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 the other halogens, bromine, chlorine, fluorine and astatine, all of which are toxic, because all the halogens 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
Iodine vs 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.
Dietary iodine also occurs naturally as an iodide, such as potassium iodide or sodium iodide (i.e. as in salt).
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.
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 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|
Can you have too much iodine?
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.
Medications containing 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
|Iodine Containing Medications/Supplements|
(Amiodarone, Cordarone, Pacerone)
(Betadine, Massengil, Povidone)
(Iodoquinol, Yodoxin, Vytone)
|Iodine topical ointments
(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.)|
Testing for iodine deficiency
Iodine deficiency can be tested for in various ways:
a) Skin patch test
Enough iodine tincture (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 test is a reliable test on humans.27
b) 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
c) 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. However, this test is available via Regenerus Laboratories – http://regeneruslabs.com/shop/product/urine-iodine-pre-post-loading-nut4-192?search=iodine
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
d) 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.
Dietary Sources of Iodine
Iodine is found in the following foods 35:
|Food||Portion||Average iodine/portion (mcg) (actual iodine content will vary)|
|Organic cow’s milk||200ml||30-65**|
|Eggs||1 egg (50g)||25|
|Bread||1 slice (36g)||5|
|Fruit and veg||1 portion (80g)||3|
**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 advise 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.
For more in depth information about the thyroid and iodine click here: http://www.ncbi.nlm.nih.gov/books/NBK28/
Check out what people are saying on our online community regarding iodine:
Thyroid UK relies on donations so that we can continue to support and campaign for people with thyroid disease and related disorders. If you have found our information helpful, please do think about donating or becoming a member.
Cerebrospinal fluid – a watery fluid that is continuously produced and absorbed and that flows in the ventricles within the brain and around the surface of the brain and spinal cord
Ciliary – part of the eye, the ciliary body is a circular structure just behind the iris composed of the ciliary muscle and ciliary processes which attach to the lens
Cognition – refers to the process of thinking. It is the identification of knowledge, of understanding it and perceiving it
Compounds – made up of diverse elements or ingredients
Deficiency – a lack of, or shortage of something
Element – any of the primary parts or constituents of a thing
Excreted – to expel from the body
Expressions – something that manifests, represents, reflects, embodies, or symbolizes something else the first clinical expression of a disease
Extracted – to withdraw (as the medicinally active components of a plant or animal tissue) by physical or chemical process also : to treat with a solvent so as to remove a soluble substance
Goitre – a swelling of the neck resulting from enlargement of the thyroid gland
Hypothyroidism – a term used to describe an under-active thyroid gland
Ingested – food, drink or another substance taken into the body by swallowing or absorbing it
Mucus membrane – a lubricating membrane lining an internal surface or an organ, as the alimentary, respiratory, and genitourinary canals
Receptors – a specialised cell or group of nerve endings that responds to things such as hormones
Topically – applied to body surfaces such as the skin
- 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
- Changes in Dietary Iodine Explains Increasing Incidence of Breast Cancer with Distand Involvement in Young Women
J Cancer. 2017; 8(2): 174–177
- Periodic Table
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- Periodic Table
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- Iodine, Iodine metabolism and Iodine deficiency disorders revisited
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New study suggests UK is now iodine-deficient. Press Release. 12 April 2011
- 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
- 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
- Scientific Advisory Committee on Nutrition (SACN) Statement on Iodine and Health, February 2014
- Dr Barry Durrant-Peatfield, MB BS LRCP MRCS; The Great Thyroid Scandal and How to Survive it. Pp 131-135
- Iodine, thyroxine (T4), triiodothyronine (T3), 3,3′,5′-triiodothyronine (rT3), 3,3′-diiodothyronine (T2) in normal human thyroids. Effect of excessive iodine exposure
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- Evolutionary roots of iodine and thyroid hormones in cell-cell signalling
Susan j Crockford
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- 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
- Radio-iodine therapy and Helicobacter pylori infection
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Ann Nucl Med. 2008 Dec;22(10):917-20. doi: 10.1007/s12149-008-0197-1. Epub 2009 Jan 8
- Iodine Nutrition in Pregnancy and Lactation
Angela M. Leung, MD, MSc, Elizabeth N. Pearce, MD, MSc, and Lewis E. Braverman, MD
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- Benefit and harm of iodine in wound care: a systematic review
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- 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
- 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
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- 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
- Contrast Medium: Using Gadolinium or Iodine in Patients with Kidney Problems
Author: Prof Stacy Goergen*
- Adverse Reactions to Contrast Material
Alexander Morzycki, Anuj Bhatia, Kieran J Murphy
Canadian Association of Radiologists Journal: Volume 68, May 2017, 187-193
- Adverse Reactions to Iodinated Contract Media
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- Abraham, G.E., Flechas, J.D., Hakala, J.C., Orthoiodosupplementation: Iodine Sufficiency of the Whole Human Body. The Original Internist, 9:30-41, 2002
- Theodore Zava; Evaluation of the Iodine Loading Test: Urine Iodine Excretion Kinetics after Consumption of 50 mg Iodine/Iodid
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Dated updated: 27/02/20 (V1.1)
Review date: 11/10/20