Amid the recent furore over the availability of iodine tablets in the event of a nuclear accident at Sellafield or beyond, one fact was largely overlooked. In common with most of western Europe, the Republic is an area of mild or borderline iodine deficiency and, as a result, the population is at greater risk of suffering negative health effects both in and outside of nuclear emergencies.
This not only makes us more vulnerable to absorbing any radioactive iodine that might be emitted from a nuclear installation following an accident, but also makes us more susceptible to iodine-deficiency disorders that, in children, can result in diminished IQ and learning capacity. Our studies of dietary-iodine intake in the Irish population, particularly in pregnant mothers and their babies - carried out at the thyroid diagnostic unit of University College, Dublin - have shown that by World Health Organisation criteria, the Irish diet can be classified as iodine insufficient.
Uptake of radioactive iodine by the thyroid gland can result in the development of thyroid cancer. This was particularly evident in the Chernobyl nuclear disaster, following which a dramatic increase in childhood cancer was observed.
A feature of the Chernobyl accident was the relative dietary-iodine deficiency of the population living around the reactor in Belarus and Ukraine, resulting in iodine-deficient thyroid glands taking up greater amounts of radioactive iodine.
Iodine in the diet is selectively trapped by the thyroid, a two- lobed gland located in the neck, on either side of the windpipe. This trapping ability allows the thyroid to concentrate iodide to about 50 times its level in the bloodstream. Trapped iodide provides raw material for the production of thyroid hormones, controlling many processes in the body.
The thyroid does not discriminate between stable - non-radioactive - and radioactive iodine. The amount of iodine taken up by the thyroid is governed by the amount already there. A thyroid relatively empty of iodine will take up more iodine than one already replete with it.
So the simple expedient of taking iodine tablets, and thereby saturating the thyroid with iodine, would offer protection against the results of ingestion of radioactive iodine following a nuclear accident. A single tablet of iodine, containing potassium iodide in the range of 50-100 milligrams (children would receive half the dose administered to adults), will provide adequate thyroid blockade for 24 hours.
Iodine tablets must be taken very early following an accident - within six hours, for greatest effectiveness - if thyroidal uptake of radioactive iodine is to be prevented. This might not be feasible if tablets have to be distributed following the accident, thus making the case for predistribution to designated sites or, preferably, to individual homes.
It must be emphasised that stable iodine protects only against the uptake of ingested radioactive iodine. It does not provide protection against other radioactive substances or against external irradiation caused by radioactive iodine.
The question of deciding what steps should be taken to protect against the consequences of a nuclear accident are not unique to the Republic. The consequences of the Chernobyl accident have caused an increasing recognition of the radiosensitivity of the developing thyroid, however, leading to a progressive downward revision of the level of radiation that may constitute a risk for developing thyroid cancer.
With luck, the Republic will not encounter a nuclear accident of the magnitude of Chernobyl, but a population at risk could be given significant protection against the effects of radioactive-iodine uptake simply by increasing their dietary-iodine intake.
The most effective method of achieving iodine sufficiency, recommended by the World Health Organisation, is iodisation of table salt. Consumption of table salt would not have to change; only minor alterations to the production of salt would be needed.
Unlike in some other countries, iodisation of table salt is not mandatory in the Republic, and recent figures suggest that only 2 per cent of salt sold here is iodised. According to the World Health Organisation, only 27 per cent of European households have access to iodised table salt, compared with 90 per cent in the Americas, 70 per cent in South-East Asia and 63 per cent in Africa.
While there is no absolute protection against the harmful effects of ingested radioactivity, taking stable iodine either immediately, in the form of iodine tablets, or long term, by increasing dietary-iodine intake, can at least provide a degree of protection to susceptible individuals in exposed populations.
Peter P.A. Smyth is a senior lecturer in medicine and director of the endocrine laboratory at University College, Dublin, and a member of the Government's consultative committee on nuclear-emergency planning