Deficiency: 

Why does iodine deficiency occur?

Iodine deficiency occurs when the soil is poor in iodine, causing a low concentration in food  products and insufficient iodine intake in the population. When iodine requirements are not met, the thyroid may no longer be able to synthesize sufficient amounts of thyroid hormone.

Effects of iodine deficiency: 

Iodine deficiency has multiple adverse effects on growth and development. Iodine deficiency disorders result from inadequate thyroid hormone production secondary to  insufficient iodine. During pregnancy and early infancy, iodine deficiency can cause irreversible  effects.

Under normal conditions, the body tightly controls thyroid hormone concentrations via TSH.  Typically, TSH secretion increases when iodine intake falls below about 100 mcg/day. TSH  increases thyroidal iodine uptake from the blood and the production of thyroid hormone.  However, very low iodine intakes can reduce thyroid hormone production even in the  presence of elevated TSH levels. 

If a person’s iodine intake falls below approximately 10–20 mcg/day, hypothyroidism occurs, a condition that is frequently accompanied by goiter. Goiter is usually the earliest clinical sign of iodine deficiency. In pregnant women, iodine deficiency of this magnitude can cause major neurodevelopmental deficits and growth retardation in the fetus, as well as miscarriage and still birth. Chronic, severe iodine deficiency in utero causes cretinism, a condition characterized by intellectual disability, deaf mutism, motor spasticity, stunted growth, delayed sexual maturation, and other physical and neurological abnormalities .  

In infants and children, less severe iodine deficiency can also cause neurodevelopmental deficits  such as somewhat lower-than-average intelligence as measured by IQ Mild to moderate  maternal iodine deficiency has also been associated with an increased risk of attention deficit  hyperactivity disorder in children. In adults, mild-to-moderate iodine deficiency can cause  goiter as well as impaired mental function and work productivity secondary to  hypothyroidism. Chronic iodine deficiency may be associated with an increased risk of the  follicular form of thyroid cancer. 

Prevention: 

At a population level, iodine deficiency disorder (IDD) can be prevented by the iodization of  food products or the water supply. In practice, this is usually achieved by iodization of salt. An alternative in some developing countries has been the periodic injection of iodized oil supplements.