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Iodine. Metabolic control, modulation of oestrogen and foetal health

Iodine is commonly known to have a major effect on thyroid function, being a main component of the thyroid hormone thyroxine. However, Iodine has many other effects, from controlling the effects of oestrogen on breast tissue to protecting against the effects of radioactivity.

Iodine has been a favourite with those who want to lose weight for many years. As stated above, iodine is the main component of thyroxine, the thyroid component which controls metabolism. As metabolic rate controls the amount of "fuel" burned by the body for energy, iodine deficiency can result in a decreased metabolic rate, hence the supplementation by weight-watchers.

One of the other key functions of iodine is in the formation of the foetal nervous system. If the mother is deficient, there is a significant chance of the baby being born with cretinism (extremely low intellectual capacity). Iodine is also an important component of healthy connective tissues.

Research suggests that iodine is involved in moderating the effects of oestrogen on breast tissue. This seems to be particularly important in fibrocystic breast disease, where iodine has been shown to be of some use in overcoming the problem. given the role of oestrogen in breast cancer, their may be some part played by iodine here too.

The most widely known source of iodine is kelp, however it is also found in fish and, of course, iodised salt. Plant sources of iodine are totally dependant on where the plant is grown, due to the issue of depleted soils.

Functions of Iodine in the body

  • Required for manufacture of thyroxine (and therefore control of metabolic rate)
  • Essential to the normal development of the foetal nervous system
  • May protect against the effects of radioactivity
  • Can regulate the effects of oestrogen on breast tissue
  • A required component of healthy connective tissue

Iodine deficiency

Thanks to the introduction of iodised salt, iodine deficiency is now rare in the Uk and USA, although it does still occur in parts of Europe. Goitre, or enlargement of the thyroid gland, is the most common sign of deficiency. It is thought to affect over 200 million people worldwide and up to 6% of the population in areas with iodine deficient soils in the USA.

Deficiency itself may not be indicative of a lack of iodine in the diet, as many things can reduce iodine absorption or, more commonly, iodine utilisation in the thyroid. Such substances are called goitrogens and are listed under "factors affecting iodine levels".

Symptoms of Iodine deficiency

Goitre (swelling of the thyroid gland)
Chronic fatigue
Reduced immune system function
Dry skin
Excessive oestrogen production

Possible links to Parkinson's disease, multiple sclerosis and Alzheimer's disease.

Factors affecting iodine levels

Apart from iodine intake, a number of factors can affect iodine levels. minerals such as calcium, manganese, magnesium and fluoride are all goitrogens, which restrict iodine uptake by the thyroid. Goitrogens are also present in :

Bamboo shoots
Cassava root
Lima beans
Pine nuts
Sweet potato

However the goitrogens present in such foods can be largely inactivated by cooking. Tea then becomes the exception and drinking large amounts of tea will definitely affect iodine absorption and usage.

Normal amounts of Iodine in the diet

Age mcg/day
Children (0-1 year) 40 - 70
Children (1-10 years) 70 - 120
11yrs+ (inc adults) 150
Pregnancy 175
Lactation 200

Sources of dietary Iodine

Source mcg/100g
Iodised salt 7,000
Kelp, dried 5,350
Cooked haddock 200
Mackerel 133
Cod 100
Canned Pilchards 64
Plain yoghurt 60
Hard cheese 50
Cooked plaice 33
Salami 15
Canned corned beef 14
Roast Chicken 5

Iodine is also present in plants, however its presence is totally dependent on the availability of iodine in the soil, which is hugely variable from one area to another, due to the issue of depleted soils.

Iodine supplements

Two main forms of supplement are available, namely Iodine and iodides. Iodine compounds seem to be largely responsible for the effects of iodine on the role of oestrogen in breast tissue and are preferable. Iodides, on the other hand, seem to have more of an effect on thyroid function.

At large doses (greater than 750mcg) iodine supplements have been shown to reduce thyroid secretions, which should be considered by those who are trying to control their weight. At very high doses, iodine is toxic.

Back from Iodine to minerals

Related Links

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Plant extracts
Trace elements


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