THYROID AND IODINE: ARE YOU GETTING ENOUGH IODINE ?

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Iodine is an essential component of thyroid hormone production.Iodine is the naturally occurring element, which is a solid at room temperature. Iodide is the form when it combines with another element like potassium or sodium, which is usually what is added to iodised salt.Most iodide is found in the oceans and evaporates into the atmosphere and is returned to the soil by rain. Soil and groundwater can become iodine deficient because the iodine cycle is not as efficient in many geographical regions of the world.Iodine deficiency is common in many hilly and mountainous regions of the world.
IODINE DEFICIENCY DISEASES:
Iodine deficiency is associated with many conditions, all of them related to thyroid function.
In Adults:
  • Goitre
  • Hypothyroidism
  • Impaired mental function.

In pregnancy:

  • Miscarriage
  • Stillbirths
  • Congenital anomalies.
In newborns and children:
  • Cretinism
  • Mental retardation
  • Neonatal goitre
  • Neonatal hypothyroidism.
  • Developmental delay
The biggest problem of iodine deficiency occurs when pregnant women are deficient in this mineral, because mental retardation in the child as a result of iodine deficiency is irreversible.Studies have shown that even in mildly iodine deficient women children were born with lower IQ.
WHERE DO YOU GET YOUR IODINE?
Your body does not make iodine so you have to get it from food or supplements.Iodine content in food can vary because the quantity present in soil varies.
The commonest sources of iodine are:
  • Seaweeds like kelp, nori,wakame.
  • Eggs, dairy.
  • Some fish
  • Iodized salt
  • Supplements

IODIZED SALT:

Worldwide iodine deficiency diseases are still a major public health problem in many countries.Mountainous areas, such as the Himalayas, Alps, and Andes regions, and river valleys prone to flooding, especially in South and Southeast Asia, are among the most iodine-deficient regions in the world.To counter the adverse effects of this condition the program of salt iodization was started in many countries.

Salt iodization is a process whereby potassium iodide is added to common salt during the manufacturing process so that people consuming adequate amounts of iodized salt will not be iodine deficient. Iodized salt was first available in the United States in 1924. Though populations  in United States and Canada are considered to have adequate iodine levels, according to the Statistics Canada website,a 2009 study among Canadians aged 3 to 79, showed that a moderate deficiency of urine iodine levels was found in 7% of the population while 15% had an excessive intake.A deficiency and an excess are both cause for concern.
 In India several studies have shown that despite a program of salt iodization since the 1960ties, goiter and other Iodine Deficiency Disorders still remain a problem in many regions.

HOW MUCH IODINE DO YOU NEED IN A DAY?

The standard recommendation is:

  • Non-pregnant adults 150 microgram/day
  • Pregnant and breast feeding women 250 microgram/day. However, the recommendations for the upper limit vary from 500-1,100 mcg of iodine daily.
  • Tolerable upper limits of iodine intake: 1100 microgram/day

CAN YOU GET ADEQUATE IODINE FROM IODIZED SALT?

This is open to debate because of various reasons. The amount of iodine present in the iodized salt depends on the conditions of storage, relative humidity and the packaging material used. In fact, a 2008 study from the US states that “Forty-seven of 88 samples (of Iodized salt) fell below the USFDA recommended Iodine content while 6 exceeded it.” 

The World Health Organization (WHO) recommends that you should take 5 grams of salt a day. This quantity of iodized salt should ideally contain 400 microgram of Iodine. However, most people use a lot more salt than the recommended 5 grams. A lot of the salt intake is from processed food which is not iodized salt. Excess salt has been associated with higher incidence of high blood pressure.

Instead of getting your iodine from iodized salt perhaps it is better to get it from a multivitamin multimineral supplement containing 150 microgram of Iodine.

IS THERE A PROBLEM OF TOO MUCH IODINE?

According to the American Thyroid Association (ATA) the tolerable upper limit of iodine intake is 1100 microgram per day. In fact, the ATA advises against the ingestion of iodine and kelp supplements containing in excess of 500 mcg iodine daily. A study from China in The American Journal of Clinical Nutrition (2012) shows that amongst euthyroid (normal thyroid function) adults subclinical hypothyroidism appeared in the participants who took 800 μg/d of Iodine.

Therefore, excess iodine intake can be harmful and has been associated with :

  • Hyperthyroidism
  • Hypothyroidism
  • Congenital hypothyroidism because of excess Iodine intake by mother.

High doses of Iodine are sometimes recommended by some practitioners. It is often quoted that the Japanese people living in Japan consume very high amounts of Iodine through their diet of seaweed. Is it possible that the Japanese people have a different gut microbiota which helps them process the excess iodine differently? (Reference: Dr. Justin Sonnenburg, PhD, “Microbiology: genetic pot luck.” Drs Justin and Erica Sonnenburg have written an excellent book The Good Gut: Taking Control of Your Weight, Your Mood and Your Long-term Health)

High doses of iodine are appropriate in the treatment of severe hyperthyroidism before thyroid surgery and as potassium iodide following a nuclear accident. However, this is always done by a qualified physician.

HOW DO YOU KNOW IF YOU HAVE IODINE DEFICIENCY?

This question does not have a simple answer.

Urine Iodine Concentrations: Iodine levels cannot be reliably measured in individuals because of the considerable day-to-day variation in iodine intake. Median urinary iodine concentrations (UIC) have been widely used as a biomarker of population iodine intake. This does not necessarily apply to individuals.

Thyroglobulin: Serum thyroglobulin can be used as a marker of iodine levels in the body. However, this is not a test in isolation of other thyroid function tests. Sometimes Anti Thyroglobulin Antibodies may interfere with the test result. Also keep in mind that Thyroglobulin is not a test for thyroid cancer. (Thyroid Function Tests)

Dried Urine Iodine Test: This test is easily available in USA and Canada and is done by special laboratories. Though not done in India, samples can be shipped to USA and tested. Some testing companies also test Bromine, Fluorine, Thyroglobulin, and some heavy metals in addition to Iodine.

KEY POINTS

  • Iodine is very important for thyroid health.
  • Low iodine in pregnant women is avoidable but irreversible cause of mental retardation in children.
  • Pregnant women must ensure adequate iodine intake BEFORE pregnancy. Extra iodine is needed during pregnancy and breast feeding. Check your antenatal vitamins contain adequate iodine.
  • Iodine deficiency exists even in iodine-adequate countries.
  • Excess iodine intake has adverse effects.
  • Iodized salt may not be best source of iodine.
  • Supplement with multivitamin multimineral containing at least 150 micrograms of Iodine.

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REFERENCES 

  1. http://www.statcan.gc.ca/pub/82-625-x/2012001/article/11733-eng.htm
  2. Dasgupta, Purnendu K., Yining Liu, and Jason V. Dyke. “Iodine nutrition: iodine content of iodized salt in the United States.” Environmental science & technology 42.4 (2008): 1315-1323.
  3. Diosady, L. L., et al. “Stability of iodine in iodized salt used for correction of iodine-deficiency disorders. II.” Food and Nutrition Bulletin 19.3 (1998): 240-250.
  4. De Groot, Leslie, et al. “Management of thyroid dysfunction during pregnancy and postpartum: An Endocrine Society clinical practice guideline.” The Journal of Clinical Endocrinology & Metabolism 97.8 (2012): 2543-2565.
  5. Sang, Zhongna, et al. “Exploration of the safe upper level of iodine intake in euthyroid Chinese adults: a randomized double-blind trial.” The American journal of clinical nutrition 95.2 (2012): 367-373.
  6. Leung AM, Braverman LE. Consequences of excess iodine. Nature reviews Endocrinology. 2014;10(3):136-142. doi:10.1038/nrendo.2013.251.
  7. Hehemann, Jan-Hendrik, et al. “Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota.” Nature 464.7290 (2010): 908-912.
  8. Sonnenburg, PhD, Justin L. “Microbiology: genetic pot luck.” Nature 464.7290 (2010): 837-838.
  9. Zimmermann, Michael B., et al. “Assessment of iodine status using dried blood spot thyroglobulin: development of reference material and establishment of an international reference range in iodine-sufficient children.” The Journal of Clinical Endocrinology & Metabolism 91.12 (2006): 4881-4887.