Iodine occurs in seawater. A small amount of iodine from seawater enters the atmosphere and, through rain, enters ground water and soil near the sea.
In many areas, including the United States, table salt is fortified with iodine (in its combination form iodide) to help make sure people consume enough.
Iodine deficiency is rare in areas where iodine is added to table salt. However, the deficiency is common worldwide. People living far from the sea and at higher altitudes are at particular risk of iodine deficiency because their environment, unlike that near the sea, contains little, if any, iodine.
When iodine is deficient, the thyroid gland enlarges, forming a goiter, as it attempts to capture more iodine for the production of thyroid hormones. The thyroid gland becomes underactive and produces too little thyroid hormones (hypothyroidism). Fertility is reduced. In adults, hypothyroidism may cause puffy skin, a hoarse voice, impaired mental function, dry and scaly skin, sparse and coarse hair, intolerance to cold, and weight gain.
If pregnant women have iodine deficiency, the risk of miscarriage and stillbirth is increased. The fetus may grow slowly, and the brain may develop abnormally. Unless affected babies are treated soon after birth, a disorder that causes intellectual disability and short stature (cretinism) develops. Babies with cretinism may be deaf and mute. They may have birth defects and/or hypothyroidism.
Iodine deficiency is diagnosed based on blood tests indicating low levels of thyroid hormones or a high level of thyroid-stimulating hormone (TSH) or based on the presence of a goiter (only in adults).
Doctors do a blood test to check for hypothyroidism, including that due to iodine deficiency, in all newborns.
Imaging tests, such as ultrasonography or thyroid scanning, may be done to measure the thyroid gland and to evaluate any abnormalities.
Pregnant women often consume inadequate amounts of iodine. Thus, pregnant and breastfeeding women should take prenatal vitamins containing 250 micrograms of iodine daily.
Infants, children, and adults with iodine deficiency are treated with iodine supplements taken by mouth. Infants are also given supplements of thyroid hormone taken by mouth, for several weeks and sometimes throughout life. Children and adults may also be given thyroid hormone supplements.