Thyroid gland is part of the endocrine system and secretes a hormone which helps the body to carry out some very important functions. It uses iodine to make this hormone. Iodine was discovered by Bernard Courtois 1811 in an attempt to more efficiently produce gun powder for Napoleon’s army. It’s name is from the Greek ‘Iodes’ for violet – the colour of it’s vapour when burnt. Iodine is by far the heaviest of the required human elements in terms of atomic weight. Iodine is essential for normal development and metabolism in all animals including humans. Deficiencies can cause spontaneous abortion, increased infant mortality, hypothyroidism, cretinism, goitre and mental defects. It is interesting that goitre as a medical problem has been discussed in medical text since 2700 BC. Chinese physicians documented

A very simple way to diagnose hypothyroidism is to take your temperature in the armpit for about 6-7 minutes as soon as you wake up in the morning while still in bed, do
it for 3 consecutive days. If the temperature is 97 or below each day you have hypothyroidism.

that goitre could be reversed by ingesting burnt seaweed powder and eventually by ingesting animal thyroid tissue. Both treatments came to be generally accepted. Severe lack of iodine produces the morphological and cognitive impairments known as cretinism. Thyroid gland is chemically unique due to its dependence
on iodine. In a severe deficiency of adequate iodine the gland cannot produce adequate amount of hormone. This leads to hypothyroidism. If this occurs early in life, the brain never develops. Collectively all adverse effects emerging from lack of iodine are currently called Iodine Deficiency Disorders (IDD). The World Health Organisation (WHO) estimates that roughly 2 billion humans (30% of world population) suffer from or are at risk for IDD. Biochemically iodine’s main function is as

an essential component of thyroid hormones.
Thyroxine (T4) and triodothyronine (T3) are comprised of approximately 65 and 59% iodine by weight respectively. All mammals depend on thyroid hormones for regulation of enzymatic activity and protein synthesis. In a slightly deficient state the thyroid swells up to compensate often leading to goiter. Iodine is readily absorbed via the entire length of intestinal tract. Although iodine deficiency is the most common cause for hypothyroidism globally, nearly all cases of hypothyroidism in the industrialised world are secondary to autoimmune disease.

Thyroid hormones perform the following functions:

1. Regulation of basal metabolic rate
2. Regulation of macronutrient metabolism.
3. Regulation of development, growth and sexual maturation.
4. Regulation of breathing
5. Regulation of heart rate
6. Regulation of body weight
7. Regulation of body temperature
8. Regulation of muscle strength and many more

If the T3 and T4 are either too high or two low they produce symptoms of hyperthyroidism and hypothyroidism respectively. Hypothyroidism is a common problem and causes tiredness, weight gain or difficulty in losing weight, lower than normal body temperature. Hyperthyroidism causes anxiety, anorexia, weight loss, hand tremors, increase in heart rate.

Dietary iodine

Iodine is abundant in soil and sea water, but regional levels vary tremendously based on past snow, rain and glaciation all of which leach it to the ocean. Many regions in the world in the past have been known as goitre belt due to low soil iodine. The regional variation in goitre is
due to the fact that the amount of iodine found in the plants varies with the concentration of the iodine in the soil. Since iodine is abundant in sea water, nearly all foods from the sea are rich in it. Iodine fortification of salt has all but eliminated goitres but hypothyroidism is prevalent widely. Goitrogens are plant chemicals that block the iodine uptake and are found in cruciferous vegetables, millet and soy. These chemicals are heat-labile and rendered

inactive when cooked. If these foods are eaten raw on a regular basis hypothyroidism may develop. Dietary source of iodine Along with the plant food, the other large sources of iodine in our diet include ocean-derived sea food, dairy products and bread. Dairy products can vary a lot in iodine concentration depending on the supplemental iodine given to the cattle. The densest source of iodine in foods is seaweeds which is eaten in many coastal areas of the world. Iodised salt is the main dietary source of iodine in most countries, but salt used in food processing and restaurants is generally not iodised to prevent toxicity. People who eat a lot in restaurants and also take pre made groceries must be careful as the prime intake of salt should come from home cooked food using iodised salt. Also consuming a variety of fruits, vegetables, meats, sea food, and grains can provide a basal amount of iodine. Pregnant and lactating women should be advised to take multivitamin supplement containing iodine.

SAFE UPPER LIMIT

The institute of Medicine has established the following Tolerable Upper Intake Levels (ULs) for iodine:

• 1-3 years: 900 ug;
• 4-8 years: 300 ug;
• 9-13 years: 600 ug;
• 14-18 years: 900 ug;
• 19 years and older: 1100 ug;
• Pregnant women 14-18 years: 900 ug;
• Pregnant women 19 years and older: 1100 ug;
• Lactating women 14-18 years: 900 ug;
• Lactating women 19 years and older: 1100 ug;