The measurement of urinary iodine provides an accurate approximation of dietary iodine intake. 

The majority of iodine that is ingested (90%) is excreted via the urine. When there is adequate amounts of iodine in the body to support various bodily systems, the body offsets excess by excreting it in the urine. Urinary iodine measurements provide a biological indicator of Iodine deficiency disorders by determining whether the body has sufficient levels.

Iodine's main action is involved in thyroid function. Due to the numerous actions carried out by the thyroid, the implications of iodine deficiency are significant.

The major hormone secreted by the thyroid is thyroxine, also called T4 because it contains 4 iodine atoms. To exert its effects, T4 is converted to T3 by the removal of one iodine atom. This occurs mainly in the liver and other tissues where T3 acts, such as the brain.  Other actions include the formation and integrity of normal breast tissue, foetal brain development and function, and anti-microbial effects.

Iodine Deficiency is the commonest worldwide cause of thyroid disorders. A low iodine diet can cause hypothyroidism, an enlarged thyroid gland (goitre) and can affect fertility, pregnancy and neuro-developmental disorders in newborns.