Iodized Salt and Public Health: How Iodine Fortification Prevented Goiter and Where Gaps Remain

Why iodine, and why salt

Iodine is needed to make thyroid hormones, and the body cannot make it, so it has to come from food. [1] Few foods are rich in iodine, and the amount in plant foods depends on the soil they grow in. [1][3] The WHO's first estimate of global goiter (a swollen thyroid), in 1960, suggested 20% to 60% of the world's population was affected. [2]

Lack of iodine during pregnancy can severely impair a fetus's brain and physical development and cause irreversible cognitive deficits in children. [1]

Salt was chosen because almost everyone eats it and the technology for adding iodine is simple and cheap. [1] The WHO and UNICEF recommended iodizing food-grade salt in 1994. [1]

How the programs are set up

• The compound and amount. The WHO's 2014 guideline names potassium iodate or potassium iodide as the compounds to use, and suggests different iodine amounts for different national salt intakes. [1] Salt is called adequately iodized at 15 to 40 parts per million iodine. [2]
• Amounts have come down. Assuming a 10 g daily salt intake, the suggested iodine added was 22 to 45 mg per kg of salt in 1994, 20 to 40 in 1996 and 18 to 22 in 2014. [1]
• Monitoring. A population's median urinary iodine concentration is a reliable indicator of its recent iodine intake, and 100 to 299 mcg per liter indicates adequate intake. [1] Countries are meant to adjust salt iodine amounts if monitoring shows intake is too low or too high. [1]
• Law. Between 1942 and 2020, 123 countries introduced mandatory salt iodization legislation. [2]

What the research and reports found

Where the gaps are

• Programs can fail. Madagascar's mandatory program fell apart through political instability, and in Vietnam weaker legislation allowed non-iodized salt in. [2]
• Strong health systems are no guarantee. Iodine intake was reported inadequate in Norway, Germany and Finland, which have strong health systems. [2]
• Processed food. Many national programs have focused mainly on household salt, though in many middle- and high-income countries most salt is eaten in processed foods. [2]
• Pregnancy. Many pregnant women in low- and high-income countries, including the United States and several European countries, have low iodine intakes, but the thresholds that define deficiency in pregnant and non-pregnant women remain uncertain. [2] For adult intake figures, see Mineral Intake References Compared; for pregnancy, see Iodine in Pregnancy, Breastfeeding and Infant Development.
• Over-iodization. A 2022 analysis of 110 countries found 87% specified more iodine in their national salt standard than the 2014 WHO guideline suggests, yet it found no indication of excess intake linked to this. It cautioned that poor compliance may hide the effect, and that universal, well-enforced iodization at those amounts could lead to excess. [1]
• Food sources of excess. In South Korea, a high median urinary iodine was attributed mainly to iodine-rich seaweed. [2] See Seaweed, Sea Moss and Kelp.

Salt reduction and iodine: do they conflict?

Many countries are also urging people to eat less salt. A 2024 review notes concern that iodine deficiency could re-emerge when salt falls, and lays out how both salt reduction and iodine fortification can be integrated. [4] Sodium advice is on Sodium Intake Guidelines by Country. This is a policy question, so it is not a reason to change your own salt use without asking a clinician if you have blood pressure, kidney or thyroid conditions.