Mild to severe iodine deficiency exists in 30 countries; an estimated 1.9 billion people have insufficient iodine intake. Moderate iodine deficiency during gestation and infancy can cause manifestations of hypothyroidism, deafness, short stature, and lowers a child’s intelligence quotient by 10–15 points. Even mild-to-moderate iodine deficiency appears to impair a child’s perceptual reasoning and global cognitive index. Severe iodine deficiency increases the risk of miscarriage and stillbirth. Cretinism occurs in about 0.5% of live births in iodine-deficient areas.
Although iodine deficiency is the most common cause of endemic goiter, there are other natural goitrogens, including certain foods (eg, sorghum, millet, maize, cassava), mineral deficiencies (selenium, iron, zinc), and water pollutants, which can themselves cause goiter or aggravate a goiter proclivity caused by iodine deficiency. In iodine-deficient patients, smoking can induce goiter growth. Pregnancy aggravates iodine deficiency. Some individuals are particularly susceptible to goiter owing to congenital partial defects in thyroid enzyme activity.