Concerns are being raised over the intellectual development of babies in the womb after research revealed Irish women of child-bearing age are not getting enough iodine in their diet.
Research carried out at the Conway Institute at University College Dublin (UCD) has found a decline in the amount of iodine detected in Irish women over the past decade.
A lack of iodine could harm the neuropsychological development of an unborn foetus, impact on their intelligence and on the incidence of attention deficit and hyperactivity disorder (ADHD).
Dr Peter Smyth, a senior lecturer at UCD, said: "What we are concerned about is the actual intellectual development of the child. We don't know whether this is at risk, but there is a potential that it could be, so we feel we should study iodine intake in the Irish population and see if the trend we have detected . . . and then study the significance."
The preliminary results of the study, supported by the Health Research Board and carried out by Dr Smyth and Professor Colm O'Herlihy from the National Maternity Hospital, Holles Street, found iodine intake in the diet of women of child-bearing age has declined since a similar study undertaken in the mid-1990s.
Dr Smyth said there was as yet no available evidence of widespread underactive thyroid function in the Irish obstetric population but that the findings were a cause of concern. He said if the findings were 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 researchers said dietary iodine deficiency represents the single greatest form of preventable brain damage and diminished IQ worldwide. The dietary intake of iodine by Irish women was found to be significantly less than the level recommended by the World Health Organisation.
The researchers said iodine was very important in the diet as it formed the basic building material for thyroid hormones, which aids the development of the brain.
"A baby in the womb, a foetus, has no thyroid gland of its own until about 13 to 15 weeks, so it is totally dependent upon thyroid hormones provided by the mother, so if the mother doesn't have enough iodine she doesn't produce enough thyroid hormones and therefore the baby in this crucial developmental period does not have access to thyroid hormones," Dr Smyth said.
The research looked at 54 women attending the National Maternity Hospital in the first trimester of their pregnancy, and measured the iodine content of dairy milk on sale in Dublin.
Many countries have introduced iodised salt which is proving a main dietary source of iodine. But in Ireland, iodised salt makes up only 3.3 per cent of all salt sold. Iodine can be sourced from marine products such as fish or seaweed, as well as dairy products.