A century ago, large parts of Switzerland and Central Europe had an endemic iodine problem. In some Swiss Alpine regions, up to 90 percent of schoolchildren showed signs of enlarged thyroid glands, and cretinism – severe, irreversible cognitive and physical impairment caused by iodine deficiency in the womb – was common enough that Napoleon ordered a census of cretins in the Canton Valais in 1800, recording 4’000 among 70’000 inhabitants. In 1922, Switzerland became the first country in the world to introduce iodised table salt. Within a generation, goitre had virtually disappeared, and no new endemic cretins were born after 1930.

That success is now being quietly undone – not through any failure of policy, but through a shift in consumer behavior that few people have noticed, and fewer still connect to their own health. A April 2026 column by Alice Klein in New Scientist put it well: iodised salt has become unfashionable, crowded out in kitchen cupboards by Himalayan pink rock salt, sea salt flakes, fleur de sel, and other specialty products that are widely marketed as healthier but contain no meaningful iodine. At the same time, fish consumption is declining, dairy is increasingly replaced by plant milks, and processed foods – which typically use non-iodised salt – make up an ever-larger share of what people eat.

The consequences are measurable. A 2025 study in The Journal of Nutrition, using NHANES data from 2001 to 2018, found that the proportion of Americans with inadequate iodine intake nearly doubled over that period, with 46 percent of pregnant women now falling short. A January 2026 review published in the Proceedings of the Nutrition Society found that median urinary iodine concentration in UK women of reproductive age is now below the WHO threshold for adequacy. In Australia, despite mandatory iodisation of bread since 2009, research consistently shows that pregnant and breastfeeding women remain at risk – mandatory fortification of bread alone has not been sufficient to meet the higher iodine needs of pregnancy.

What Iodine Actually Does

Iodine is essential for the production of the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine), which regulate metabolism, energy production, body temperature, heart rate, digestion, mood, sleep quality, and cognitive function. The thyroid gland is iodine’s only significant use in the human body – but through its hormone output it influences nearly every system.

The consequences of deficiency follow directly from this central role. Mild to moderate chronic deficiency causes hypothyroidism – an underactive thyroid – with symptoms that are non-specific and easily attributed to other causes: persistent fatigue, unexplained weight gain, cold sensitivity, hair thinning, brain fog, constipation, low mood, and disrupted sleep. Because these symptoms overlap with many other conditions, and because thyroid panels are not always included in routine blood work, iodine deficiency as an underlying driver is frequently missed.

The consequences are most severe during pregnancy and early childhood. Thyroid hormones regulate fetal brain development from the earliest stages – before the fetus has developed its own thyroid function. A meta-analysis of 21 studies by Bleichrodt and Born (1994) estimated that eliminating iodine deficiency raises average IQ by 13.5 points. Research by economists Feyrer, Politi, and Weil (2017), using US military data from before and after salt iodisation in 1924, found that iodisation raised IQ by approximately one standard deviation – equivalent to roughly 15 IQ points – in the quarter of the population most deficient in iodine, and could explain roughly a decade’s worth of the 20th-century rise in IQ in the United States. Politi’s parallel study of Switzerland (2010) found that salt iodisation increased school graduation rates by approximately 10 percent in previously deficient cantons. In children, ongoing deficiency after birth affects brain development, growth, and school performance – with case reports describing children who are short for their age, chronically tired, and academically delayed, where iodine deficiency turned out to be the cause.

In adults, persistent deficiency causes visible goitre in more severe cases – the neck swelling that was common across the Alps before 1922 – and subclinical thyroid underfunction in milder cases that may go undiagnosed for years.

Why Deficiency Is Returning

Three converging trends drive the resurgence.

The specialty salt shift. Iodised table salt has been displaced by products that carry no standardised iodine. Some specialty salts actively market the absence of added iodine as a mark of purity or naturalness – even though iodine is itself a naturally occurring element. What consumers may not realise is that these attractive alternatives contribute nothing to iodine status. The same applies to processed and takeaway foods, which are made with non-iodised salt for processing reasons and now account for a substantial share of daily salt intake in most Western countries.

Reduced fish and dairy consumption. Seafood – historically the most important dietary iodine source alongside dairy – is eaten less frequently, partly due to concerns about mercury contamination and microplastics, and partly through the broader shift toward plant-based eating. Cow’s milk is a meaningful iodine source: iodine is added to cattle feed, and iodine-based disinfectants used in milking further contribute to milk’s iodine content. Replacing dairy with plant milks removes this source entirely, as plant milks are typically not iodine-fortified.

Overcorrection on salt reduction. Decades of public health messaging about reducing salt intake have been absorbed unevenly. Some people – often those who are already health-conscious – have reduced iodised salt intake to a degree that removes a reliable iodine source without being aware that it was serving a specific nutritional function.

Switzerland’s situation is particularly relevant. The concentration of iodine in Swiss table salt has been raised progressively since 1922 – from 3.75 mg/kg at introduction to 25 mg/kg since 2014 – reflecting the ongoing monitoring work of the Swiss Fluoride and Iodine Commission. According to the Commission, iodised salt remains the main iodine source in the Swiss diet, particularly through processed foods such as bread. But as consumers shift to non-iodised specialty salts, this protection weakens – especially for the groups with the highest needs: pregnant women, breastfeeding mothers, and those eating predominantly plant-based diets.

Food Sources and Supplementation

The recommended daily intake for adults is 150 mcg. During pregnancy it rises to 220-250 mcg, and during breastfeeding to 250-290 mcg. The tolerable upper intake level set by most health authorities is 1’100 mcg per day for adults – relevant because both too little and too much iodine cause thyroid dysfunction.

Iodised table salt remains the simplest and most reliable approach for most people. One teaspoon provides roughly 400-500 mcg of iodine – sufficient for daily needs. Returning to iodised salt for everyday cooking, while using specialty salts at the table if preferred, is low-risk and effective for most healthy adults.

Dairy products and eggs are good contributors for those who consume them. A glass of cow’s milk provides roughly 50-100 mcg depending on season and farming practice.

Fish and seafood are excellent sources. White fish such as cod and haddock, as well as shellfish, provide 50-200 mcg per serving depending on species. Smaller species – sardines, anchovies, herring – carry lower contamination risk than larger predatory fish and are among the most iodine-rich foods available.

Seaweed is the most concentrated food-based iodine source, but this is where the most care is needed. Iodine content varies enormously between species. Dulse (Palmaria palmata) is among the more suitable options for occasional use, with a moderate and relatively predictable iodine content of roughly 150-300 mcg per gram. Kelp and kombu can contain 1’500-4’000 mcg per gram and should not be used as routine iodine sources – regular consumption at any meaningful quantity risks exceeding the tolerable upper limit.

Iodine supplements in tablet or drop form are effective for those who cannot achieve adequate intake from diet. For most people who simply return to iodised salt or maintain adequate dairy and fish intake, supplementation is unnecessary. For pregnant women not achieving adequate dietary iodine, a prenatal supplement containing 150 mcg of iodine is recommended by health authorities in many countries – but should be discussed with a doctor or midwife, particularly for women with pre-existing thyroid conditions.

Switzerland – Where Iodised Salt Was Invented

Switzerland’s geological iodine poverty is precisely the reason it led the world in iodised salt. Alpine terrain loses iodine through glaciation and leaching over millennia, leaving locally produced food very low in iodine. In certain regions before 1922, nearly half of all babies had palpable thyroid glands; up to 30 percent of young men were unfit for military service due to goitre. The introduction of iodised salt at 3.75 mg iodine per kilogram of salt transformed the population’s health within a generation.

The Swiss Fluoride and Iodine Commission continues to monitor population iodine status. The Commission has raised the iodine content of table salt progressively over the decades – 7.5 mg/kg in 1962, 15 mg/kg in 1980, 20 mg/kg in 1998, and 25 mg/kg since 2014. Each increase reflected survey data showing insufficient population iodine status. The fact that it has been necessary to raise the dose repeatedly over a century – even with iodised salt in place – illustrates how dependent Switzerland is on this single intervention.

For most people in Switzerland, the practical conclusion is simple: use iodised table salt for everyday cooking. It is the appropriate default for a population living in iodine-poor terrain, and it is available in every supermarket at negligible cost.