In the body, iodine (I) is involved primarily in the synthesis of 2 thyroid hormones, thyroxine (T4) and triiodothyronine (T3).
Iodine occurs in the environment and in the diet primarily as iodide (1). In adults, approximately 80% of the iodide absorbed is trapped by the thyroid gland. Most environmental iodine occurs in seawater; a small amount enters the atmosphere and, through rain, enters ground water and soil near the sea. Thus, people living far from the sea and at higher altitudes are at particular risk of iodine deficiency.
Fortifying table salt with iodide (typically 70 mcg/g) helps ensure adequate intake (150 mcg/day). Requirements are higher for pregnant (220 mcg/day) and lactating (290 mcg/day) women.
Iodine deficiency s rare in areas where iodized salt is used but common worldwide. Iodine deficiency develops when iodide intake is < 20 mcg/day.
Treatment reference
1. Zimmermann MB, Boelaert K. Iodine deficiency and thyroid disorders. Lancet Diabetes Endocrinol. 2015 Apr;3(4):286-95. doi: 10.1016/S2213-8587(14)70225-6
Symptoms and Signs of Iodine Deficiency
In mild or moderate iodine deficiency, the thyroid gland, influenced by thyroid-stimulating hormone (TSH), hypertrophies to concentrate iodide in itself, resulting in colloid goiter. Usually, patients remain euthyroid; however, severe iodine deficiency in adults may cause hypothyroidism (endemic myxedema). It can decrease fertility and increase risk of stillbirth, spontaneous abortion, and prenatal and infant mortality.
Severe maternal iodine deficiency retards fetal growth and brain development and sometimes results in birth defects. Manifestations of congenital hypothyroidism may include intellectual disability, deaf-mutism, difficulty walking, short stature, and sometimes hypothyroidism (cretinism).
Diagnosis of Iodine Deficiency
Assessment of thyroid structure and function
Diagnosis of iodine deficiency in adults and children is usually based on thyroid function tests (primarily TSH), examination for goiter, and imaging tests identifying abnormalities in thyroid function and structure. All neonates should be screened for hypothyroidism by measuring the TSH level.
Treatment of Iodine Deficiency
Iodide with or without levothyroxineIodide with or without levothyroxine
Infants with iodine deficiency are treated with levothyroxine 3 mcg/kg orally once a day for one week plus iodide 50 to 90 mcg orally once a day for several weeks to quickly restore a euthyroid state.Infants with iodine deficiency are treated with levothyroxine 3 mcg/kg orally once a day for one week plus iodide 50 to 90 mcg orally once a day for several weeks to quickly restore a euthyroid state.
Children are treated with iodide 90 to 120 mcg once a day and levothyroxine until they are able to synthesize T4.Children are treated with iodide 90 to 120 mcg once a day and levothyroxine until they are able to synthesize T4.
Adults are given iodide 150 mcg once a day. Hypothyroidism due to iodine deficiency can be treated by giving levothyroxine.Adults are given iodide 150 mcg once a day. Hypothyroidism due to iodine deficiency can be treated by giving levothyroxine.
Women who are pregnant or breastfeeding should consume adequate iodine. In areas where iodized salt is not regularly ingested, such women should take 225 to 375 mcg of iodine daily. In the United States and Canada, supplementation with 150 mcg is recommended, and this amount is included in most but not all prenatal vitamins.
Serum TSH levels are monitored in all patients until the levels are normal (ie, < 5 mcIU/mL).
