Overview of Significant Scientific Information

Reference from the joint report of FAO/WHO expert consultation  on Human Vitamins and Minerals verbatim.

Shankar, A.H. & Prasad A.S. 1998. Zinc and immune function: the biological basis of

altered resistance to infection. Am. J. Clin. Nutr., 68(suppl.): 447S-463S

All biologic actions of iodide are attributed to the thyroid hormones. The major thyroid hormone secreted by the thyroid gland is T4 (tetra-iodo-thyronine). T4 in circulation is taken up by the cells and is de-iodinated by the enzyme 5' prime-mono-de-iodinase in the cytoplasm to convert it into tri-iodo-thyronine (T3), the active form of thyroid hormone. T3 traverses to the nucleus and binds to the nuclear receptor. All the biologic actions of T3 are mediated through the binding to the nuclear receptor, which controls the transcription of a particular gene to bring about the synthesis of a specific protein.

The physiologic actions of thyroid hormones can be categorised as 1) growth and development and 2) control of metabolic processes in the body. Thyroid hormones play a major role in the growth and development of brain and central nervous systems in humans from the 15th week of gestation to age 3 years. If iodine deficiency exists during this period and results in thyroid hormone deficiency, the consequence is derangement in the development of brain and central nervous system. These derangements are irreversible, the most serious form being that of cretinism. The effect of iodine deficiency at different stages of life is given in Table 34.

The other physiologic role of thyroid hormone is to control several metabolic processes in the body. These include carbohydrate, fat, protein, vitamin, and mineral metabolism. For example, thyroid hormone increases energy production, increases lipolysis, and regulates neoglucogenesis, and glycolysis.