Iodine deficiency was once common in mountainous areas of the United States and in the goiter belt around the Great Lakes; iodized salt, sold in the US since the 1920s, and a wider food supply have made overt deficiency uncommon in North America. Worldwide it remains the most common cause of preventable intellectual disability. Surveys suggest many pregnant women in the US may get too little iodine, and US iodine levels fell by more than half between the early 1970s and early 1990s before stabilizing.
Common symptoms
Enlarged thyroid (goiter), usually the earliest clinical sign
Hypothyroidism when intake falls very low (below about 10 to 20 mcg a day)
Impaired mental function and work productivity linked to hypothyroidism
In children, somewhat lower than average IQ
In severe deficiency during pregnancy: miscarriage, stillbirth, and cretinism in the child, which is irreversible
At-risk groups
Pregnant and breastfeeding women (RDA 220 and 290 mcg a day; the American Thyroid Association advises a 150 mcg potassium iodide supplement)
Women planning a pregnancy (also covered by the American Thyroid Association advice)
People who do not use iodized salt (sea salt, kosher salt and Himalayan salt are not usually iodized)
Vegans and people who eat little or no dairy, seafood or eggs
People in regions with iodine-poor soils who eat mostly local food
People with marginal iodine status who eat a lot of goitrogenic foods such as soy, cassava and cruciferous vegetables
When to see a doctorVisible swelling at the front of the neck, or symptoms you think may be thyroid related, are worth discussing with a doctor, who can order thyroid blood tests. Anyone planning a pregnancy or newly pregnant should check that their prenatal supplement contains iodine, because some do not. Too much iodine, including from high-dose supplements, can also disrupt thyroid function.