Iodine – why is an adequate intake important?

May you have an iodine deficiency behind a lot of what is ailing you?

Iodine is found in seafood, iodised salt and some vegetables. It is important for essential hormone development in the human body. Inadequate intake of dietary iodine can lead to an enlarged thyroid gland (goitre) or other iodine deficiency disorders. Iodine deficiency is the world’s leading cause of mental retardation in children.

Iodine is found in foods as iodide. Our bodies need it to make thyroid hormones. The thyroid is a gland in the throat that regulates many metabolic processes, such as growth and energy expenditure. The two main thyroid hormones, thyroxine and tri-iodothyronine, are synthesised from the amino acid, tyrosine, and from iodide.

The thyroid hormones regulate the body’s metabolic rate and promote growth and development throughout the body, including the brain. If there isn’t enough thyroid hormone circulating in the blood, the brain sends a chemical message to the thyroid gland, which then releases a measured dose of these hormones. If a person’s diet is too low in iodine, the brain keeps sending chemical messages to the thyroid in vain. In an attempt to make more thyroid hormone, the gland gets larger and larger. This overgrowth of the thyroid gland is called a goitre.

Long term deficiency can be serious

An enlarged thyroid gland, or goitre, isn’t the only side effect of inadequate iodine in the diet. Other symptoms include dry skin, hair loss, fatigue and slowed reflexes.

In the developing fetus, baby and young child, the effects of iodine deficiency are serious, including stunted growth, diminished intelligence and retardation. Lack of iodine is a major problem in developing countries and is considered to be the world’s number one cause of preventable intellectual disability in children. Vegetarians may also be at risk of iodine deficiency if they do not eat seafood. Instead they can get their iodine from iodised table salt or seaweed. A study published in Sep-Oct 2003 Annals of Nutrition and Metabolism showed that 25% of the vegetarians, 80% of the vegans and 9% of those eating a mixed diet had low iodine status.

Sources of iodine

Iodine is found in seawater, so any type of seafood is a rich source of this element, particularly seaweed (e.g kelp). Despite coming from the ocean, sea salt is not a good source of iodine. Iodised salt is perhaps the most common source of iodine in the Western diet and can provide enough iodine to avoid low thyroid activity. Since an adult only requires around one teaspoonful of iodine over a lifetime, eating fish once a week is enough to fulfill the average iodine requirement.

Some vegetables also contain iodine, but only if they are grown in iodine-rich soils. Certain regions of Australia, such as Tasmania and the Australian Capital Territory, have low levels of iodine in the soil.

Iodine can be neutralised by certain foods

The value of dietary iodine can be reduced by vegetables from the brassica family, which includes cabbage, brussels sprouts, raw turnip, broccoli, and cauliflower. In circumstances where both large quantities of these foods are eaten and the levels of dietary iodine are marginal, goiter could develop.

Iodine intake in Australia has dropped

Low dietary levels of iodine were thought to be a problem in the past or in developing countries only. However, some researchers suspect that iodine intake levels in Australia have dropped considerably, perhaps by as much as half, over the past few decades. To find out how big the problem is and what might be done about it, a nation wide study is set to start in Australia. Some reasons for low iodine intake may include:

  • A reduction in the use of salt in cooking and table salt (particularly iodised salt).
  • Consuming most of our salt in processed foods, which do not contain iodine.
  • Less iodine in milk because of changes in treatment methods.
  • Iodine levels in Australian soils may have dropped

 

How much iodine do we need

The recommended daily dietary intake of iodine in Australia:

  • 150 micrograms for men
  • 120 micrograms for women (150 micrograms during pregnancy, 170 micrograms during lactation)
  • Children 70-150 micrograms
  • Infants 50-60 micrograms

Excessive amounts of iodine can also lead to goitre. This has occurred where foods such as seaweeds, which are rich in iodine, are commonly eaten. However, it is unlikely that any harmful effects would occur with habitual intakes up to 300 micrograms per day.

  • One teaspoon of iodised salt provides 150 micrograms of iodine
  • 1 serve (100g) of seafood provides about 60 micrograms
  • 100g of vegetables or meat or eggs provides about 25 micrograms of iodine
  • 100g of dairy products or bread/cereals provides about 10 micrograms.

Anyone on a low-salt diet should consider eating a serve of seafood every week to make sure their iodine levels are adequate, particularly pregnant women, as lack of iodine can retard normal development in their baby. Vegetarians should get iodine from iodised salt or seaweed.

Things to remember:

  • Dietary iodine is needed to make essential thyroid hormones.
  • Inadequate iodine can cause mental retardation and stunted growth in children and an enlarged thyroid gland (goitre) in adults.
  • Good sources of iodine include iodised salt and any type of seafood, including seaweed.

Japanese people eat very large amounts of seaweed. Thyroid issues seem much lower in those who do.

References

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