Iodine Deficiency
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.
