a Large Prospective Cohort Study. Nutrients 2017, 9, 1239.

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