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Lack of iodine in Irish women’s diets may affect unborn children, research says

Irish women of child-bearing age have low levels of iodine in their diets and this could harm the neuropsychological development of their unborn children, according to the preliminary results of UCD research published in the Irish Journal of Medical Science. Low iodine levels can impact on the intelligence quotient (IQ) of unborn children and on the incidence of attention deficit and hyperactivity disorder (ADHD).

UCD researchers, Dr Peter Smyth, UCD School of Medicine & Medical Science, a principal researcher at UCD Conway Institute, and Professor Colm O’Herlihy from the National Maternity Hospital, Holles Street, have reported that iodine intake in the diet of women of child-bearing age seems to have declined since the mid-90’s – when they first investigated the issue.

Dr. Peter Smyth, UCD School of Medicine & Medical Science, principal researcher at UCD Conway Institute
Dr. Peter Smyth, UCD School of Medicine & Medical Science,
principal researcher at UCD Conway Institute

Dietary iodine deficiency represents the single greatest form of preventable brain damage and diminished IQ worldwide - the children of iodine deficient mothers are at risk of not reaching their full intellectual potential. Until the developing foetus possesses a functioning thyroid gland after 13 – 15 weeks gestation, it relies solely on the presence of maternal thyroid hormones to ensure neuropsychological development. The availability of these hormones is dependant on an adequate supply of iodine in the diet of the pregnant mother.

The research shows that dietary intake of iodine by Irish women is significantly less than the level recommended by the World Health Organisation. This is a greater problem in the summer months when available iodine in food sources such as dairy milk is at its lowest level.

Iodised salt is the primary dietary source of iodine and many countries have introduced systems of either voluntary or mandatory universal salt iodisation (USI). Changing the ingredients of salt to include iodine does not increase usage but improves the dietary quality of the consumer purchase.

However, Ireland and the UK are at the bottom of the USI league table with iodised salt making up only 3.3% of all salt sold. This compares poorly with many of our European neighbours, the United States, Asia and even African countries where between 60-90% of households use iodised salt. As a consequence, the availability of iodine in the Irish diet is entirely opportunistic and based on dietary preference for iodine containing foods such as seafoods (shellfish, white deep-water fish) and seaweed kelp.

‘While there is as yet no available evidence of widespread underactive thyroid function in the Irish obstetric population, the findings are a cause of concern’ says Dr Smyth. If the results are confirmed by a more comprehensive investigation, it may indicate a need to increase the dietary iodine supply to both pregnant women and those of childbearing age. The research is ongoing and is supported by the Health Research Board.

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