Essential Vitamins & Minerals /

Iodine

01 In Brief

Iodine is a trace element that is required by the thyroid gland to produce thyroid hormones. It can be found in dairy products, salt water fish, eggs and some soy products. Thyroid hormones are essential for the normal development of the baby’s brain and nervous system. Low thyroid hormones during fetal and early postnatal life causes irreversible brain damage, with intellectual disability and neurological abnormalities. Luckily it is easily prevented.

The 2006 National Iodine Study, conducted by the Australian Centre of Iodine Deficiency Disorders (ACCIDD), identified an iodine deficiency among the Australian population. In March 2010 the Australian Government and the National Health and Medical Research Council (NHMRC) advised women planning to get pregnant, who are already pregnant, or who are breast feeding, to take 150 micrograms (mcg) of supplemental iodine daily in addition to their dietry intake.

02 What Do I Need To Know?

  • Iodine is a trace element needed by the thyroid gland to make thyroid hormones. It is essential for optimal neurological development of the fetus and of the infant in the first two years.
  • Breast-fed infants depend completely on their mother's iodine intake in order to produce their own thyroid hormones. This is why maintaining maternal dietary levels of iodine is so important during lactation. 

WHAT ARE THE CONSEQUENCES OF IODINE DEFICIENCY?

  • Congenital hypothyroidism due to iodine deficiency is the most common, preventable cause of intellectual disability in the world. Thyroid hormone is required for normal development (in particular neuronal migration and myelination) of the brain during fetal and early postnatal life. Low thyroid hormone during this critical period causes irreversible brain damage, with intellectual disability and neurological abnormalities. The most severe form is called cretinism (a syndrome characterised by permanent brain damage, mental retardation, deaf mutism, spasticity, and short stature). Moderate-to-severe iodine deficiency causes a range of neurological problems including decreased in IQ points by as much as 10-15 points, hearing impairment, and an increase in the incidence of ADHD
  • The potential adverse effects of mild-to-moderate iodine deficiency during pregnancy remain unclear. No controlled trials of iodine treatment in mild-to-moderately iodine deficient pregnant women have measured the long-term clinical outcomes such as maternal goitre (swelling of the thyroid gland) or infant development. However it is hypothesised that it is likely to cause subtle intellectual and behavioural problems. It is reassuring that these studies suggest that in areas of mild-to-moderate iodine deficiency, the maternal thyroid is able to adapt to meet the increased thyroid hormone requirements of pregnancy. (For further discussion see review by Zimmerman below.)
  • Severe iodine deficiency in the mother has also been associated with increased likelihood of miscarriages, stillbirth, preterm delivery, and congenital abnormalities in their babies.

IODINE REQUIREMENTS IN PREGNANCY AND LACTATION

  • Pregnant and breast feeding women require almost double the amount of iodine compared to non-pregnant women as the thyroid gland is very active in pregnancy. It is difficult to consume enough iodine daily to meet the increased needs during pregnancy and lactation. The NHMRC has recommended that all women who are considering becoming pregnant, who are pregnant or who are breast feeding should take a supplement of 150 micrograms daily of iodine in addition to the iodine in their diet. Pregnant and breast-feeding women should check the content of their pregnancy supplements to make sure they are taking the correct amount. 
  • The recommended supplement level of 150 micrograms has been determined by examining Australian data and by assessing the effect of mandatory iodine fortification of bread, and is considered safe and effective. There is no added benefit of taking more than the recommended amounts. Other iodine supplements, such as kelp or seaweed, are not recommended as they contain unreliable amounts of iodine and may also contain mercury. See reference to BonSoy below. 

IODINE DEFICIENCY IN AUSTRALIA

  • The National Iodine Study recognised that the Australian population is now mildly iodine deficient, especially in Tasmania, NSW and Victoria. In 2009 the World Health Organisation (WHO) also classified Australia as mildly iodine deficient.    
  • In October 2009 in Australia, the mandatory fortification of bread with iodised salt was introduced. The levels mandated were sufficiently low enough to prevent excess iodine consumption in children. Bread labelled as organic was excluded from mandatory fortification with iodine. 
  • Foods that contain iodine are fortified bread, shellfish, salt water fish, and dairy foods such as cow’s milk, cheese, yoghurt, ice cream etc. eggs, soy milk (see reference to soy milk in children from the RACP which contains a discussion of possible concerns), soy sauce and iodised salt. The amounts are variable and it is difficult for pregnant women to obtain the recommended daily intake from diet alone.  

BONSOY MILK: HIGH IODINE AND EFFECT ON NEWBORN

  • BonSoy soy milk was withdrawn from the Australian market in Australia in 2009 following detection of high levels of iodine. It was manufactured with a seaweed, kombu that contains extremely high levels of iodine.
  • Prior to its withdrawal several cases of hypothyroidism were diagnosed in babies whose mothers consumed BonSoy during pregnancy. These cases were detected on newborn screening tests performed on the third day after birth, which includes measurement of Thyroid Stimulating Hormone (TSH). TSH is produced by the pituitary gland in response to thyroid hormone levels, the lower the hormone level the higher the TSH. This occurs because ingestion of very large amounts of iodine can actually cause a reduction in the production of thyroid hormones (known as the Wolff-Chaikoff effect).

 

Women with pre-existing thyroid disease should seek advice from their doctor as recommendations about intake of iodine will vary, depending on their thyroid status.

03 What Others Say

  • NHMRC public statement on iodine supplementation for pregnant and breast feeding women - a well-written and well-referenced document.  

NHMRC public statement on iodine supplementation for pregnant and breast feeding women January 2010

04 I Want To Know More

I WANT TO KNOW MORE

  • National Iodine study from the Medical Journal of Australia: MJA 2006; 184 (4): 165-169 

Are our children iodine deficient?

  •  Literature review from the NHMRC  

NHMRC iodine during pregnancy and lactation

  • Extract from a newsletter from the Royal Australian and New Zealand College of Obstetricians and Gynaecologists and same article from the Australian Thyroid Foundation Pty Ltd  

RANZCOG and ATF Newsletter

  • Food Standards Australia and New Zealand

 Mandatory fortification of bread with iodine  

  • American Thyroid statement

Iodine supplementation for pregnancy and lactation - United States and Canada

  • WHO and UNICEF statement

Reaching optimal levels of iodine in pregnant and lactating women 

  • Article relating to the effects of mild iodine deficiency in pregnancy. 

PUB MED Delayed neurobehavioral development in children born to pregnant women with mild hypothyroxinemia during the first month of gestation: the importance of early iodine supplementation. Thyroid. 2009 May; 19(5):511-9. Berbel.P et al

  • Bonsoy and iodine MJA 2010; 193: 413-415

Iodine toxicity from ingestion of BonSoy 

  • Royal Australasian College of Physicians 

Paediatric and Child Health Division Policy on Soy-based milk in children

05 Clinicians Tools and Resources

  • Iodine Deficiency - a review: Michael B. Zimmerman

Zimmermann Endocrine Reviews 30 (4): 376-408

  • NHMRC Nutrient guidelines 2006

NHMRC Nutrient Values iodine

  •  RACGP website 24/12/2009

BonSoy information for Medical Practitioners

The information published here has been reviewed by Flourish Paediatrics and represents the available published literature at the time of review.
The information is not intended to take the place of medical advice.
Please seek advice from a qualified healthcare professional.
Read our terms and conditions

Last updated: 12/07/2011 by Dr Elizabeth Hallam*/Claire Galea