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Mysterious medical allstar

You probably know iodine from the charmingly brownish disinfection products that are often used in professional wound dressing. Or maybe you’ve used iodine pills to disinfect water while travelling. At the very least, you’ve likely seen it as the proud proclamation “iodized” on your table salt, or it’s more modern version: “non-iodized”. What you probably haven’t heard before is how many areas of health iodine can influence, and how many people are actually deficient in this easily overlooked nutrient.

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Fig. 1: The good stuff

What does it do?

Your thyroid needs iodine to produce the hormones T3 and T4. These raise body temperature and resting metabolic rate, improve skin regeneration, hair growth and muscle regeneration, and are absolutely necessary for proper physical and mental development of children.

What if I get too little?

The thyroid gland will not function optimally, feelings of fatigue and being cold can result, as well as slow wound healing, hair loss and an enlarged thyroid (goiter).

How much do I need?

Official recommendations range from 100-200 µg per day, with the optimum at 150 µg. About 100 µg are lost via the urine every day and are the bare necessity, 200 µg are used to correct a deficiency or support a pregnancy.

Should I supplement?

That depends on your diet. Iodine is contained in seafood, algae and iodized salt. If you do not consume any of those, supplementing 100-200 µg per day would make sense.

 

Health effects

Traces of magic

The reason why iodine is so popular in disinfection products is because it’s really deadly to bacteria, and can even inactivate viruses.[1] At the same time, it’s comparably skin-friendly,[2] but shouldn’t be used longer than necessary or it can delay wound healing.[3] Because of its antimicrobial talents, iodine is also popular in water disinfection, where it offers a practical but imperfect solution. While the disinfection itself is effective, drinking iodine-enriched water can lead to an overdose of the nutrient.[4]

Nutritionally speaking, iodine is known as a mineral of which we need very little amounts – a so-called essential trace element. Thirty percent of all the iodine we eat is directly shipped to our thyroid gland, where it is used to produce two hormones that sound like magic spells from a fantasy movie: tri-iodo-thyronine (“T3”) and thyroxine (“T4”). And while they probably can’t make you go invisible or able to breathe underwater, these hormones almost magically influence your energy metabolism. By nudging your body to provide energy and directly telling tissues to grow, they regulate skin health, wound healing, muscle regeneration and hair growth. Through their influence on calorie availability, they also increase heart rate, body temperature and resting metabolic rate. For more details see below.

Note: The following list details the effects of optimal levels of iodine and the resulting T3 and T4 status on health under the assumption of a normally functioning thyroid gland.

Energy metabolism

– stimulates fat burning and carbohydrate availability & utilization and so provides energy for day-to-day activity[5]

– increases thermogenesis and thereby raises body temperature[6]

– increases heart rate and resting metabolic rate[5, 7]

– stimulates cholesterol metabolism and thereby lowers cholesterol levels[5]

Cell growth & regeneration

– signals your body to free up energy and then directly stimulates proliferation of all kinds of cells, thereby regulating normal physical development in children, and skin and hair growth in both children and adults[8, 9]

– stimulates wound healing and muscle regeneration[5, 9]

Hormones

– increases sensitivity of many tissues (heart, brown and white fat, liver, hypothalamus) to catecholamines such as adrenaline[5]

– regulates levels of thyroid stimulating hormone (TSH) and thereby influences its own activity according to current thyroid hormone levels[10]

 

Deficiency

Low battery status

According to rough estimations, about two billion people around the world take in too little iodine. This primarily hits less developed countries which do not have iodized salt, but even in Europe up to 50% of all people have sub-optimal levels of iodine. Overall, iodine intakes tend to fall rather than rise in industrialized countries.[11, 12] Because iodine is found mostly in seafood and salt, a health-conscious diet may actually contribute to a deficiency in this micronutrient. As the body’s levels of iodine decrease, the thyroid tends to become overactive (hyperthyroidism) in order to use the remaining iodine more efficiently. While this is an effective strategy, it increases the risk for goiter and possibly thyroid cancer. In cases of severe iodine deficiency, the thyroid tends to become underactive (hypothyroidism), leading to lower levels of the energy regulator hormones T3 and T4. The consequences are especially grievous in children, where they can range from increased infant mortality to impaired physical and mental development.[10] In both children and adults, low T3/T4 levels may whack energy metabolism out of balance, with health consequences such as: frequently feeling fatigued and cold, having flaky skin, hair loss and an enlarged thyroid (goiter). See below for more detail.

Note: The following list details the effects of chronic moderately or severely insufficient levels of iodine and the resulting T3 and T4 status on health under the assumption of a normally functioning thyroid gland.

Energy metabolism

– reduction of available energy can lead to otherwise inexplicable feelings of fatigue[13]

– lack of thermogenesis stimulation can lead to frequently feeling cold[13]

may lead to weight gain through lower energy expenditure, but there is no clear link, as thyroid hormones may help reduce appetite along with the reduced metabolic rate[5]

Cell growth & regeneration

– in children, lack of available energy and tissue growth stimulation can lead to higher infant mortality and impair physical and mental development, which is often irreversible[10]

– lack of skin cell growth stimulation leads to slower skin regeneration, slowing wound healing and resulting in flaky skin[9]

– lack of hair follicle growth stimulation may lead to hair loss[9]

– imbalanced muscle energy metabolism slows down muscle regeneration[5]

Hormones

– low levels of T3 and T4 lead to increase of thyroid stimulating hormone (TSH), of which chronically high levels can cause thyroid enlargement (goiter) and possibly thyroid cancer[10, 11]

– lack of thyroid hormones negatively affects hormones responsible for the menstrual cycles, which can result in heavier and/or more frequent periods[14]

 

Dosage

Mining the mineral

The daily requirements of iodine were studied by looking at how much iodine leaves the body every day via the urine, then combining that with the knowledge at which levels unwanted side effects start to appear. Because the body eliminates between 40-100 µg of iodine per day, about 100 µg per day is the minimum recommended intake. A bonus of around 50 µg on top of that is supposed to give extra certainty in optimizing the levels.[15] Below is a table taken from the NIH.[16]

Iodine requirements as recommended by the NIH. One microgram (µg / mcg) is a thousandth of a milligram (mg).

Life Stage

Recommended Amount

Birth to 6 months

110 mcg

Infants 7–12 months

130 mcg

Children 1–8 years

90 mcg

Children 9–13 years

120 mcg

Teens 14–18 years

150 mcg

Adults

150 mcg

Pregnant teens and women

220 mcg

Breastfeeding teens and women

290 mcg

Recommended daily amounts are higher for pregnant and breastfeeding women. This is for two reasons: first, because pregnant and lactating women have increased needs, second, because iodine deficiencies during these times have severe consequences and should be avoided with absolute certainty.[17, 18] The maximum intake for adults should not exceed either 500 µg or 1000 µg per day,[16, 19] depending on your personal iodine history and thyroid status. Thyroids that are overactive and enlarged from a long-term moderate iodine deficiency will react more strongly to sudden large or even just adequate doses, which can have similar consequences to iodine deficiency. Assuming an adequate dose of around 150 µg per day, over time the thyroid status will normalize even after long-term deficiency.[15]

 

Supplementation

Power of the sea

Having proper iodine levels sounds really great. The problem lies in actually getting the stuff. You can barely find iodine in produce, because most soils are iodine-starved – the micronutrient has been “washed” out of the ground by many millennia worth of rain. In most of the developed countries, iodine is added to table salt, which has worked incredibly well to get rid of iodine deficiencies in the population.[20] But nowadays we have a large number of non-iodized salt products, which in a cruel twist of fate are actually marketed as health-conscious. Thanks to that, it’s not a given anymore that we have proper iodine levels, even if we eat a lot of salt. Thankfully, we can find iodine in a variety of foods which we can strategically add to our diet to keep our iodine levels in check (see below).[21-23]

Omnivore

Fish and shellfish (50-100 µg per 100 g/3.5 oz)

Vegetarian

Yoghurt (50 µg per 100 g/3.5 oz, only in the US, in other countries: 10 µg, up to 100 µg)

Milk (30 µg per 100 ml/3.5 oz, only in the US, in other countries: 10 µg, up to 100 µg)

(milk and milk products can contain variable amounts of iodine, due to supplemented animal feed and/or iodine-based disinfectants of cow’s udders)

Vegan

Iodized salt (1,700-7,700 µg per 100 g/3.5 oz, depending on the brand)

Algae:

Kombu/kelp (500-11,000 µg per 100 g/3.5 oz)

Arame (586-5,640 µg per 100 g/3.5 oz)

Hijiki (95-430 µg per 100 g/3.5 oz)

Dulse (40-550 µg per 100 g/3.5 oz)

Wakame (60-350 µg per 100 g/3.5 oz)

Sea lettuce (50-240 µg per 100 g/3.5 oz)

Lithothamnium (30-60 µg per 100 g/3.5 oz)

Nori (5-550 µg per 100 g/3.5 oz)

Algae are a bit problematic because of their sporadically very high iodine content. Especially if you are suffering from a deficiency, you should not take in too much iodine at once. If you want to balance your iodine levels using algae, definitely check the label for the content. Even then, it would be safest to use those on the lower part of the spectrum. Sea lettuce and dulse seem to be the most reliable choices. Kombu, which can be extremely high in iodine, should definitely be soaked before use (see FAQ).

In conclusion, if you regularly eat iodine-rich foods and/or strictly use iodized salt, it’s unlikely that you have a deficiency. But if you avoid seafood and algae and use very little salt in your cooking, a deficiency is quite possible. In this case, supplementation of between 100-200 µg iodine per day can make sense. Supplements based on algae should be avoided because of a high variability of actual iodine content.[24]

 

Frequently asked questions (FAQ)

Because kombu can contain up to 11 mg (that’s 11,000 µg) iodine per 100 g/3.5 oz, using even small amounts to cook can lead to an iodine overdose. A simple fix for this has been invented several hundred years ago, or possibly even earlier: soaking. In a study,[25] soaking algae in water led to a rapid decrease of iodine content of the algae material. Namely, 5 g dry algae were soaked in 500 ml deionized/distilled cool water for up to 24 hours under constant stirring. After only one hour, 60% or more of the iodine had left the algae material. Subsequent boiling reduced the amount even more, but still left a considerable part of the iodine in the algae material. In conclusion, soaking high-iodine algae in cold water (at least 100 ml water per 1 g of algae) for an hour or longer, stirring occasionally, can reduce the iodine content to an amount that is safe for your health. To be extra safe, you can even boil them afterwards in the same amount of (fresh) water for 20 min.

Broken nuclear reactors leak radioactive iodine into the environment.[26] By taking high amounts of iodine via pills, you can ensure that your thyroid primarily uses the non-radioactive version, while excreting most of the radioactive iodine.[11] It’s not a perfect solution, but much better than nothing.

 

Sources

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  2. Kulkarni, A.P. and R.M. Awode, A prospective randomised trial to compare the efficacy of povidone-iodine 10% and chlorhexidine 2% for skin disinfection. Indian Journal of Anaesthesia, 2013. 57(3): p. 270.
  3. Balin, A.K. and L. Pratt, Dilute povidone‐iodine solutions inhibit human skin fibroblast growth. Dermatologic surgery, 2002. 28(3): p. 210-214.
  4. Backer, H. and J. Hollowell, Use of iodine for water disinfection: iodine toxicity and maximum recommended dose. Environmental Health Perspectives, 2000. 108(8): p. 679-684.
  5. Mullur, R., Y.-Y. Liu, and G.A. Brent, Thyroid hormone regulation of metabolism. Physiological reviews, 2014. 94(2): p. 355-382.
  6. Silva, J.E., The thermogenic effect of thyroid hormone and its clinical implications. Annals of internal medicine, 2003. 139(3): p. 205-213.
  7. Klein, I. and K. Ojamaa, Thyroid hormone and the cardiovascular system. New England Journal of Medicine, 2001. 344(7): p. 501-509.
  8. Oetting, A. and P.M. Yen, New insights into thyroid hormone action. Best practice & research Clinical endocrinology & metabolism, 2007. 21(2): p. 193-208.
  9. Safer, J.D., Thyroid hormone action on skin. Dermato-endocrinology, 2011. 3(3): p. 211-215.
  10. Zimmermann, M.B. and K. Boelaert, Iodine deficiency and thyroid disorders. The Lancet Diabetes & Endocrinology, 2015. 3(4): p. 286-295.
  11. Zimmermann, M.B., Iodine deficiency. Endocrine reviews, 2009. 30(4): p. 376-408.
  12. Zimmermann, M.B., P.L. Jooste, and C.S. Pandav, Iodine-deficiency disorders. The Lancet, 2008. 372(9645): p. 1251-1262.
  13. Kostoglou-Athanassiou, I. and K. Ntalles, Hypothyroidism-new aspects of an old disease. Hippokratia, 2010. 14(2): p. 82.
  14. Zagrodzki, P., R. Ratajczak, and R. Wietecha-Posłuszny, The interaction between selenium status, sex hormones, and thyroid metabolism in adolescent girls in the luteal phase of their menstrual cycle. Biological trace element research, 2007. 120(1-3): p. 51-60.
  15. Zimmermann, M.B., Iodine requirements and the risks and benefits of correcting iodine deficiency in populations. Journal of Trace Elements in Medicine and Biology, 2008. 22(2): p. 81-92.
  16. Micronutrients, I.o.M.U.P.o., Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001. 8, Iodine. Available from: https://www.ncbi.nlm.nih.gov/books/NBK222323/. 2001.
  17. Secretariat, W., et al., Prevention and control of iodine deficiency in pregnant and lactating women and in children less than 2-years-old: conclusions and recommendations of the Technical Consultation. Public health nutrition, 2007. 10(12A): p. 1606-1611.
  18. Glinoer, D., Pregnancy and iodine. Thyroid, 2001. 11(5): p. 471-481.
  19. Scientific Committee on Food, S.P.o.D.P., Nutrition and Allergies, Tolerable Upper Intake Levels for Vitamins and Minerals. www.efsa.europa.eu, © European Food Safety Authority, 2006.
  20. Weng, H.-X., et al., Increment of iodine content in vegetable plants by applying iodized fertilizer and the residual characteristics of iodine in soil. Biological trace element research, 2008. 123(1-3): p. 218-228.
  21. Dahl, L., et al., The iodine content of Norwegian foods and diets. Public health nutrition, 2004. 7(4): p. 569-576.
  22. Dahl, L., et al., Iodine concentration in Norwegian milk and dairy products. British Journal of Nutrition, 2003. 90(3): p. 679-685.
  23. Jahreis, G., M. Leiterer, and A. Fechner, Jodmangelprophylaxe durch richtige Ernährung. Prävention und Gesundheitsförderung, 2007. 2(3): p. 179-184.
  24. Zimmermann, M. and F. Delange, Iodine supplementation of pregnant women in Europe: a review and recommendations. European journal of clinical nutrition, 2004. 58(7): p. 979-984.
  25. Nitschke, U. and D.B. Stengel, Quantification of iodine loss in edible Irish seaweeds during processing. Journal of Applied Phycology, 2016. 28(6): p. 3527-3533.
  26. Taghipour, F. and G.J. Evans, Iodine behavior under conditions relating to nuclear reactor accidents. Nuclear technology, 2002. 137(3): p. 181-193.