*1.2.2 Iodine's contribution to human body*

Iodine is a micronutrient which is present in the body in minute amount. The quantity of iodine required by an individual is about 150–200 μg/day [8]. Its main role is in the synthesis of thyroid hormone which is essential for the brain

#### **Figure 2.**

*Thyroid hormone synthesis in the thyroid gland (image reproduced with permission from the rights holder, Journal of Thyroid Research) [13].*

and physical development [9]. The regulation of thyroid hormones is under the control of the pituitary gland through thyroid-stimulating hormone (TSH). TSH secretion is regulated by a 'feedback' mechanism related to the level of thyroid hormones thyroxine [3,5,3′,5′-tetraiodothyronine (T4)] in the blood. Iodine is needed in the human body, and as the blood T4 falls, the pituitary TSH secretion is increased. In severe iodine deficiency disorders (IDD), the level of T4 remains lowered, and the level of TSH remains elevated. Both these measurements are used for diagnosis of hypothyroidism due to IDD at various stages in life particularly in neonates [10].
