Knowing that today iodine comes either from fish products or (artificially) enriched table salt, how did people who lived far from the sea survive before (especially during the the Middle Ages)?

Edit 1: nowadays we could find some iodine in cow milk, cheese and eggs but those sources are artificial

(Increased iodine content in food due to greater use in: food processing, animal rations, antimicrobial agents...)


Edit 2

A small amount of iodine enters the atmosphere and, through rain, enters ground water and soil near the sea


Summarized of the comments: thanks to ddiez this question has been partially answered. But as vsz pointed out the the mystery remains:

areas with iodine deficiency didn't get completely depopulated during the Middle Ages seems to suggest that it does not affect all people that severely.

So the question remains: could humans survive and reproduce without any iodine source?

Edit 3:

“If all women in the UK took iodine supplements while pregnant, IQ would rise by 1.2 points per child” but some says "Some observational studies suggest supplements could even lower IQ, perhaps because excess iodine might harm the thyroid gland." (Newscientist, August 2015)

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    $\begingroup$ They had problems - strumae were pretty common in old ages. $\endgroup$
    – Chris
    Oct 8, 2014 at 12:16
  • $\begingroup$ @Chris, I would like to suggest tagging this question with "iodine" and/or maybe "thyroid hormones". None currently exist. No experience so far with tagging and its rules. $\endgroup$
    – ddiez
    Oct 8, 2014 at 12:45
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    $\begingroup$ @ddiez I think iodine is a bit too specific to warrant a tag and thyroid hormones as a tag only indirectly describes this question; I think it's prefectly appropriately tagged $\endgroup$
    – Armatus
    Oct 8, 2014 at 13:13
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    $\begingroup$ @Armatus I understand, and agree, with your arguments. Thanks for the explanation. $\endgroup$
    – ddiez
    Oct 8, 2014 at 13:47
  • $\begingroup$ @GuillaumeCombot, I am afraid you have misunderstood my answer/comments. Iodine appears naturally in food (although certainly can be added). Iodine deficiency has not been an issue at all in the Middle Ages in places where the water or soil was iodine-rich. Iodine deficiency is still an issue today in many parts of the world. I have updated my answer to make things more clear. $\endgroup$
    – ddiez
    Oct 9, 2014 at 16:21

1 Answer 1


Iodine is naturally found in sea water and soil but it is not evenly distributed, with many areas in the world with low levels of iodine. Iodine accumulates naturally in fish, and plants growing in iodine-rich soil. Mammals that eat these plants get iodine from them, which then accumulates in the milk, making dairy and its products (e.g. cheese) another natural source of iodine. Table 1 from the Iodine deficiency section at the American Thyroid Association web page contains a brief list of iodine-rich food.

Quoting the web site:

What are the sources of iodine?

Iodine is present naturally in soil and seawater. The availability of iodine in foods differs in various regions of the world. Individuals in the United States can maintain adequate iodine in their diet by using iodized table salt (unless they have to restrict the amount of salt in their diet), by eating foods high in iodine, particularly dairy products, seafood, meat, some breads, and eggs, and by taking a multivitamin containing iodine (see below). However, the amount of iodine in foods is not listed on food packaging in the U.S., and it can be difficult to identify sources of iodine in foods.

As mentioned, the amount of iodine in some food depends on how much iodine is present in the water or soil. For example, in the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) there is some mention about the natural sources of iodine and its limitations:

Most of the iodine we consume comes from what we eat and drink. Seafood is usually a good source because the ocean contains considerable iodine. Freshwater fish reflect the iodine content of the water where they swim, which may be deficient. Other foods vary tremendously in iodine content, depending on their source and what may have been added. Plants grown in iodine-deficient soil do not have much iodine, nor do meat or other products from animals fed on iodine-deficient plants. Because the breast concentrates iodine, dairy products are usually a good source, but only if the cows get enough iodine.

Iodine deficiency causes important health problems. Iodine is necessary to produce thyroid hormones. Lack of thyroid hormones causes hypothyroidism, cretinism and goiter. However, iodine deficiency is not mortal per se.


As a consequence, in the Middle Ages iodine deficiency was not an issue in places where water and/or soil was rich in iodine. In other places they would suffer of iodine deficiency, leading to a higher impact of the related diseases.

Nowadays, iodine is added artificially to food in order to prevent iodine deficiency. This practice has diminished the impact of iodine deficiency-related diseases. However, iodine deficiency is still an important issue today, as reported by the World Health Organization in its map describing the Degree of Public Health Significance of Iodine Nutrition. As shown in the map, in many places in the world there is still risk of severe iodine deficiency.

WHO - Degree of Public Health Significance of Iodine Nutrition


  1. Iodine deficiency - Wikipedia
  2. American Thyroid Association
  3. World Health Organization
  4. International Council for the Control of Iodine Deficiency Disorders (ICCIDD)
  • $\begingroup$ thank for your detailed response! I added more details in my question, it's more tricky that it sound. $\endgroup$
    – JinSnow
    Oct 8, 2014 at 13:30
  • $\begingroup$ @GuillaumeCombot I am sorry but cannot see how your edits change my answer. Is your question different? Basically in the Middle Ages people got iodine from food, wether it be sea food or other food (e.g. vegetables and dairy) from places with iodine rich soil. Iodine deficiency does not typically cause death - but some (very serious though) diseases. During the Middle Ages those diseases were more prevalent. $\endgroup$
    – ddiez
    Oct 8, 2014 at 13:53
  • $\begingroup$ I suppose they could have eaten thyroids, that's where the most iodine would have been. But most people at that time probably couldn't get much meat anyway, and they probably wouldn't know enough to associate thyroid consumption with preventing iodine deficiency, or even knew about iodine deficiency. And I have no evidence to say whether or not anyone actually ever ate thyroid. $\endgroup$
    – user137
    Oct 8, 2014 at 14:26
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    $\begingroup$ @user137 certainly in the Middle Ages they did not know about iodine deficiency and eating thyroids would, very likely, not be extended. Iodine deficiency appeared in places with iodine deficiency in soil or water, or (and that is a fair comment) in places where people didn't have access to food or water. However in those places starvation and malnutrition would probably be a much more serious issue than iodine deficiency. $\endgroup$
    – ddiez
    Oct 8, 2014 at 14:31
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    $\begingroup$ The fact that those areas with iodine deficiency didn't got completely depopulated during the Middle Ages seems to suggest that it does not affect all people that severely. Are there people who can have good health with much less iodine that can cause others to suffer severe symptoms? $\endgroup$
    – vsz
    Oct 8, 2014 at 18:24

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