IODINE

Iodine, also called iodide, is a naturally occurring mineral found in soil and ocean waters. About 70 -80% of the total iodine (15 -20 mg) found in the human body is present in the thyroid gland. 

Iodine derives its nutritional importance as a constituent of thyroid hormones. The thyroid hormones are indispensable for normal growth and development in humans. An adequate quantity of iodine is essential in the diet to ensure the proper functioning of the thyroid gland. 

Why is iodine essential to the human body?

Iodine is an essential part of the thyroid hormones – thyroxine (T4) and triiodothyronine (T3). These hormones play a key role in the growth and development of the body.

The thyroid gland is a major organ that regulates basal metabolism. Sufficient levels of iodine enhance thyroid functioning thereby, regulating metabolic activities. Having adequate levels of iodine protects the thyroid cells from free radical damage.

Supplementing iodine requirement balances T3 and T4 (thyroid hormones) levels.

Iodine is also protective against carcinogenic cells. In a process termed apoptosis, iodine helps to kill carcinogenic cells.

What are the symptoms and signs of iodine deficiency?

Iodine deficiency affects all populations at all stages of life, from the intrauterine stage to old age. However, pregnant and lactating women, women of reproductive age, and children younger than 3 years of age are considered the most important groups. Diagnosing and treating iodine deficiency occurring during fetal and neonatal growth leads to irreversible damage of the brain and central nervous system. This can consequently lead to irreversible mental retardation in children. Thus, iodine deficiency can cause a wide spectrum of disorders, like:

• Mild goiter – Large thyroid gland.
• Cretinism – Congenital, irreversible, and severe mental and growth retardation.
• Hypothyroidism – low BMR, apathy, slow reflex relaxation time with slow movements, cold intolerance, and dry skin and hair.
• Reduced fertility rate
• Increase in the chance of stillbirth

The symptoms of IDD differ depending on the life stage at which iodine deficiency occurs. Varying degrees of intellectual or growth retardation are apparent when iodine deficiency occurs in infancy or childhood and adolescence.

What is the daily requirement of iodine?

Small amounts of iodine are required daily since the human body cannot store the micronutrient for long.

The Recommended Dietary Allowance (RDA) for iodine as per the guidelines of the Indian Council of Medical Research (ICMR) is:

What are the food sources of iodine?

The iodine concentration in foods is highly variable and depends on the concentration of iodine content of the soil in that region. The iodine present in the upper crust of the earth is leached by glaciation, repeated flooding, and is carried to the sea. 

Seawater is, therefore, a rich source of iodine. The seaweed located near coral reefs has an inherent biological capacity to concentrate iodine from the sea.

Animal sources: Fish (marine water), shellfish, oysters, tuna, eggs, meat, and milk.

Plant sources: Nuts, cereal grains, broccoli, sea salt, seaweed, banana, green peas, and lima beans.

Can excess iodine cause toxicity?

Increased levels of iodine are to some extent tolerated by healthy individuals.

Excessively high levels could be toxic. Intake of high amount of iodine may precipitate hyperthyroidism, hypothyroidism, goiter, thyroid inflammation, and cancer of the thyroid gland.

The introduction of iodized salt as a public health measure to prevent goiter was first started in Switzerland and Michigan. Following this, the incidence of goiter and cretinism fell rapidly in these countries. 

The amount of iodide in drinking water is an indicator of the iodide content of the rocks and soils of a region, and it parallels the incidence of iodine deficiency among the inhabitants of that region. In general, iodine-deficient areas have water iodine levels < 2 mcg/L as in Nepal and Sub-Himalayan India compared with levels in cities like Delhi (9mcg/L) which is not iodine deficient.