Some 30% of the world's population, or two billion people, are deficient in iodine. Although the most severe cases occur in developing countries, Europeans are affected too, with about half of continental Europe being mildly iodine deficient.

Recently, reports from the UK, Belgium, and Germany have flagged declining or persistently inadequate iodine intakes in school-age children and/or their mothers.

Iodine is a critical nutrient particularly for the developing fetus and infant because of its vital role in brain development, and the WHO describes iodine deficiency as "the single most important preventable cause of brain damage".