The hidden danger of a salt-free diet

Last century, great progress was made when scientists came up with a non-invasive treatment that costs just a few pence. But the cure, adding iodine to table salt, falls foul of current medical advice to avoid salt. For this, and other reasons, iodine deficiency, which has never gone away in the developing world, is rearing its head again in countries such as Australia, the US and, some scientists fear, Britain.

While some experts are urging women of childbearing age to switch to iodised salt, others see this as controversial.

A correspondent to The Lancet pointed out recently: "The worldwide campaign to prevent iodine-deficiency disorders relies heavily on iodised salt. For example, a panel discussion on Australian television opened with these words: For years we've been told too much salt is bad for us, and that is true. But now there's a new public health campaign about how a certain kind of salt is essential, especially for children.' It seems unethical - and clearly self-defeating - to sell the public iodine by adding it to a substance we are now warning them to avoid."

But Dr Ron Fuge, senior research fellow in the Institute of Earth Science, at the University of Wales, argues that growing numbers of British women may be at risk of damaging their foetuses through a lack of this essential mineral. According to him, the dangers of small amounts of table salt are greatly exaggerated. "Every woman of child-bearing age in the UK should be looking for iodine supplements or at the very least, adding iodised table salt to home-cooked food."

In the UK, iodine deficiency was regarded until recently as a problem that had been "fixed". Now, however, doctors are coming across it again. The World Health Organisation says breast-feeding women in particular should be taking in three times the recommended daily allowance of the mineral. But according to Dr Fuge, many women are not.

"Borderline or mild iodine deficiency probably isn't a terribly serious problem for adults but it is for babies," he says, adding that although links with breast cancer had been suggested, looking at the Japanese high average intake and their low rate of breast cancer, "this has not really been proved. But it can cause poor brain development and that has been clearly shown".

He explains: "Plants don't take up iodine very well. The main natural sources are saltwater fish, shellfish and seaweed.

"One major solution to the problem of iodine deficiency last cen-tury was to iodise table salt. But the way we live has changed, people don't cook all their meals at home and the kind of salt that goes into processed food isn't iodized. Even when people do cook at home, many people don't use much salt because they know it is bad for them. If they do use salt it may be sea salt which doesn't have iodine. If you are in the supermarket there will be 20 kinds of salt and most won't have it - you have to look for it.

"Another major source in the UK is dairy, because iodine cleaning solution is used in milking and iodine is added to chicken feed. But there are a lot of people who don't drink much milk or eat many eggs because, again, they have been told it is bad for them."

In the United States, says Dr Fuge, the problem is being taken seriously. "When you got to a café there the little packets of salt they put on the tables say iodised salt'.

"The trouble here is that the authorities consider that this problem was put to bed in the 1970s and as far as they are concerned that is the end of the story."

Dr Mohammed Kibirige, a paediatric obstetrician in Middlesbrough, is trying to get funding to conduct a larger study after he found that up to 7% of pregnant women in the north of England were mildly to moderately iodine-deficient and that 40% of them were borderline deficient.

He noted that the figures appeared to be worse for Asian woman. "In the Asian sub-continent, iodine deficiency is dealt with through using iodised table salt," he explains. "Some Asian families do not eat much dairy food, which is the main source of iodine in the UK.

"It is crucial that we do more research. We need to find out how serious this problem really is."

He said iodine deficiency was a serious condition. "If you think of the body as a system, then an absence of iodine, which affects the production of hormones by the thyroid, can have all sorts of knock-on effects."

In Australia, iodine deficiency is once again regarded as a national problem, with the average Australian child having borderline iodine deficiency. In some areas, children are getting only half the recommended daily intake of iodine and there is evidence that their thyroids are larger than normal.

Although the reasons for the reduction of iodine intake are unclear, it may be because Australian dairy farms no longer use iodine solutions to wash cow's udders before milking. It may also be because of a reduction in the use of table salt.

Another possible cause may be that developed countries no longer use iodine in bread-making. It also appears that some fertilisers may interfere with animals' ability to absorb iodine. In the US, around 7% of pregnant women have been found to be moderately iodine deficient.

In the developing world, iodine deficiency is still a major problem. Worldwide, about two billion people - one-third of the globe - get too little iodine. Studies show that even moderate deficiency in pregnant women and infants lowers intelligence by 10 to 15 IQ points. The most visible and severe effects affect a minority, usually in mountain villages. But 16% of the world's people have at least mild goitre, a swollen thyroid gland in the neck.

"Find me a mother who wouldn't pawn her last blouse to get iodine if she understood how it would affected her foetus," said Jack Ling, chairman of the International Council for Control of Iodine Deficiency Disorders, a committee of about 350 scientists formed in 1985 to champion iodisation. The 1990 World Summit for Children called for the elimination of iodine deficiency by 2000. Working largely out of the public eye, the campaign made rapid progress: 25% of the world's households consumed iodised salt in 1990. Now, about 66% do.

But the effort has been faltering lately. When the target was not achieved by 2005, donor interest began to flag as avian flu and other threats got more attention.

Countries such as Kazakhstan, however, have continued to make huge strides in dealing with the problem. The impoverished Central Asian country is due to be signed off as free of iodine deficiency disorders next year. For a country which has struggled with the problem for decades, with large numbers of children exhibiting horrific symptoms, this is a major achievement.

The answer was simple and cheap. Down by the shores of the Aral Sea, the great inland sea which dried out under Stalin's immigration policies, a Unicef gifted iodiser is at work amid the salt mountains that remain there - 94% of Kazakhs are now using iodised salt.