Without iodine, the thyroid gland cannot produce hormones that enable the human body and the brain to develop properly. The visible consequences of iodine deficiency, such as goitres (swellings in the neck), are bad enough. The invisible ones are much worse: it can cause a 15-point drop in IQ.
Such afflictions were once common. A century ago, one in three schoolchildren in Michigan had a visible neck swelling; in Britain goitres were so endemic in some places that the condition was known as Derbyshire neck. Then manufacturers started fortifying certain foods with iodine, dramatically reducing the scourge. The number of countries where iodine levels are insufficient fell from 113 in 1990 to 21 in 2020.
However, levels in rich countries are slipping. In America, where good data exist, the median urinary concentration of it in adults has fallen from around 300 micrograms per litre in the 1970s to 116 in 2020, just shy of insufficiency, which begins below 100. Most at risk are pregnant women, who need more iodine to keep themselves and their fetuses healthy.
One reason is that diets are changing. Many people get their daily iodine from salt, which has been artificially iodised in America and parts of Europe for a century. But iodisation is often voluntary and inconsistent. Whereas table salt is often fortified, the salt in processed foods generally is not. Gourmet alternatives, from pink to Himalayan, are similarly deficient.
The rise in veganism and climate-conscious eating has also reduced appetites for fish and meat, which are natural sources of iodine. Because dairy farmers add iodine to feedstocks to keep their cattle healthy, milk products are also serendipitously fortified (in Britain and America, a litre of milk contains more iodine than a teaspoon of iodised salt). Alternative milks, which are increasingly popular, mostly lack these protections.
There are simple remedies governments can apply. First, identify the foodstuffs most commonly consumed by the needy population and mandate their iodisation. dairy alternatives and salts used in processed foods should top the list. Iodised salt can be added to bread, as in Australia and Denmark. Large food companies could seize the opportunity to improve their customers’ health before being legally obliged to do so.
Iodine supplements could also be made more widely available, especially to pregnant women; two-fifths of prenatal vitamins in America currently lack the mineral. And public-health messaging on their value should be clearer. In regions where iodine levels in the soil are low, farmers should be incentivised to add more to animal feed.
Such interventions would pay for themselves many times over. Between 1993 and 2019 salt-iodisation schemes are estimated to have prevented 720m cases of deficiency worldwide, with improvements to cognitive development and earning power leading to a net economic benefit of $32bn a year. Poorer countries, where most of the 2bn people with iodine deficiency are thought to live, would have the most to gain.
Some worry that people may be confused if told both to eat less salt and to consume enough iodine. That insults the public’s intelligence. Others fret about risks of iodine over-consumption. But this could be overcome with careful planning, and in any case is less dangerous than consuming too little iodine. For too long the world has relied too much on luck to keep people supplied with this life-enhancing mineral. That so many countries succeeded without mandatory iodisation programmes was an accidental public-health triumph. It would not take much for it to become an accidental disaster.
