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Radioactive Iodine Treatment

The thyroid uses iodine as its main raw material and so this radioactive form concentrates in the colloid (hormone forming) tissue in the thyroid gland.

I 131 concentrates in the cells and its radioactivity destroys them.  Depending on how much is given initially depends of course on the severity of cellular damage.  The amount given is calculated by body weight and the presumed severity of the over-activity of the thyroid forming cells.

There are three possible scenarios.  One is that the calculation was right.  The amount of thyroid tissue left is just right to produce the right level of hormones in the bloodstream.  Of course, the cells may later partly recover, and then it may have to be done all over again or further damage and loss of function may occur and the thyroid as a whole may become underactive.

The second scenario is that the patient continues to have an overactive thyroid in spite of treatment, and a further dose of radioactive iodine – or doses – may have to be given at once.

The third scenario is a good deal more common.  Overkill becomes evident in a few days, and thyroid hormone in the bloodstream falls pretty quickly.  Very soon thyroid replacement (usually thyroxine) becomes necessary.

What is iodine?

Iodine, a relatively rare element, is a member of a class of chemical elements known as halogens and has many important roles in the body. However, it can be crowded out by other toxic halogens which compete with each other for receptor and binding sites in the body.1,2 The other halogens are:3


      • Bromine – used in agriculture, sanitation and fire retardants as well as an alternative to chlorine in swimming pools

      • Chlorine – used in swimming pools

      • Fluorine – in water as fluoride; found in soil

      • Astatine – radioactive chemical element 4

    What’s the difference between iodine and iodide?

    Some people get confused about iodine and iodide. Iodide is the state of iodine when it bonds with another element, such as potassium. In this form, iodine can be ingested or applied topically.

    Iodine and iodide are actually different expressions of the same element. Iodides represent a safe form of iodine for ingestion.5  When you purchase iodine from the local drug store, it’s usually an iodide solution. This combination allows the body to absorb and use it safely. Dietary iodine also occurs naturally as an iodide, such as potassium iodide or sodium iodide (i.e. as in salt).

    Where is iodine found?

    Iodine-containing compounds are extracted from the ashes of burnt seaweed and found in salty oil well brines, Chilean saltpetre, seawater and solid rocks that form when seawater evaporates.  Seaweed concentrates large amounts of iodine from ocean water and it is also found in some types of soil.6             

    Why do we need it?

    Iodide plays an important role in regulating the activity of the thyroid gland. It is found in every cell of the body and is stored in particularly high concentrations in the thyroid gland, whilst large amounts are also stored in the salivary glands, the cerebrospinal fluid, the brain, the mucus membrane layer of the stomach, the choroid plexus (four sets of branching vessels in the brain where cerebrospinal fluid is produced), the breasts, the ovaries, and the ciliary body of the eye.7

    Iodine deficiency is associated with goitre and hypothyroidism; in England, this is sometimes known as Derbyshire Neck.  Babies born with severe thyroid function deficiency which is left untreated for several months may be at risk of growth failure – thyroid hormones influence growth from birth up to age 20 – and permanent mental retardation (cretinism).8

    The Society for Endocrinology stated:

    “Young women of child-bearing age are the most susceptible to the adverse effects of iodine-deficiency and even mild deficiency may have an impact on the developing brain of foetuses and young children. It can also cause goitre. According to the World Health Organisation, iodine-deficient communities have IQs up to 13.5 points lower than similar but iodine-sufficient communities.” 9

    A 2011 study of the iodine status of 14 to 15-year-old school girls in the UK concluded that the UK, like Australia and the USA, is now iodine-deficient.10,11  Young women of childbearing age are the group most susceptible to the adverse effects of iodine deficiency. Nearly 70% of the samples were below 100ug/L and 18% of samples showed very low iodine levels below 50μg/L. The researchers considered this finding to be of huge public health importance since mild iodine deficiency impairs cognition in children and severe iodine deficiency reduces IQ by 10 to 15 points.

    Dr Mark Vanderpump, one of the authors of the research article on iodine states, ‘One cup of milk contains about half the amount of iodine needed per day. A possible explanation for our findings may be that teenage girls are drinking less milk and are less likely to have milk and cereal for breakfast. The solution could be to add iodine to the salt used in products such as bread as has been done in for example Denmark.’ The same could be said of young children who are not now given free milk at school and adults, who think that drinking milk is fattening.

    In response to the Lancet article, the Department of Health’s Scientific Advisory Committee on Nutrition asked for a review of the current evidence10 that some degree of iodine deficiency might affect some groups within the UK population.  They agreed that “the issue of iodine intakes is of considerable public health significance, although the Committee is cautious in drawing conclusions on current evidence due to the limitations of the available data,”12

    Iodine has a number of roles to play in the body13,14


        • it is essential for the production of thyroid hormones15

        • iodine mitochondrion-mediated apoptosis (programmed cell death)16

        • iodine, together with thyroid hormones, has a monitoring and surveillance role, finding and destroying abnormal cells (like pre-cancer cells). Iodine also has an antioxidant and an anti-free-radical action16

        • iodine has a protective and preventative effect against helicobacter pylori, the bacterium that lives in the stomach and causes ulcers and stomach cancer17

        • iodine is needed during pregnancy and lactation for the health of the baby18

        • iodine is a powerful antiseptic and may be used in complete safety – it works even in high dilutions19

      How much iodine do people need?

      The World Health Organisation, The United Nations Children’s Fund (UNICEF), and the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) give the following recommended daily intake of iodine.20

      Life stage Iodine RDI (mcg)*
      Preschool children (0-59 months) 90 µg
      Schoolchildren (6 to 12 years) 120  µg
      Adults (above 12 years) 150 µg
      Pregnant and lactating women. 250 µg
      Table of recommended daily intake of iodine

      Can you have too much iodine?

      For some people, iodine or iodine-containing products may worsen autoimmune thyroid problems such as Hashimoto’s and Graves’ disease, and cause enlargement of the thyroid (goitre).21  On the other hand, some healthcare professionals believe that a high iodine intake, such as seen in Japanese women, can largely prevent breast cancer.2

      If you are thinking of taking iodine supplements, consider having your levels measured to see if you have an actual deficiency.  Once you start supplementing, watch out for any symptoms that develop.

      What medications contain iodine?

      You need to look carefully at any medications you take as iodine is found in a number of these.

      Also, studies have shown that exposure to iodinated contrast media used for X-ray investigations such as angiograms, CT scans and MRI scans is associated with the subsequent development of thyroid disease. 22,23

      Be aware, too, that some people have adverse reactions to iodine.24,25,26

      Anti-arrythmic drugs Amiodarone, Cordarone, Pacerone
      Medicated douches Betadine,  Massengil, Povidone
      Antiparasitics Iodoquinol, Yodoxin, Vytone
      Iodine topical ointments Povidone, Betadine
      X-ray dyes CT scans, intravenous pyelogram (IVP), arteriograms, angiograms, myelograms
      Intravenous pyelograms (IVP’s) radiological procedure used to visualize abnormalities of the urinary system, including the kidneys, ureters, and bladder.
      Potassium iodine Lugol’s solution
      Potassium Iodide  
      Kelp Seaweed
      Table of medications and supplements that contain iodine

      How is iodine deficiency tested?

      Iodine deficiency can be tested for in various ways:

      Skin patch test

      Enough iodine tincture (a mixture of iodine and potassium iodide) is placed on a cotton ball to paint a two-inch circle in a soft place of your body such as your inner thigh or upper arm.  If the painted area has disappeared after an hour, your body is seriously deficient in iodine.  If the painted area is still there after four hours, your body is not deficient in iodine. However, there is no evidence that this is a reliable test on humans.27

      Urine test

      A urine iodine test is most often used in research studies looking into iodine deficiency and is accepted as a good marker of very recent dietary iodine intake20 although there are some controversies over this test.28

      Nutritional supplements and medication may affect the result (they may contain iodine) so you should check with your doctor whether they should be discontinued before the test.  Non-essential supplements should be discontinued 48 hours before the test.

      It is also essential that you don’t drink an excessive amount of fluids for 24 hours before the test as this may affect the result.29

      Iodine loading test

      In an iodine loading test, iodine sufficiency is determined by comparing the amount of Iodine taken to the amount excreted in the urine.30  After ingesting a specified oral dose of iodine, urine is collected for 24 hours and iodide levels are then measured. Because taking iodine is not good for certain people, you should always discuss having this test with your healthcare practitioner.

      If the body has sufficient iodine, most of the ingested iodine will be excreted in the urine.  The more deficient in iodine the body is, the less iodine will be excreted in the urine. Whole body iodine sufficiency is reached when 90% or more of the ingested amount is excreted in the urine.

      The 24 Hour iodine loading test is not available on the NHS in the UK but is available via Regenerus Laboratories. However, there is some evidence that this test does not provide a realistic assessment of an individual’s whole body iodine sufficiency or deficiency due to flaws in the methodology and the use of an arbitrary excretion cut-off point.31,32

      Blood test

      Iodine levels can also be measured by means of a blood test. However, some doctors feel that this isn’t as good as a urinary test 33 and urine testing seems to be the favoured test for research. If your doctor is unable to do an iodine blood test, you can obtain this from Medichecks.

      Will my doctor do an iodine test?

      It is quite likely that your NHS GP will not do a test because the Department of Health advisers state that you should be able to get all the iodine you need by eating a varied and balanced diet.34

      What if I am deficient?

      If your doctor has confirmed that you are deficient, there are several options but you do need to be careful because too much supplementation can cause problems. You could try increasing your iodine levels by eating foods that contain iodine before you try supplementation.

      What are the dietary sources of iodine?

      Iodine is found in the following foods 35:

      Food Portion Average iodine/portion (mcg) (actual iodine content will vary)
      Cow’s milk 200ml 50-80**
      Organic cow’s milk 200ml 30-65**
      Yoghurt 150g 50-100**
      Eggs 1 egg (50g) 25
      Cheese 40g 15
      Haddock 120g 390
      Cod 120g 230
      Place 130g 30
      Salmon Fillet 100g 14
      Canned Tuna 100g 12
      Prawns 60g 6
      Scampi 170g 160
      Meat 100g 10
      Poultry 100g 10
      Nuts 25g 5
      Bread 1 slice (36g) 5
      Fruit and veg 1 portion (80g) 3
      Table of dietary sources of iodine

      **Depending on the season, higher value in winter

      It’s also found in iodized salt, sea salt, seaweed, kelp, foods that contain carrageen, agar-agar, algin or alginate, many prepared and/or cured meats (ham, bacon, sausage, corned beef), dried fruit, margarine, canned vegetables, commercial bakery products, chocolate, molasses, soy products, any vitamins or supplements that contain iodine, FD&C red dye #3, cereals – wheat etc, (depending on how much iodine was in the soil where they were grown).

      However, if this is not possible for you to eat these foods or you remain deficient there are iodine supplements available:


          • kelp tablets (seaweed) – available from most health shops

          • iodized salt – available from some supermarkets

          • potassium iodide tablets – available only on prescription

          • Lugol’s iodine – a solution of elemental iodine and potassium iodide in water used on the skin as an antiseptic – can be toxic if too much is taken

          • nascent Iodine – iodine in an atomic form rather than a molecular form and supposedly more bioavailable – no research articles could be found on this product

        The Department of Health advises that “you should be able to get all the iodine you need by eating a varied and balanced diet. If you take iodine supplements, don’t take too much as this could be harmful. Taking 0.5mg or less a day of iodine supplements is unlikely to cause any harm.”

        There is a lot of controversy over the use of iodine.36  You need to research well before you consider which action to take. Talk to your doctor if you are not sure what dosage to take for deficiency.

        Read more in-depth information about the thyroid and iodine.

        For more support check out our online community:

        Dated updated: 16/04/2021 (V1.3) Review date: 11/10/21



            1. Galletti, P: Effect of fluorine on thyroidal iodine metabolism in hyperthyroidism. The Journal of Clinical Endocrinology & Metabolism October 1, 1958 vol. 18 no. doi: 10.1210/jcem-18-10-1102

            1. Changes in Dietary Iodine Explains Increasing Incidence of Breast Cancer with Distand Involvement in Young Women
              Jay Rappaport
              J Cancer. 2017; 8(2): 174–177

            1. Periodic Table
              Royal Society of Chemistry

            1. Periodic Table
              Royal Society of Chemistry

            1. What is the difference in iodine and iodide?

            1. Extracting iodine from seaweed
              Royal Society of Chemistry

            1. Iodine, Iodine metabolism and Iodine deficiency disorders revisited
              Farhana Ahad and Shaiq A Ganie
              Indian Journal of Endocrinology and Metabolism

            1. Goiter
              American Thyroid Association

            1. Society for Endocrinology
              New study suggests UK is now iodine-deficient. Press Release. 12 April 2011

            1. Vanderpump PJ; Lazerus J H, Smyth P P, Laurburgh P; Et Al; Iodine Status of UK Schoolgirls: a Cross Sectional Survey, The Lancet, Volume 377, Issue 9782, Pages 2007 – 2012, 11 June 2011

            1. Vanderpump M Lazarus J Smyth P Burns R Eggo M Han, T et al. Assessment of the UK iodine status: a national survey. Endocrine Abstracts. Presented at the Society for Endocrinology BES 2011: 11 April 2011-14 April 2011

            1. Scientific Advisory Committee on Nutrition (SACN) Statement on Iodine and Health, February 2014

            1. Dr Barry Durrant-Peatfield, MB BS LRCP MRCS; The Great Thyroid Scandal and How to Survive it. Pp 131-135

            1. Iodine, thyroxine (T4), triiodothyronine (T3), 3,3′,5′-triiodothyronine (rT3), 3,3′-diiodothyronine (T2) in normal human thyroids. Effect of excessive iodine exposure
              Reinwein D, Durrer HA, Meinhold H.
              Horm Metab Res. 1981 Aug;13(8):456-9

            1. Evolutionary roots of iodine and thyroid hormones in cell-cell signalling
              Susan j Crockford
              Department of Anthropology, PO Box 3050 STN CSC, University of Victoria, British Columbia, Canada V8W 3P5

            1. The Extrathyronine Actions of Iodine as Antioxidant, Apoptotic and Differentiation Factor in Various tissues
              Carmen Aceves, Brenda Anguiano, and Guadalupe Delgado
              Thyroid. 2013 Aug; 23(8): 938–946

            1. Radio-iodine therapy and Helicobacter pylori infection
              Gholamrezanezhad A1, Mirpour S, Saghari M, Abdollahzadeh J, Pourmoslemi A, Yarmand S.
              Ann Nucl Med. 2008 Dec;22(10):917-20. doi: 10.1007/s12149-008-0197-1. Epub 2009 Jan 8

            1. Iodine Nutrition in Pregnancy and Lactation
              Angela M. Leung, MD, MSc, Elizabeth N. Pearce, MD, MSc, and Lewis E. Braverman, MD
              Endocrinol Metab Clin North Am. 2011 Dec; 40(4): 765–777.

            1. Benefit and harm of iodine in wound care: a systematic review
              Vermeulen H1, Westerbos SJ, Ubbink DT.
              J Hosp Infect. 2010 Nov;76(3):191-9

            1. 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

            1. A Review: Radiographic Iodinated Contrast Mediia-Induced Thyroid Dysfunction
              Sun Y Lee; Connie M Rhee; Angela M Leung; Lewis E Braverman; Gregory A Brent; Elizabeth N Pearce
              The Journal of Clinical Endocrinology & Metabolism, Volume 100, Issue 2, 1 February 2015

            1. Association Between Iodinated Contrast Media Exposure and Incident Hyperthyroidism and Hypothyroidism
              Connie M. Rhee, MD; Ishir Bhan, MD, MPH; Erik K. Alexander, MD; Steven M. Brunelli, MD, MSCE , Arch Intern Med. 2012;172(2):153-159. doi:10.1001/archinternmed.2011.677

            1. Contrast Medium: Using Gadolinium or Iodine in Patients with Kidney Problems
              Author: Prof Stacy Goergen*
              Inside Radiology

            1. Adverse Reactions to Contrast Material
              Alexander Morzycki, Anuj Bhatia, Kieran J Murphy
              Canadian Association of Radiologists Journal: Volume 68, May 2017, 187-193

            1. Adverse Reactions to Iodinated Contract Media
              Wendy Bottinor, Pritam Polkampally, Ion Jovin
              International Journal of Angiology

            1. Adverse reactions to iodinated contrast media
              Morcos SK, Thomas HS
              Eur Radiol 2001;11(7):1267-75

            1. The Bioavailability of Iodine Applied to the Skin
              Guy E. Abraham, MD

            1. Controversies in urinary iodine determinations
              Offie Porat Soldin
              Clin Biochem. 2002 Nov; 35(8): 575–579

            1. Genova Diagnostics Patient Instruction Leaflet

            1. Iodine Loading Test, Optimox

            1. Abraham, G.E., Flechas, J.D., Hakala, J.C., Orthoiodosupplementation: Iodine Sufficiency of the Whole Human Body. The Original Internist, 9:30-41, 2002

            1. Theodore Zava; Evaluation of the Iodine Loading Test: Urine Iodine Excretion Kinetics after Consumption of 50 mg Iodine/Iodid

            1. Comparing 4 Different Methods Of Iodine Testing
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            1. SACN STATEMENT ON IODINE AND HEALTH – February 2014
              Page 21 (123)

            1. Association of UK Dietitian’s Fact Sheet on Iodine https

            1. Validation of the Orthoiodosupplementation Program: A Rebuttal of Dr. Gaby’s Editorial on Iodine
              Guy E. Abraham, MDand David Brownstein, MD

          Dated updated: 25/08/2021 (V1.4)
          Review date: 11/10/21

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