In 2007, the World Health Organization estimated that almost 2 billion people worldwide were not getting enough iodine in their diet. This iodine deficiency has damaging physical and economic consequences on these populations, especially pregnant women. For example, a 2008 review paper noted that “iodine-deficiency disorders are the most important cause of preventable mental retardation worldwide.” So, what is it that makes iodine so essential to the body?
Iodine is a building block of two hormones produced in our thyroid gland: thyroxine (T4) and triiodothyronine (T3). These thyroid hormones have widespread roles in our body, from protein synthesis in our cells to skeletal and neural development in babies.
Iodine is a chemical element that naturally occurs in saltwater and soil. According to the National Institute of Health, iodine is a building block of two hormones produced in our thyroid gland: thyroxine (T4) and triiodothyronine (T3). These thyroid hormones have widespread roles in our body, from protein synthesis in our cells to skeletal and neural development in babies.
To meet the body’s iodine need, the Center for Disease Control (CDC) recommends a daily dosage of 150 micrograms for adolescents and adults in the Second Nutrition Report. We can satisfy this daily intake through common sources of iodine including iodized salt, seafood, dairy products, and grains. For example, a one-fourth teaspoon serving of Morton Iodized Table Salt contains 45% of your daily recommended dosage of iodine.
After the body produces the thyroid hormones, the pituitary gland is responsible for measuring and responding to the amount of T4 hormone in our bloodstream. The American Thyroid Association uses the analogy of a thermostat and heater to describe how the pituitary gland and the thyroid gland work together. If the temperature in a room drops below a certain level, the thermostat will prompt the heater to turn on. Similarly, if there is too little T4 in the blood, the pituitary gland will signal to the thyroid gland to produce more T4. The pituitary gland sends this signal by releasing thyroid-stimulating hormone (TSH) into the bloodstream.
According to the CDC, the body becomes severely iodine deficient if iodine intake drops below 20 micrograms. Symptoms of chronic iodine deficiency include thyroid enlargement (goitre), where the thyroid gland enlarges and nodules develop as a result of high TSH levels in the blood. This process begins when the pituitary gland continues to release TSH to try to increase T4 levels in the blood. Since the body lacks the iodine to create more T4, there is no negative signal to stop releasing more TSH in the blood.
For pregnant women, the CDC’s recommended iodine dosage is higher because their bodies are both producing more thyroid hormones and supplying the iodine needed for fetal development. Thyroid hormones are crucial for normal brain development in fetuses. Severe iodine deficiency during pregnancy can lead to cretinism, a condition that impacts the child’s cognitive and motor abilities. The effects of iodine deficiency have long term impacts on the economic productivity of a country, with a 2006 review paper estimating a 10.3% loss in economic productivity to children of mothers with goitre.
As a result, combating iodine deficiency can have a large impact across a population. One cost-effective method to distribute iodine is through salt iodization, where table salt is augmented with small levels of iodine. One estimate lists the worldwide cost of iodine deficiency as$35.7 billion, while salt iodization would cost only $0.5 billion annually. The Iodine Global Network also lists iodized vegetable oil, potassium iodide tablets, and iodine fortified sugar and bread as other alternatives to supplying iodine. These methods are important in making sure that populations at risk of iodine deficiency have access to this nutrient, thereby reducing the global impact of iodine-deficiency disorders.